We discuss the application of high-resolution x-ray diffractometry to studies of semiconductor heterostructures. A new technique has been devised which extends structural measurements into the time domain. Using x-ray synchrotron radiation in conjunction with dispersive optics and fast x-ray area detectors we have been able to study for the first time the structure of heterointerfaces undergoing thermal processing. The techniques are illustrated with results on the strain kinetics of SQW''s and ion-implanted InAli_As layers.

Recent experimental and theoretical results on cation incorporation dynamics in the MBE growth of 111-V materials will be presented. The measurement techniques were reflection high energy electron diffraction and modulated beam relaxation spectroscopy supported theoretically by Monte Carlo simulation. The concept of surface accumulation of cations (especially indium) during conventional MBE growth is introduced and adatom migration and attachment kinetics are considered in detail.

Two quaternary Ill-V systems are available for InP based opto and micro-electronics : InGaAsP and InGaAlAs. The first has been extensively studied with remarkable success for opto-devices as well as OEIC''s. Although the second has proved ofinterest for high performance microelectronic devices it was not considered until recently as a challenger for optoelectronics. After a review of the different techniques used for producing structures in the two systems we show that the InGaAlAs system tends to drive new interest also in the opto-electronic field. It is well suited to MBE especially when compositional variations are required. Good material has been prepared and characterized leading to 1 . 5 micron emitting quantum well laser diodes and modulators that compare to those obtained from the InGaAsP systems I - SOMEDATA ON INGAASP VERSUS INGAALAS Two quaternary alloys can be epitaxially grown on InP provided that the following relations are fulfilled: InGa1AP1 : 1 - x (1 - 0. 53) y and InGaAlAs (In053Ga047As)1 (In0 52Al048As). The materials range from In0 53Ga047As to InP in the first case and from In0 53Ga0 47As to In0 52A10 48As in the latter case thus covering the bandgap (300 K) : 0. 75 to 1. 45 eV and 0. 75 to 1. 34 eV respectively. 34 / SPIE Vol. 1361 Physical Concepts of Materials for Novel Optoelectronic Device Applications 1(1990)

This paper will examine the effect of quantum well confinement on a variety of radiative processes such as impurity binding energies excitonic recombination (both free excitons and bound excitons) and other phenomena observed in bulk material and now being investigated in low dimensional quantum structures. Emphasis will be on one-dimensional confinement provided by quantum wells. Extension to lower dimensional structures will be discussed.

Photoreflectance a contactless form of electromodulation is a very useful technique for the in-situ monitoring of important growth/processing parameters. This paper will discuss some recent applications including (a) determination of substrate temperature (GaAs InP) and alloy composition (GaAlAs InGaAs) during actual growth condition at elevated temperatures (b) evaluation of interfacial quality of a strained layer In0 2Ga0 8As/GaAs single quantum well and (c) studies of Fermi level pinning. The latter includes measurements in an MBE machine before (and after) exposure to air and the effects of metallization (Schottky barrier formation) in a UHV chamber.

InP-based (AlInAs/GaInAs) high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) have demonstrated a substantial performance improvement over GaAs-based devices. HEMTS with extrinsic over 200 GHz fmax''s over 300 GHz and extremely low noise figures with high associated gain ( 5 dB with 15 dB at 12 GHz and 5 dB with 8 dB at 60 GHz) have been achieved. HBTs have exhibited fT''s exceeding 90 GHz with fmax''s of 70 GHz. Digital and analog ICs have shown state-of-the-art performance a 25 0Hz divide by 4 a 9 GHz 8/9 dual modulus divider and a dc coupled feedback amplifier with 33 GHz bandwidth. The status of these device technologies for high performance microwave and millimeter-wave applications will be discussed.

The room teffiperature stiniulated emission near ultraviolet from ntype GaN film which was grown by MOVPE on a sapphire substrate is observed for the first time. The low energy electron beam irradiation treatment lowers the resistivity of Mgdoped GaN which tends to show p-type conduction and simultaneously enhances blue luminescence efficiency drastically. The pn junction LED shows strong both nearbandedge UV ends sion from nlayer and blue emission from player.

A pnpn photothyristor structure made of ITT-V semiconductors may function as an optoelectronic neuron. The input and output can be electrical and/or optical. The device responds to light and can emit light. The device is endowed with thresholding and memory capabilities. A group of such devices can be integrated in an array to form a neural net capable of inter-neuron interactions that include global and local inhibition and enhancement of response. These integrated neurons may eventually lead :. o learning and other useful applications.

We first show how the characteristical properties of defects (energy level capture cross-sections) in systems such as single heterostructures and superlattices can be deduced from the corresponding properties in a bulk material. Concluding that these characteristics can be obtained once the band structure of the system is known we discuss as illustration the problems encountered with the two principal defects present in GaAs and related alloys namely the EL2 defect and the DX center.

Recent in situ applications of reflectance anisotropy (RA) to the study of the growth of 111-V materials by low pressure MOCVD are reviewed. These results illustrate the extreme sensitivity of the RA technique. During heterojunction growth the first 1-2 seconds are dominated by the change of group V species. Over the time scale of several minutes the signal exhibits damped oscillations correlated to the growth rate. An optical model is proposed to account for this behaviour. A difference in the optical anisotropy between growing and non-growing AsH3 stabilized InAs surface is observed. Large reflectance anisotropies during the growth of lattice-mismatched semiconductors are also presented. It is shown that these anisotropies are related to 3-dimensional growth. The beginning of the lattice-mismatched growth is quantitatively described by an optical model based on effective medium theories. More generally RA technique appears a very promising new method for in situ monitoring of epitaxial processes.

Simple donor and acceptor impurities in group Ill-V and Il-VI semiconductors are proposed to have at least two distinct structural configurations which differ by a few tenths of an eV in energy but which have very different electronic properties. The well known shallow-deep transition of donor levels in AlGaAs alloys associated with the DX center and the unusual properties of the EL2-related double donor arsenic-antisite defect in GaAs are intimately connected with the occurrence of such structural metastabilities. We suggest that processes similar to DX center formation inhibit the achievement of low resistivity p-type conductivity in ZnSe and lead to bistability of the Ga-antisite defect in GaAs. The phenomenon of impurity induced metastabilities in semiconductors has been a subject of interest for many years. In the last five years the pervasiveness of this phenomenon and its relevance to the understanding of the sometimes unusual electrical properties of impurities has become better established and understood. As a result, a coherent micoscopic description of the characteristics of several such metastabilities is beginning to emerge.

We systematically studied the Ga3d and A12p cation core level binding energies in molecular beam epitaxially grown GaAs/AlAs heterostructures by in-situ x-ray photoemission spectroscopy. The valence band offset v at GaAs/AlAs interfaces is found to be independent of the crystallographic orientation and determined to be 0. 44 0. 05 eV. Furthermore we found that the cation core level binding energies in the extreme vicinity of the interface are shifted by -0. 1 eV from their respective bulk values which clearly indicates that the charge distribution and the resulting band offsets have a transient over a distance of at least 2 monolayers from the heterointerface.

We describe the research activities of materials for optoelectronic device applications in China we laid emphasis on study of growth technology characteristics and physical mechanism of compound semiconductors with the structure of superlattice or quantum well by using home-made MBE or MOCVD systerms. Some performances of our optoelectronic devices based on these materials are also eseed

ihe (1 10) face in Ill-V binaiy compounds is a non-polar surface and allows the determination of valence and conduction hand edges as well as energy gap at the clean ultra-high vacuum cleaved surface. In epitaxial 111-V semiconductor multilayers this (1 10) face forms a cross section to the preferential 001 growth direction. With scanning tunneljng microscopy we have been able to observe the atomic arrangement in MBE-grown GaAs and A1GaAs layers as well in their interfaces. The binary and ternary cornpoupds can be clearly distinguished and we also find indications for composition fluctuations in the ternary. The atomic resolution images show that the material transition occurs over 2 unit cells. From the current-voltage characteristics across the GaAs-AlGaAs interface the valence band edge is determined and compared with theoretical calculations. The electronic valence band transition occurs over a length scale of less than 4 urn.

Strain induced band gap decrease and therefore enhanced near infrared absorption were demonstrated in the past with SiGe heterostructure receiver devices. Quasidirect transitions are expected for ultrathin SiGe superlattices because of zone folding effects from the superlattice periodicity. We report about experimental results from strained layer structures about device demonstrators and about device relevant theoretical predictions. Basic concepts of SiGe optoelectronic devices are explained and possible routes of integration with Si microelectronics are discussed.

The optical response of conduction electrons in a superlattice is presented. The time response of electron tunneling through a double barrier is examined with the time dependent Schroedinger''s equation. The energy states of a silicon quantuirt box are calculated with the use of a variational procedure for a spherical box. The regions of applicability of the band-model and the hoppingmodel for negative differential conductivity are discussed. And finally sonie problems involv ing phase rardoraization and inelastic scatterings with the presence of attractive o repulsive elastic scattering centers in a confined re gion are discussed.

As a result of the ever decreasing cost and increasing speed performance and integration level of Silicon VLSI the large scale use of high-speed GaAs digital IC''s will only occur if a dramatic decrease in cost occurs coupled with the attainment of a radiation hard-high performance technology. The larger scale fabrication of GaAs circuits allowed by the use of Si and SIMOX substrates will permit the attainment of such a low cost high reliability technology. In addition the present evolution of electronic circuits towards monolithic integration makes it very desirable to combine functions which are not attainable with devices stemming from only one material. The present paperreviews the recent material and device developments for GaAs on silicon and also extends the discussion to GaAs on SIMOX.

The paper reviews some recent developments in fabrication technology for nanoscale devices. The latter require a combination of high resolution lithography shallow electrical contacts and highly controllable patterning techniques. The main objective to be met is a precise geometrical definition of the structures (at the nanometer scale) without loss of electrical performance. Applications are discussed in the field of ultra-submicron HEMTs and resonant tunneling devices.

An external electric field perpendicular to the plane of the layers of a semiconductor superlattice induces a localization of the eigenstates and a quantization of the energy spectrum. These effects which correspond to the Wannier-Stark quantization are not only remarkable from the point of view of basic physics but they are also potentially important for different applications in optoelectronics. Indeed the superlattice electro-absorption spectrum exhibits both a blue shift associated with the decoupling of the quantum wells and at very low field a red shift associated with the existence of transitions oblique in real space between states localized near adjacent quantum wells. Both effects have been observed at room temperature and have led to promising device performances.

The spatial separation of electrons and holes in n-i-p--i doping superlattices results in large built-in space charge fields and low recombination rates. Due to the long recombination lifetimes a high density electron hole plasma can be generated by extremely low power optical excitation. This electron hole plasma induces large changes of the optical properties first by excitonic screening and band-filling and second by reduction of the space charge fields. The amount of the non-linearity of a typical n-i-p-i crystal may excceed that of bulk or multiple quantum well semiconductors by many orders of magnitude. In this paper we emphasize on further improvements of the genuine favorable non- linearities of n-i-p-i systems by using "hetero n-i-p-i" systems and by applying an external reverse bias by means of selective n- and p-type contacts. Thus, the changes of the optical properties can become even larger. Also, they depend almost linearly on the optical power within a wide range. Finally, the recovery time can be externally adjusted within the range from sub-nanoseconds to seconds, a property which is of particular significance for photonics. Some examples for the application of the nonlinearity and optical bistability of n-i-p-i superlattices will be discussed.

STRACT Dry etching techniques such as reactive ion etching (RIE) have found wide applicability in the fabrication of optoelectronic devices. However as requirements on device performance become more stringent and as devices incorporate the low dimensional quantum wires or dots issues such as materials selectivity controlled etching through thin layers fidelity of pauern transfer and etch-induced damage assume greater importance. This paper reviews recent work on the assessment of etch-induced damage including cathodoluminescence of multiple quantum wells and Raman spectroscopy. In addition to ion beam-induced damage created in the substrate chemical modification of the etched surfaces may compromise optoelectronic device performance. Some low-damage dry etching alternatives to RIE are discussed such as radical beam/ion beam etching (RBIBE) and thermally enhanced etching.

This paper deals with growth of GaAs InP and their ternaries quaternaries and heterostructures by the gas-source molecular beam epitaxy (GSMBE) method. Epilayer qualities are discussed and compared with those obtained by other methods. Some problems related to growth of layers and interfaces are discussed in detail. Properties of lasers photodetectors and optical modulators fabricated by GSMBE are presented.

In the 1990s increasing emphasis will be placed on improving OEIC capabilities by better understanding semiconductor crystal growth processes and by monitoring and controlling semiconductor crystal growth in real time. The noninvasive nondestructive characteristics of optical probes makes them particularly attractive for these purposes. Here I briefly discuss optical approaches directed toward achieving these goals and present some examples that illustrate work in this area currently being done at Beilcore.

The development of new epitaxial techniques has given rise to a variety of novel material combinations. Pseudomorphic combinations where the partners have lattice constants which differ by more than 1 are currently being extensively studied. The built-in strain can alter the symmetry and magnitudes of the band gaps concerned. Interesting examples of systems currently being investigated are strained layer superlattices based on Si/Si ixGex GiAs/lnAs and InSb/InSb ixA5x. The growth and properties of narrow gap semiconductor systems are reviewed together with their use as components for strained layer structures. The materials discussed are InSb InAs the alloys of these two compounds and alpha tin. The alloy system InAsiSb is prone to metallurgical problems such as ordering and phase separation in the mid alloy range but high mobility samples have been grown. Other alloy systems are also affected by similar problems. The strain associated with the small but significant mismatch between alpha-tin and InSb stabilises the alpha phase up to 100C and opens up an energy gap of 0. 2eV. The first observation of the Shubnikovde Haas effect with this heterostructure system demonstrates the presence of a high density twodimensional electron gas at the interface. The carrier density is too high to arise solely from the band offsets. Spike-doped and n-i-p-i structures are studied in InSb and InAs. Minimal dopant diffusion is found and highly non-linear optical absorption and a striking Quantum

Epitaxial methods allow the fabrication of nonlinear interferomethc structures which include the mirrors and the GaAs Multiple Quantum Wells (MQW) nonlinear medium in a single crystal. This results in very compact nonlinear microcavities with typically 5im overall thickness. Optical bistability is observed in these structures at mW optical power. We review our latest experimental results on these structures including the observation of high contrast switching in the reflection mode the direct measurement of dispersive optical nonlinearities in MQWs evidencing their saturation behavior at high intensities. Finally we report external-beam switching experiments which allow to assess the potential of these structures as all-optical gates.

IT-VT superlattices formed with CdTe and a zero-gap mercury based compound have been termed ''Type III" heterostructures. They can be either narrow band-gap semiconductors or semimetals depending on layer thicknesses and temperature. We shall report cyclotron resonance measurements on high electron mobility HgZnTe-CdTe and HgMnTe-CdTe superlattices grown by molecular beam epitaxy. The theoretical analysis of the data leads to an accurate determination of the electronic properties of these new infrared materials (superlattices bandgap as a function of the temperature temperature induced semimetal - semiconductor transition electron mass anisotropy exchange interaction in the diluted magnetic semiconductor superlattices. . . ).

Numerous potential excimer laser processing applications have recently been reported in the literature but examples of large scale excimer laser use in an industrial environment are very rare. In this article we inform about the different techniques and also about one of the first processes in which excimer lasers are used in a production line: Via-holes with aspect ratios close to one used in a printed circuit board of a high density multi-chip module are generated by ablation of the dielectric layer in an extremely reliable and reproducible way. The important processing parameters will be discussed.

A new reflectance anisotropy (RA) spectrometer is presented. The numerous similarities with phase modulated ellipsometry (PME) are emphasized. The RA spectrometer takes advantage of the high frequency modulation (50 kHz) provided by a photoelastic modulator. Moreover as compared to other techniques, this RA spectrometer allows the determination of both the real and the imaginary part of the RA signal. The use of optical fibers in both optical arms allows an increase of the compactness of the spectrometer. The adaptation of RA to a MOCVD reactor is described in detail. Four detectors can be used simultaneously providing the real-time spectroscopic capability. The numerical data system of the detected signal is based on the use of a high precision analog-digital converter and a fast Fourier transform processor. Moreover, on-line relations between the data acquisition system and external analog signals and triggers are available. Thus it can be inferred that this reflectance anisotropy spectrometer appears a useful tool for high sensitivity optical measurements and in situ control processing.

Semiconductor lasers have been successful in covering only a limited portion of the desired spectral regions. New non-linear optical materials based upon semiconductor quantum wells and artificially structured materials greatly enhance the non-linear susceptibility and create possibilities for both new devices to reach these spectral regions and novel structures which can be integrated with the existing lasers. Second harmonic generation with asymmetric quantum wells and approaches for phase matching are described. The potential to extend these concepts into the visible spectral region are also discussed.

Undoped GaSb epitaxial layers have been grown on (100) GaSb and GaAs substrates by low pressure MOCVD. It was found that the layer morphologies were strongly dependent on TMSb/TEGa (V/Ill) ratios. The mirrorlike surface can be easily obtained under V/Ill ratio in the range of 68 at growth temperature 600 C and growth pressure 100 torr. Beyond this range the surface deteriorated seriously. The epilayers were characterized by electron diffraction patterns and photoluminescent measurements. The boundexciton (BE) peaks and strong acceptor band peak in PL spectra were observed from the sample grown under V/Ill ratio of 6. 84 on GaSb substrates. PL peak intensity was found to be a function of the V/Ill ratios. When V/Ill ratios increased beyond the range of 68 the BE peaks disappeared and PL spectra became roughened. The full width at half maximum (FWHM) of acceptor-band peaks in PL spectra was dependent on V/Ill ratios ensuring that obtained from the analysis of surface morphology. IV characteristics of the pn diodes fabricated on the sample of undoped-GaSb/GaSb:Te was measured. The electrical properties of undoped GaSb were studied from the epilayers grown on GaAs semiinsulating substrates. The hole concentration increased and mobility decreased with growth temperature between 520 and 635C under V/1116. 84. For 550 C grown epilayers: as V/Ill ratio increased above 6. 64 or decreased below 6. 64 the hole concentration increased and hole mobility decreased. .

Time resolved luminescence experiments performed on GaA1As-GaAs-A1As nonsymmetric modulation n-doped thick Quantum Wells show an atypical behaviour regarding similar but symmetric ( GaA1As-GaAs-GaA1As ) Quantum Wells. In the latter system the luminescence has the standard radiative lifetimes in the range reported in the literature. Much shorter lifetimes for nonsymmetric Quantum Wells are a clear indication that a non radiative mechanism is associated with AlAs- GaAs interface. The temperature dependence ofthe lifetime and magneto-optical experiments suggest the existence of a non-radiative level 5 meV above the third electric subband of the Quantum Wells. Transfer ofcharge from GaAs ( F point ) to AlAs ( X point ) is proposed as a mechanism to shorten the lifetime ofthe luminescence process in agreement with theoretical calculations. 1_

Infrared photoexcitation of a SI GaAs sample generates photocurrents whose kinetics are interpreted in terms of photogeneration and thermal decay * * of the metastable state EL2 . The thermal deexcitation rate of EL2 is measured in the temperature range (240 K T 360 K). We demonstrate its thermally activated origin and we obtain : r 3. 3 lOt'' exp - O. 30/kT. Picosecond pulse and probe experiments are performed on the same sample. We observe an optical memory effect related to the optical generation of the * metastable state EL2 at room temperature. This effect persists over more than 10 ns.

The repartition ofnonradiative recombination centers density in a quantum well has been tested by timeresolved luminescence in samples containing an InAs plane inside a 16 nm wide GaAs well in Ga7AL3As. The results show unambiguously that more non radiative centers are located near the first grown interface. The non radiative carriers lifetime () vary between 4 ns when the InAs monolayer is close to the inverted interface and 8 ns when it is near the direct one.

Systematic comparative studies of the optical properties in the excitonic energy regime of MBE-grown ZnTe/GaAs and ZnTe/GaSb epilayers are presented. For these different substrate materials we investigate the influence of strain between layer and substrate the possible incorporation of impurities the electronic structure of the impurity-related exciton complexes and biexciton recombination processes at high-density excitation.

A rapid thermal CYD reactor has been employed for the deposition of silicon carbide layers on silicon. Stoichiometric SiC layers were deposited using silane/propane gas chemistry over the temperature range 720-970C. The process wafer was ramped rapidly to the deposition temperature after gas flows were established. The deposition was thus temperature activated so that minimum thermal budgets were obtained. The influence of both process pressure and the silane/propane gas flow ratio on carbon and oxygen content in the films was determined. The critical conditions for the deposition of stoichiometric silicon carbide with minimum oxygen content and without an interfacial oxide layer have been determined. In-situ doping with phosphine has been employed to deposit SiC layers with a phosphorus concentration of 5x1020cm3 and a resistivity of O. 6ohm. cm. Heterojunction silicon bipolar transistors were fabricated with deposited SiC layers for the emitters. While some enhancement was obtained for transistors with oxygen contaminated emitters those with purer emitters had common emitter gains of less than unity. This has been attributed to a reduction in base lifetime due to a carbonisation tail.

Silicon carbide is an interesting high-temperature large band gap semiconquctor. it ispromising as a basical material for optoelectronic devices . The optical properties of SiC have been studied by several authors. The absrption coefficient of SiC 6H3 has been measured by Choyke and Patrick up to 4.9 eV and by Makarov to 5.8 eV. Reflection spectra of 6H, 15R, and 3C SiC in the range 3.0 to 13 eV have been stidied in . The optical constants of SiC 6H have been measured by reflectivity in the range 4 to 25 eV, The energies of direct optical transitions between subbands in the conduction band, resulting from confinement in a one dimensional superI,at,,tice, have been measured in8sveral polytypes of SiC by absorption ' and electroreflection (ER) ' The electron energy band structure (85) of SiC of1he1 halerite structure (3C SiC) has been calculated by several 1tu4r2 ' . BS of wurtzite modification of SiC have been calculated 1 in ' ' ' for 2H iC. BS of 4H and 6H SiC has been calculated by the semiempirical pseudopotential method at high-symmetry points of the Brillouin zone (BZ). Tight binding calculations of 2H SiC show valence bands which agree with experiment, but unrealistic conductive bands due to the restriction to nearest neighbours in the Hamiltonian matrix In this work we report the electroreflectance (ER) spectra of hexagonal (4H and 6H) and cubic SiC measured in the range 1.0 to 5.6 eV. Values of direct optical gps1ave been obtained from the ER spectra using a multiple oscillator model ' . BS of SiC has been calculated by the first-principles self-consistent linear muffin-tin orbital (LMTO-ASA) method (2H, 4H, and 6H SiC) and by the semiempirical pseudopotential method (3C SiC). Calculated BS parameters have been compared with experimental data measured in this work and those available in the literature.

The methode of luminescence modulation consists of a superposition of cw X-ray excitation and a short pulsed UV-light excitation. Making use of an excimer laser as UV source and a spectroscopic array detector with wavelength and time resolution it is possible to make sensitive short and long term characterisation of X-ray produced radiation damages within scintillator materials. Preliminary results of different doped and undoped materials will be presented and compared with results of conventional luminescence measurements.

Thin low doped GaAs layers were deposited on Si(100) substrates using molecular beam epitaxy (MBE). The samples were investigated by nondestructive Far Infrared (FIR) Fourier Transform Spectroscopy. A new evaluation method was employed in order to obtain the phonon parameters the layer thicknesses as well as the densities and mobilities of the carriers. This method was successfully applied for layer thicknesses as low as O. lprn and carrier concentrations of about 2 . 1O''6cm3.

The Er-related two peaks at 1. 54im and O. 99pm were observed by applying dc voltages to the Er-implanted InP layer. These peaks were assigned to the intra-4f transitions of Er3+ from I13/2 to ''15/2 and from I11/2 to I15/2 respectively. No other emission bands were observed in the wavelength range from 0. 8 to 1. 6/tm. The emission characteristics and the fine structure of the l. 54im emission spectrum were discussed in comparison with those of photoluminescence.

We show that electronic Raman scattering measurements of the intrasubband plasmon dispersion in a GaAs/A1GaAs heterojunction is a viable contactless optical method for the determination of sheet carrier density of the two-dimensional electron gas. We demonstrate non-persistent optical control of the carrier density by a dynamic charge transfer effect: from Raman measurements of the plasmon we directly determine the change in carrier concentration with excess illumination.

The local thermodynamic equilibrium as well as the non-equilibrium properties of crystal defects in semiconductors are discussed with emphasis on such configurations that allow for multiple ionization and electronic excitation. A system of rate equations is developed which describes the temporal change of the occupation numbers of the different energy levels; it includes the processes of free charge carrier capturing as well as thermal emission. The results of the investigation can be used, for example, to obtain a more realistic dynamic description of the occupation of the chromium induced energy levels in gallium arsenide which play an important role as recombination centers in material for fast photonic switching.

Si/Ge superlattices provide the possibility to create a novel direct band gap semiconductor. The energies and oscillator strength of interband transitions are strongly affected by strain individual layer thicknesses and superlattice periodicity. We report on photoreflectance (PR) studies of SimGen superattices with a layer thickness ratio m/n1/3 and period lengths of 8 12 and 16 monolayers. Between 1. 9 and 2. 5 eV transitions which are related to the E1 gap are observed for all samples. In the infrared region between 0. 9 and 1. 2 eV superlattice induced interband transitions are observed for Si2Ge6.

STRACT We use Raman scattering to investigate direct gap Si/Ge superlattices for which the Si layers are in the form of biatomic sheets. We find a characteristic signal arising from the presence of the biatomic Si sheets. A range of samples have been investigated and 3-dimensional lattice dynamical calculations have been performed which pinpoint the Si layers as the origin of the signal. We illustrate how the signal may be used to characterise the quality of for example (Si)2/(Ge)6 superlattices grown at various substrate temperatures.

The Sputtering-Assisted Plasma (SAP)-Chemieal Vapour Deposition (CYD) method was used to prepare in a gas mixture of SIH4 + Ar + H2 a-Sii_Ge : H with different composition and optical gap between 0. 98 and 1. 85 eV. From experimental study of samples optimal processing conditions were obtained and a model of interactions between H and the growing surface was presented. Study of the properties of samples shew that hydrogenated a-Si Ge alloy prepared by SAP-CVD technique is superior in some respects with regard to optoelectronic effect and deterioration of the performance related with in-crease of Ge content.

A hybrid growth of GaAs on Si combined molecular beam epitaxy (MBE) with subsequent liquid phase epitaxy (LPE) has been carried out to fabricate light emitting diodes (LED''s) on Si. The formation of the dissolution pits which was a serious problem for this method could be suppressed by making the formation mechanism clear. The optimum hybrid-grown GaAs on Si had better crystallinity than MBE-grown one. It was also suggested that further improvement in the crystallinity of MBEgrown GaAs layers led to higher quality of hybrid-grown ones. LED''s have been fabricated using the optimum hybrid-grown GaAa-on-Si substrates. They had higher potential to achieve high light intensity and stability compared with those fabricated by MBE-grown ones. The better characteristics are attributed to higher crystallinity of the hybrid-grown GaAs on Si.

We report on InGaiAs/GaAs single quantum wells grown at low substrate temperatures in a wide range of indium compositions (x) and well thicknesses. Compared with ordinary growth conditions the transition between pseudomorphic and relaxed regions (in the epilayer thickness versus x plane) occurred at higher indium compositions when the growth temperature was lowered. An increase in critical thicknesses for pseudomorphic growth by at least a factor of seven for alloy compositions with less than 40 indium was observed. This was determined by low temperature photoluminescence spectroscopy and transmission electron microscopy measurements. Results of studies on the thermal stability of these quantum wells are also presented.

Two different versions of hotwall--epitaxy reactors were used to grow ZnSe and ZnTe layers. In the first type of hotwall epitaxy reactor Zn and Se were evaporated seperately from elemental sources. By changing the Zn/Se ratio in the gas phase we could alter the growth direction of the ZnSe layers from 111 to 100 Raman spectroscopy proved the existence of a Ga2Se3 layer at the GaAs/ZnSe interface. In the other HWE reactor stoichiometric ZnSe and ZnTe were used as source materials. Photoluminescence and Xray rocking curves proved the high quality of the epilayers. The rocking curves showed a full width at half maximum of 75 arcseconds for ZnTe.

We report on our progress of Il-VI and IV-VI compound semiconductor heteroepitaxy on Si(1 1 1) and (100) substrates by MBE. A stacked buffer layer of CaF2 SrF2 and BaF2 serves to overcome the large lattice and thermal expansion mismatches between the different materials. Undoped and Sb-doped epitaxial CdTe on Si(100) layers exhibit superior surface morphologies and photoluminescence spectra when illuminated with an Ar-laser during growth however dopant activation is much less pronounced as compared to work performed on homoepitaxial CdTe layers on CdTe(100) substrates. 3 im thick PbTe and PbiSnSe layers deposited on fluoride covered Si exhibit x-ray line widths as low as 150-200 arc sec and their mechanical thermal mismatch strain is fully relaxed at room temperature. Up to now growth of epitaxial Il-VT and IV-VI layers of reasonable. quality directly on Sisubstrates using any technique has not been reported. This is because of the high lattice and thermal expansion mismatch between the different materials as well as because of chemical compatibility. Growth of good quality layers has been reported only with an appropriate buffer layer. We have found that group ha fluorides namely CaF2 SrF2 and BaF2 form such a buffer and have been able to grow for the first time high quality epitaxial Il-VI materials (CdTe [1 as well as IV-VI materials (PbSe [3] PbS [4] PbTe Pbi SnSe [5-7] and Pb1EuSe [8]) on Si-substrates. IRsensors were

Strained semiconductors offer an additional degree of freedom in the tailoring of material properties. The growth of strained layers particularly for large degrees of misfits by techniques such as MBE and MOCVD are not particularly well understood. In the case of biaxial compressive strain it is apparent that above 2 misfit growth proceeds in a 3-D island mode. Biaxial strain in pseudomorphic structures dramatically alters the bandstructure. As a result the transport and optical properties are changed. The properties of strained MQW lasers modulators and MODFETs will be described and discussed. I.

We report the results of calculations of the optical properties of strained InGaAs/InP quantum wells based on realistic band structure. Emphasis is placed on those features relevant to the operation of quantum well lasers. A k. p model including spin and strain is used to calculate the electronic states of the quantum well. The optical matrix elements as well as the dispersion of the conduction and valence subbands are obtained directly from the model and used to calculate gain and spontaneous emission spectra to study some aspects of intervalence band absorption and to model the behaviour of multiquantum well lasers. The results show that interband mixing causes substantial departures from the predictions of simple models including the failure of band edge selection rules for optical transitions. It is demonstrated how the combined effect of alloy composition spatial confinement and strain can can be used to influence the optical properties of quantum wells and improve the performance of lasers based on these structures.

The critical layer thickness (CLT) for InxGaixAs/GaAs has been studied by photoluminescence transmission electron microscopy and reflection high energy electron diffraction with the composition x and growth temperatures as parameters. The obtained values of CLT have been compared with theoretical models. None of them coincide with the experimental results. For x 0. 3 the CLT varies rapidly with x while the dependence is slow for x 3. Here the CLT is small typically a few monolayers. The CLT is governed by dislocation generation for x 0. 3 and by the onset of three dimensional growth for x 3.

GaP/InP strained-layer superlattices (SLS) grown on GaAs substrates are a novel structure with a large lattice mismatch symmetrically shared (+ 3 . 7 (GaP) -3 . 6 (InP)). We present growth and characterization of two types of GaP/InP based heterostructures: i) isolated SLSs and ii) a SLS based QW confined by A1GaAs barriers. Growth by Atomic Layer MBE has allowed to combine P- and As-containing materials in a controllable way preserving flat interfaces at low substrate temperatures. Optical characterization oftheheterostructures ispresented and correlated with akp model obtaining the first estimation for the conduction band offset at the GaP/InP heteroj unction. All superlattices studied have been found to be spatially direct (type I) being this feature very promising for their use as active layer in a semiconductor QW laser. I.

The electronic properties of heavily and orderly Si-doped nipi structures in GaAs are studied theoretically using the abinitio self-consistent pseudopotential method within the local density approximation. Two nipi configurations are considered. Besides investigating the nature of the impurity-related band edge states the xy-planar-averaged local ionic and self-consistent potentials are also analyzed. The screening effect of the host crystal on the doping induced potential is found to be small. The effects of the doping induced electric field and the strain due to dopings are also examined.

Epitaxial gallium arsenide (GaAs) films of controlled electrical properties are essential for the fabrication of high performance devices. Metalorganic vapor phase epitaxy (MOVPE) utilizing the reaction of trimethylgallium (TMGa) or triethylgallium (TEGa) and arsine (AsH3) is commonly used for the epitaxial growth of GaAs. The use of highly toxic AsH3 however is a serious hazard in research and manufacturing operations. In this work the MOVPE of device quality GaAs from elemental arsenic has been demonstrated for the first time thus minimizing a major safety concern. The reaction of TEGa and As on the substrate surface at 450-550C in a H2 flow was used. The parameter of the growth process and the electrical and photoluminescent properties of epitaxial GaAs are discussed. Further TMGa TEGa and arsenic show strong absorption in far ultraviolet. The epitaxial growth of GaAs films can be achieved at low substrate temperatures by irradiating the gaseous reactant with a UV laser. Epitaxial GaAs films have been grown at 425C or higher by using ArF laser enhanced reaction of TEG and As. The electrical and photoluminescent properties of these films have also beencharacterized. Epitaxial GaAs films grown by the laser enhanced process have been found to contain considerably higher carbon concentration than films grown by the thermal process. This is due presumably to the photodissociation of carbon-hydrogen bonds in TEGa.

Work in progress and completed studies in epitaxial liftoff by a number of workers in these Laboratories are reviewed. The areas include waxless chemical release on patterned substrates the liftoff of optical filters and of optical modulators for potential integration with silicon and the regrowth of unstrained films of arbitrary lattice constant on strained MBE grown InGaAs layers which have been chemically released from the underlying substrate. An extremely strong excitonic absorption has been discovered in 1pm GaAs liftoff films and strain measurements on these films have given hydrostatic and uniaxial deformation potentials.

A method for reactive ion etching (RIE) InP has been developed using CH4/H2 which allows the fabrication of dots of 6Onm diameter and 200nm height with good aspect ratio. The effect of the etch on the optical quality of the InP surface is investigated by phonon Raman scattering and 5K luminescence.

Several important techniques for fabricating micro-cavity semiconductor lasers including surface emitting lasers have been developed. Reactive ion beam etch (RIBE) for GaA1As and GaInAsP is employed and its condition for vertical fine etch under low damages and removal of residual damages are made clear. Passivation by sulfur is introduced to the fabrication process. Regrowth techniques for DII structures by LPE and MOCVD has been established. Some device applications are discussed. 1. MICRO-ETCHING PROCESS Micro-cavity lasers including a vertical cavity surface emitting laser1 are attracting the research interest for optical parallel processing and parallel light wave systems. In order to realize micron-order or sub-micron laserdevices the technology of micro-fabrication must be established. In this study the total fabrication technology has been almost completed. First fine and low damage etching condition by ultrahigh vacuum background RIBE using a Cl2 gas has been made clear. We have found an isotropic etching condition for the vertical side wall formation and good mask traceability i. e. the acceleration voltage is 500 V and substrate temperature is 150 C with a 5000A thickness Si02 mask. Residual damages induced on the surface and the side wall are characterized by photo-luminescence and making stripe lasers. Figure 1 is the histogram of the nominal threshold current density for (a) oxide-defined stripe lasers (b) RIBE etched and LPE regrown BH-lasers using an LPE grown DII wafer (LPE/LPE) and (c) RIBE etched

Xanthone derivatives have been found to be new organic nonlinear materials with a high efficiency of second harmonic generation (SHG) and transparency in visible region. For example, 3-aminoxanthone had a high SHG activity (SHG emission of this sample was 1 3 times higher than that of urea ) and good thermal stability (mp=232 C ) . A single crystal of this sample was transparent above 430nm. The SHG properties for other xanthone derivatives were also investigated.

Synthesis and characterization of a class of chiral nonlinear optical organic materials viz. pyrrolo[1 with chiral molecular structure are presented. Both single crystals and crystalline thin films of la have been grown. Structural parameters have been determined by X-ray diffraction. Linear and nonlinear optical properties of the crystals have been analyzed. The transparency range extends into the near-UV-region. The nonlinear coefficients djjk have been measured by second harmonic generation (SHG) using the Makerfringe and phase match techniques.

A novel polymeric material a poly (methylmetacrylate) (PMMA) with 7 by wt. of poly (ethylenecovinylacetate) (EVA) blend is presented. The PMMAIEVA thermograph in the temperature range -50 to 220 C exhibits a phase transition at 50 C. During this transition the typical hysteresis of the polymeric transitions has been noted. We show the behaviour of the optical transmission as a function of the temperature and present some physical properties of this material. In the frame of a research on the preparation and characterization of high mechanical performances PMMA-based blends we conducted several optical tests in order to verify the potential applications of such blends in devices of integrated optics. Tough transparent PMMA is industrially produced by a multistage process of incorporation of rubbery particles in a methacrylic matrix. The rubbers are obtained by a suspension process in which a shell of cross-linked rubbery buthyl acrylate-styrene copolymer is polymerized around a PMMA matrix. The core-shell structure (fig. 1) is necessary in order to assume a good stress transfer between the phases and at the same time a better matching of the refractive indices of the two phases. To achieve the desired level of toughening high amounts (20-30 by wt) of rubber are necessary with an unavoidable diminution of elastic modules. In our procedure an amorphous ethylene-co-vinylacetate copolymer (EVA 20 by wt of VA) is used as rubbery component 1 The synthetic process

Strong second harmonic generation (SHG) has been obtained from multilayered LangmuirBlodgett (LB) films of (i) a new hemicyanine dye ENoctadecyl--4-''(4-diirtethylaminophenyl) ethenyl)pyridinium iodide interleaved with 4 4 ''dioctadecyl--3 5 3 '' 5 '' -tetramethyldipyrrylmethene hydrobrornide and (ii) an unusual irbridged donor-acceptor zwitterion Z/3(Nhexadecyl4quinolinium) acyano4styryldicyanomethanide . The SH intensity increases quadratically with the number of LB layers. For the interleaved structure the SH intensity obtained from 200 layers (Ca. 0. 5 m thick) is 18 times the signal from a monolayer of the hemicyanine dye reported by Girling et al the intensity is the highest reported for an LB film.

Phase matched second harmonic generations (SHGs) in two kinds of poled polymer film waveguides are observed. Two kinds of dye dopants 2-methyl-4-nitroaniline (MNA) and Disperse Red 1 (DR1) are used for preparations of thin film poly-methylmethacrylate (PMMA) waveguides. The conditions for the collinear and the Cerenkov type phase matchings are realized at the thicknesses giving the same effective refractive indices for each type.

Single crystals of the nonlinear optical organic materials which cannot be crystallized by the Bridgman-Stockbarger method were grown in cores of glass fibers from solutions. These nonlinear optical fibers were used for the phase-matched secondharmonic generation due to Cerenkov radiation.

InSb and related ternary alloys have many potential applications in addition to the conventional one of infrared detection provided that near ambient temperature operation can be achieved. The growth by MBE of n-type and p-type InSb has been established using silicon and beryllium dopants respectively. Multilayer diode structures have been studied up to 300K in order to determine carrier generation mechanisms and examine concepts for ambient temperature operation.

We present the liquid phase epitaxy growth (LPE) of GaInAsSb/( 1 00) GaSb and InAsSbP/( 1 00) InAs near their miscibility gap (MG) boundaries. The conditions f or growing latticematched layers of optoelectronic quality are given. The cut-off wavelength limitations due to the MG are : 2. 4 p. m for GaInAsSb and 2. 6 p. m for lnAsSbP. As an example of application results are presented on LPE grown photodiodes based on these quaternary alloys. 1 -

We report the first observation of the carriers confinement and recombination in the adjusted quantum wells at the type II interface in GaInSbAs/GaSb heterostructures grown by liquid phase epitaxy. Type II heterostructures in which both the conduction and the valence band edges of one semiconductor are shifted upward relative to those of the other one can exhibit adjacent dual quantum wells for electrons and holes on the two sides of the interface. Tunneling-assisted radiative recombination between the wells offers an efficient, bias-tunable, source of radiation at below-gap energies.

Staggered-''lineup type II heterojunctions have been realized in Ga In As Sb solid solutions lattice matched. to GaSb as well as ones depending on alloy composition (x1 O. 23 or XinO8O)i n Unique features of type II heterojunctions due to carrier localization and spatial separation on the interface have been experixnen tally observed by electroluminescence generation of coherent radiation and photocurrent gain. Distinctive hallmarks of the narrow-''gap GaSbGaInAsSb heterojunctions have been considered in connection with CV 1-. V and spectral response experiments. Energy band schemes of such structures have been analized. GaSbGaInAsSb heterojunctions with x 0. 80 were found to be type II misaligned ones. Novel optoelectronic devices for midIR spectral range of 1 (lasers LID''s and high-. speed photodiodes) were developed on the base of GaSb-GaInAsSb heterojunctions.

The growth pattern of GaInAsfInP quantum wells on large area InP substrates has been investigated. Scanning Photoluminescence (sPL) performed at room temperature has been utilized to map the entire area of the wafers at a spatial resolution of 600x600j. tm. It will be shown that the local variation in energy shift of the quantum well luminescence is caused by variations in growth rate which matches the growth rate distribution in GaInAs bulk layers. The sPL data were compared to model calculations of the growth rate as a function of position on the wafer. Through the acquired insight in the growth process new process parameters could be chosen where not only the uniformity of quantum well thickness but also that of GaInAs bulk layers was substantially improved.

Ga As (x 47) epitayers tatticemismatched to laP and steptike composition tayers of InAs (O 61) were prepared by atmospheric pressure metatorganic chemical vapor deposition (MOCVD) with a horizontal reactor using trimethytindiu. m (TMIn) trimethylgalliu. m ( TMGa) arsine (AsH and phosphine (PH as the source materials. The alloy compositions were measured by the Electronic Probe (EP) and the XRay Diffraction (XRD) . The crystalline quality of the epilayer was detected by the Xray double diffraction and the composition depth profile of Ga. InAs/InAsP1 InP was measured by secondary ion mass spectrometry (SIMS)respectively. It indicated that the introduction of steplike composition layers was an effective method for decreasing the latticemismatch between layers and improving the crystalline quality.

Deep level transient spectroscopy (DLTS) and photoluminescence (PL) measurements are used to characterize short period selectively or uniformly Si-doped GaAs-AlAs superlattices (SLs) grown by molecular beam epitaxy at two different temperatures. DLTS measurements show the presence of DX center with an apparent activation energy of 0. 42eV and a trap concentration which decreases as the growth temperature is lowered. From an analysis of the DX concentration and binding energy we show that this center is mainly located in the AlAs layers. The high growth temperature enhances the silicon diffusion from the GaAs wells towards the AlAs layers which allows us to detect the DX even when only the GaAs layers are doped. The PL measurements performed on the near band edge show different transitions. No deep luminescence in the near infra-red spectrum is observed on these MBE layers despite the high DX concentration.

F IR spectr-a of PhTe and PbTe : Cr f i lra''s have beerL stud ied in the range ''30 ''5C)OO X ray invest igat ions of the f i Im irtci icated st. r-ained layers wjth high-pressure PbTe phases - c3eS- and CsCIt. ype. The frequenc ies of the irafr-ared modes in these h igh -pressure phases wet-c det. errniried from the spectra I depertderLces of the modulus of the d ie Iect. r ir funct ion $ a. nd the d ie lectr ic loss funct. ion IrnC 1 . . . '' ) and tentat ive Ly ass igned by sca I irLg of the corresporLcl ing SrtSe and I C C PbTe frequenc ies.

A novel method is demonstrated which allows to localize and clearly identify hot spots in integrated circuits with high spatial resolu-'' tion. The method is based on the optical beam induced current technique (OBIC) using a laser scanning microscope with infrared illumination. Due to the OBIC contrast thermal defects can be recognized in a difference image of two OBIC images measured at different background temperatures of the circuit. The method is applied to thermal mapping of a CMOS NOR-gate. Calibrating the OBIC signal in dependence on the circuit temperature the absolute temperature of the hot spot is deter mined.

We present a complete characterization study of GaAs/Si heteroepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) at 750C using the two-step method. High resolution transmission electron microscopy secondary ion mass spectroscopy deep level transient spectroscopy (DLTS) and photoluminescence (PL) spectroscopy have been performed to study the initial stage of growth misfit and threading dislocations Si diffusion and the deep levels in the GaAs layer. We describe the influence of GaAs/AlAs superlattices in the buffer layer on the decrease of dislocation density and on Si diffusion from the substrate and the existence of deep electron traps induced by the heteroepitaxy. DLTS reveals hole traps attributed to Si incorporation on the basis of PL measurements which could contribute to the reduction of the minority carrier lifetime. We also show an improvement of the layer quality by the use of selective epitaxy.

High energy electron diffraction is sensitive to details in charge and potential distribution since scattering occurs by the net charge or electrostatic potential. Several techniques have been developped for characterization the atomic and electronic structure at or near interfaces: convergent beam profiles critical voltage effect in electron diffraction reflection/refraction at interfaces. Appplications are shown to bulk semiconductors single interfaces and multilayers.

Simultaneous diffusion of Zn and Cd yields shallow and high doped pt_InGaAs layers. Using a closed ampoule technique an increa sing amount of CdAs2 in the Cd3As2/Zn3As2 source results in a decrea sing diffusion depth whereas a high hole concentration level can be realised. The experimental result of the simultaneous penetration of Zn and Cd atoms into the crystal can be understood on the basis of an interstitialsubstitutional diffusion mechanism.

The authors perform an analysis of silicon defect stncture as a function of irradiation dose based mainly on their infrared absorption data for neutron-damaged Si and the available literature results for neutron- and electron-irradiated Si . Remarkable correlations between Fermi level position in irradiated Si and at the silicon - (reactive and unreactive ) metal interface are presented and discussed.

InP epitaxial layers grown by MOCVD on InP GaAs and GaAs/Si substrates have been studied using photoluminescence (PL) photoreflectance (PR) and electroreflectance (ER) at different temperatures. PL measurements at 300K indicated the intensity of the band-to-band transition to bear a ratio of 5. 4:1. 8:1. 1 in the sequence of InP/InP InP/GaAs and InP/GaAs/Si samples. At 10K the PL spectra showed four clear features. The full width at half maximum of the free exciton transition were 5. 4 8. 8 and 10 meV for the samples in the same sequence leading to a direct measure of the epilayer quality. The peak positions were the same between InP/InP and InP/GaAs but a 8. 4 meV shift towards the lower energy was seen with the InP/GaAs/Si sample indicating the influence of the large difference in thermal expansion coefficients. The intensity and width of the acceptor-to- donor signal was found to be quite different among the three samples and the relation to the diffusion length and surface electric field were examined. The PR data revealed the bandgaps to be 1. 334 1. 325 and 1. 294 eV for the InP epilayers on InP GaAs and GaAs/Si substrates respectively. A broad shoulder-like peak 30 meV below the fundamental absorption edge was observed only for InP/GaAs/Si and hence attributed to some shallow level defects induced by antiphase disorder. Temperature dependence showed different bandgap temperature coefficients and

In conventional techniques of characterising traps and DX centres in ITT-v compound semiconductors (e. g. Deep Level Transient Spectroscopy Photo Induced Transient Spectroscopy Hall Effect Transient Spectroscopy) the transient or timedomain response of the traps at various temperatures is investigated. Recently a number of researchers in the field including the author have presented a frequencydomain study of the same problem. The advantage of this alternative approach is that it allows one to use the actual device to study traps (unlike the conventional technique where the measurements are carried out on other structures ) . In this paper the theory of the frequencydomain approach is presented with emphasis on microwave devices and a simple experiment based on the theory is described. It is also shown that the same physical concept can be employed to study traps in optical devices.

The dispersion of'' occupied and unoccupied electronic states normal to the surface of clean Ge(OO1) 2x1 surfaces is investigated by angleresolved vacuum UV photoemission using synchrotron radiation. Spectra are taken not only at constant photon energy in the energy distribution curve (EDC) mode but also in modes where the photon energy is scanned to obtain spectra at constant initial state energy (CIS) or constant final state energy (CFS). The results are compared with different bulk band structure calculations by means of electron transition plots (ETplots) where final state energies of observed peaks are displayed as a function of the corresponding initial state energies.

GaAS I AIGaAs multiple quantum well structures grown by low pressure metal organic chemical vapor deposition have been studied using electron microscopy photoluminescence photoabsorption and photocurrent spectroscopies. Room temperature exciton doublets quantum confined Stark shifts were observed and analysed.

(In this paper we propose a model based on plasma oscillations theory of solids for the calculatio f th average energy gap of optoelectronic materials having A B-''- 1C2 chalcopyrite stru eture. In the present calculation special care of delectrons in the case of noble and transition metal compounds has been taken into account. Our calculated values are in excellent agreement with the reported values). The dielectric theory of Phillips1 Van Vechten2''3 and Levine has been widely used in a varity of physicochemical problems relating to crystal structures nonlinear optical susceptibilit ies dielectric constant cohesive energies heats of formation average energy gaps etc. Using the concept of these theories the author 5 has recently developed a model based on plasma oscill ations theory of solids for the calculation of the covalent (Eh)afld ionic (C) energy gaps of several semiconductors having different crystal structures. . In the present paper we extend the calculation of the average energy gap in the case of AIBIIIC2VI semiconductors. The expressons for the Eh and C in terms of plasmon energy can be written as7 Eh K1 (tw)L6533 eV (1) C K2b (!iw)2" ex [ K3(hw)" 3 ] eV . (2) If delectrons are present in the crystal following relationhas been developed for the ionic energy gap while the covalent energy gap remains the same. C Kb (w)2" exp [K5 (''hw) (hw)2" 3J eV () where K''s

For a-Si1 C :H samples prepared with /([CH4J + [SiH4J) ratios of 0. 1 0. 2 dxO. 25 the density of deep states has been investigated by means of post-transit-time photocurrent analysis and thermally stimulated conductivity. Both techniques yield results which are in good agreement and show a localized states density which rises towards midgap.

We report calculations of the optical absorption coefficient for interband transitions in a superlattice subject to electric and magnetic fields parallel to the growth axis. We show that in a two-band model the absorption spectrum is a sequence of resonances with a structure that can be simple or very complex depending in a sensitive way on the ratio between the magnetic and the electric energies. We discuss the case of GaAs/A1GaAs superlattices using a six-band model in the envelope function formalism. For this system we show that the two-band parabolic model may only be used at low magnetic field.

Semiconducting FeSi2 thin layers have been grown on Si(111) by solid state reaction under UHY conditions. The different reaction steps in the temperature range 380 750C were followed in-situ by Auger Electron Spectroscopy (AES). FeSi2 is formed between 550 and 680 C. The low energy excitation spectra of the thin FeSi2 layers were measured by High Resolution Electron Energy Loss Spectroscopy (HREELS). Surface phonon excitations at 50 meV energy are observed and explained in the framework of dielectric theory of surface scattering. The presence of the Fuchs-Kliewer surface phonons in the HREELS spectra gives evidence of the semiconducting character of the FeSi2 overlayer. In the higher energy range a broad loss structure occurs corresponding to the excitation of electronic interband transitions. The onset of this structure at 0. 8 eV gives an indication of the band gap energy of the silicide. Its intensity together with the small experimental q11 transfer is an evidence of a direct band gap for the FeSi2 layer.

A model of one-electron states is developed for the energy levels of substitutional chromium ions in GaAs. This strong-crystal field approach allows for t2- and e-type states of the ions Cr4(d2) Cr3(d3) Cr2(d4) and Cr(d5) in a Td environment. A great deal of the reported experimental evidence can be reconciled in a uniform picture by taking into account donor- and acceptor-like processes and internal transitions of these oxidation states. These deliberations are supported by cryo-temperature cathodoluminescence measurements in the near-infrared range.

The low temperature photoluminescence of ultra pure GaAs grown by vapour phase epitaxy was investigated .The free exciton luminescence spectnim of GaAs is described in the framework of the polari ton theory . An inf luence of the excitation density and temperature on the polariton luminescence 1 ineshape was studied . Temperature transi tion from the case of the strong exci ton-photon coupi ing to the case of the weak ex citon-photon coupl ing was observed . An opportunity of use of the polariton luinines cence 1 me shape analysis for characterizat ion of pure GaAs crysta 1 s is demoristra ted.

We report a detailed study of GaAs/A1GaiAs double-barrier quantum wells grown by molecular beam epitaxy. In these structures the GaAs layers were embraced by thin AlAs barriers and then by Al033Ga067As outer barriers. It is shown that the insertion of one or two monolayer AlAs barriers has spectacular effects in changing the confinement energies. Numerical calculations have been performed within the envelope function approximation including the exciton corrections. The observed emission peak energies in low temperature photoluminescence spectra are in good agreement with the calculation values.

Microwave absorption in GaAs and influence of hot charge carriers on formation and dissociation prcxeses of xund states was studied. I'1k investigated classical cyclotron resonance in pure GaAs epitaxial layers. This made it ible with tt lp of contact I method to determins a norecjilibrium electron mobility . Smooth decreasir of exciton 1umirscence with inoreasir of microwave power was observed and a model describir this ptnomenon was suggested.

Semiconductor doped glasses have been studied by small angle neutron scattering. The results allow a precise determination of the average size of the microcrystallites and to evidence the volume depleted of semiconductor costituents that sorrounds each particle

For our studies of laseractive rare earth ions in dielectric optical waveguides we have implanted Nd and Er ions into x and zcut LiNbO3 single crystals. We show the recrystallization of the host and the rare earth diffusion during annealing. Nd and Er have different solubilities and different diffusion constants in LiNbO3. The solubility is strongly temperature dependent. The diffusion is substitutional fastest parallel to c-axis of the LiNbO3 crystal and characterized by an activation energy of approximately 3. 6 eV.

Tertiarybutylarsine (TBAs) was utilized in the fabrication of GaAs A1GaAs and GaAs/A1GaAs structures in a Low Pressure - Metal Organic Vapor Phase Epitaxy (LP-MOVPE) system. Good quality epitaxial layers were achieved at 700 C with V/LI! ratio of 50. Undoped GaAs and AI (x 3-0. 6) layers were p-type with typical background carrier concentrations of mid 1014 cm3 and 1016 cm3 range respectively. Carbon could be used as p-type dopant in A1GaAS layers by controlling the TBAs mole fraction. Double-heterostructure lasers were fabricated and showed a threshold current density of 500 A/cm2. GaAs/AlGaAs multiple quantum well structures produced photoluminescence spectra with very narrow FWHM comparable to arsine-grown samples. Electro-absorptive waveguide modulator with MQW active layer demonstrated more than 2: 1 modulation ratio at the energy far below the QW exciton absorption peak. The deposition of 111-V compound semiconductors by metalorganic vapor phase epitaxy (MOVPE) is normally accomplished with gaseous group V precursors. These sources arsine (AsH3) and phosphine (PH3) are highly toxic and are stored in high pressure cylinders. Thus careful handlings are required to avoid accidental leakage. Lately a number of less hazardous arsenic compounds have been investigated as alternative As sources Methyl ethyl and butyl groups are substituted for one or more of the hydrogen atoms in arsine. In particular Tertiarybutylarsine (TBAs) has been most successful in growing high quality GaAs and A1GaAS films and useful electronic devices have

Complex spectroscopical and piezospectroscopical investigations of system ZnCdi-Se used in laser cathode-ray devices were realised in the whole composition range 1 . Westudied the luminescence features connected with excitons localized by potential fluctuations caused by both compositional and structural disorder and also the influence of elastic stresses on the properties of the laser screen. Solid solutions of semiconductors are weakly disordered systems in which the disorder involves composition fluctuations and therefore crystal potential field fluctuations. In ideal solutions of this kind the arrangement of the substituent atoms at sites of the relevant sublattice is a random one. They include ternary direct-gap Il-VT materials based on zinc and cadmium chalcogenides with substitution in the cationic sublattice. These systems can exist with any ratio of the components and their electronic properties (band gap valence band splitting energy) vary smoothly with the composition. For 11-VT materials where the excitonic states have large radii(a 3- lOnm) the most probable interaction is whith large-scale composition fluctuations having dimension R a . A theoretical treatment 2 shows that such an interaction causes both localization of excitons by large-scale composition fluctuations forming a density tail of localized excitonic states in the band gap which create the long-wavelength part of the absorption line and scattering of delocalized excitonic states which create the short- wavelength part of the absorption line. The fluctuational disorder causes a composition dependent broadening of the

Highly anisotropic polytellurides MTe with M Zr and x 1. 5 to 5 have been synthetized under thin film form for the first time. Preferential orientations of these films with respect to the substrate surface are evidenced and tentatively correlated to the anisotropy of the optical or conduction properties.

Buried Ridge Structure GaInAsP/InP lasers with stripes parallel to and directions are fabricated by metal-orgnic vapour phase epitaxy regrowth and effective carrier lifetimes Teff of these devices are determined from the variation of the turn-on delay of the emitted radiation when short current pulses are applied to the lasers for different bias currents. We obtained Teff 2 ns for stripes parallel to the direction and eff lfl the range from 0. 5 ns to 0. 7 ns for stripes parallel to the direction. Our results demonstrate that the earlier observed large threshold currents of lasers with stripes parallel to the direction are essentially due to reduced carrier lifetimes and to a minor extent due to additional leakage currents. The reduced effective carrier lifetimes are attributed to Zn which has diffused from the GaInAs-contact layer into the active layer in accordance with recent secondary ion mass spectroscopic investigations. The reduced carrier lifetime leads to an increase of the 3 dB cut-off frequency of directly modulated lasers beyond 6 GHz. SPIE Vol 1361 Physical Concepts of Materials for Novel Optoelectronic Device Applications 1(1990) / 917

In n-type GaAs/Gai. xAlxAs single double and multiple quantum wells continuous oscillations in the current occur when electric fields in excess of a few hundred volts cm1 are applied along the layers. The frequency of the oscillations increases with the electric field and the electron concentration over a range of frequencies up to the gegahertz region. A strong electroluminescence (EL) signal is observed at and above the threshold field of the instabilities. The intensity of the EL signal increases with electric field as ''EL Fs where s is typically s 5. The EL spectra peaks at an energy close to the PL spectra. EL is shown to be associated with hot electron recombination and it is speculated that it originates in p-channels in the well adjacent to the AlGaAs cladding. The study provides a technique which can be used as a tool to determine the quality of GaAs quantum wells.

Using high-resolution electron energy-loss spectroscopy (HREELS) in combination with low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) we have observed drastic differences in the uptake of atomic hydrogen at clean InP(100). -surfaces before and after ion bombardment. The initial uptake of atomic hydrogen at well-ordered InP(100) 4x2-urfaces occurs in essence by the Insurface atoms this indicates an Inrich surface. With higher exposure to atomic hydrogen an increase in the phosphorous signal relative to that of the indium hydride is observed. Simultaneously the low-energy electron-diffraction (LEED) pattern is changed from a 4x2 structure for the clean surface to 4x1 and finally to lxi. Substrate surface bonds are disrupted and this favours the formation of phosphorous hydrides. XPS shows no significant changes in the P 2p/In 3d intensity ratio in the examined exposure range. In particular isochronal annealing experiments indicate that phosphorous hydrides are more stable than indium hydrides. Furthermore both hydrides are more stable in the advanced than in the initial stages of hydrogen interaction. For the ion-bombarded surface the P-H/In-H intensity ratio increases by a factor of five if compared to the value obtained at the annealed 4x2-surface. This ratio can be increased further by extending the sputtering time. The latter data indicate predominantly broken P-bonds and the formation of Inclusters.

Luminescense and photoconductivity measurements were performed on MBE grown ZnSe layers with various arsenic concentrations. Two shallow acceptor levels with energies of 125 meV and 260 meV were found. Increasing the As content in order to increase the number of shallow acceptor states resulted in highly compensated samples. For Li the acceptor binding energy was found to be 113 meV. Also in the case of Li a higher doping concentration did not augment the shallow levels. Electrical characterization of the Li doped samples was done by C-V and I-V measurements. The films were found to be p-type.

The initial stages of the growth of CdTe on (100) GaAs with 14. 7 lattice mismatch has been simulated. It is shown that growth in (111) direction with the presence of twins is always preferred on perfect substrate surfaces. In the case of growth in (100) direction misfit dislocations are formed. The critical thickness is evaluated by extrapolation to be 6 - 8 atomic monolayers .

In this work we will report the growth of ZnSe and ZnS grown by atmospheric pressure MOVPE with a rotating substrate which allows a very good thickness homogeneity of the layers. As reactants diethylzinc dimethyizinc diethylselenide and H2S and as carrier gas H2 was used. High mobilities and low background doping concentrations (i3ooK 370 cm2/Vs n3(JK 7x 1014 cm3) sharp excitonic PL features and very thin (2nm) ZnS/ZnSe multilayer structures demonstrate the facilities of this growth technique.

InAs/InP quantum well (QW) structures are grown on InP substrates by hydride vapor phase epitaxy (HYPE) in a continuous mCi H2 HC1 flow with alternate supply of AsH3 and PH3. Photoluminescence peaks due to InAs QW are clearly detected with the higher energy ever reported (1. 23 eV) and with very good value for the full half width maximum (FHWM up to 1 3 meV). The evolution of the peak emission as a function of thickness leads us to determine a critical thickness of 7-8 ML for the InAs/InP system.

A high energy shift of the band-band recombination has been observed in the PL spectra of the strained InP epilayer on GaAs by MOCVD. The strain determined by PL peak is in good agreement with calculated thermal strain. The surface photovoltalic spectra gives the informations about energy gap lattice mismatching and composition of heteroepilayers diffusion length surface and interface recombination velocity of minority carriers of heteroepitaxy layers.

Epitaxial Lift-Off is a technology where a thin epitaxial film is removed from its substrate an grafted to another substrate. The problems encountered during this process will be described and an overview will be given of the devices and integrated circuits realised with this technique.

The changes in the chemical and optical properties of the thin (8001200 A) layers of As2S3 after exposure with photons (1 to 40 J/cm2) electrons (3. 2. 1O to 1. 28 102 C/cm2) or soft Xradiation (0. 1 to 1 1 1 . 0 J/cm2) are studied. The structural changes occurring after exposure lead to changes in the alkaline stability of the exposed regions. The optimum exposure doses for As 25 3 layers are determined allowing their use for ebeam and xray lithographic purposes. The high stability of the layers to a great number of acid etchers used in microelectronic technologies and the stability in TUE conditions in oxygen medium make the layers accomplishing microlithographic tasks.

Near UV excimer ablation of transparent polymers can be improved or even enabled by doping using organic dyes. Polymethylmethacrylate (PMMA) and polystyrene (PS) have been investigated using both photostable and photoreactive dopants. The best results with regard to etch quality and effectivity have been achieved with 1,3- diphenyltriazene, which supports the ablation process by photoeliminating nitrogen. Etch rates of 50 jim/pulse can be reached at 308 nm and 351 nra. The etch rate does not depend entirely on the low level absorption coefficient of the doped polymer.

The heteroepitaxial growth of InP and Ga0471n053 As on GaAs substrates have been investigated by using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) as group V sources. The group III sources are ethyldimethylindium (EDMIn) and triethylgallium (TEGa). The growth process was carried out in a hydrogen flow in a horizontal reactor, where the substrates were placed on a radiatively heated, silicon carbide-coated graphite plate. Heteroepitaxial InP layers with mirror smooth surfaces were deposited on GaAs substrates using a two temperature growth process under atmospheric pressure: a buffer layer was deposited at 400°C followed by the deposition of an epitaxial layer at 500°-550°C. InP layers deposited without intentional doping are n-type with a net electron concentration of (2-3) x 1016 cm3. The FWHM of the excitonic peak of the 4.2 K photoluminescence of an InP layer of 1.1 m thickness is 5.2 meV. Heteroepitaxial Ga0471n053As layers were also deposited on GaAs substrates by the two temperature growth process under reduced pressure using an InP or a Ga0471n053As buffer layer grown at 400°C and the subsequent epitaxial growth at 5OOO 550°C. The composition of the GaInAs layers was determined by x-ray diffraction, photoluminescence, and optical absorption measurements. As-grown surfaces of Ga0471n053As layers of about 2 j&m thickness are visually featureless; however, dislocation density on the order of 108 cm2 was observed by chemical etching and SEM examinations.

We used molecular hydrogen in the presence of a hot tungsten filament to clean GaAs(100) wafers after inserton into an UHV4 chamber. The H2-pressure was varied between lxlO torr and 5x10 torr. During exposure the sample remained either at room temperature or at elevated temperatures up to 600 K. The mechanism we suggest for the removal of oxygen and carbon is the formation of chemical products like H90 and CH4 and their subsequent desorption. Also a build-up of gaflium- and arsenic-hydrides and their desorption is possible. After cleaning a clear ixi-LEED pattern indicates a rather well-ordered surface.

The high performance AuCr/Si02/InSb metal-oxidesemiconductor capacitor was fabricated successfully using photo-enhanced chemical vapor deposition. The 1200 A thick Si02 layer was deposited on the InSb substrate at the temperature below 200 °C. Their electrical and structural properties were analyzed by capacitance-voltage and Auger electron spectroscopy, respectively. The capacitance-voltage results show that the optimal growth temperature of Si02 is 150 °C at which the fiat-band voltage of the capacitor is close to ideal and slow interface state density is less than 5 x 1O'° cm2. For Si02 deposited at lower temperature, although the flatband voltage and interface state are poorer, the subsequent thermal annealing at 150 °C for 12 hours improves both quantities to the level as the optimal condition. However, for Si02 deposited at higher temperature (190 °C), the flatband voltage shifts to -4 V and the slow state density increases to 1.1 x 1011 cm2. It is found from Auger depth profile that whatever the deposition temperature was a Si-rich region followed by an oxygen-rich region was formed at the 5i02/InSb interface. These observations are shown to be consistent with the electrical characteristics of the capacitor.

The physical properties of the PMMA-EVA , a poly (methylmetacrylate) with 7% by wt. of poly (ethylene-covinylacetate) blend,have been investigated with a photoacoustic technique, which allows us to analyse the absorption as a function of the wave length. The informations obtained from the absorption spectra of this blend are useful in interpreting the behaviour of such a novel material subjected to thermal variations. In recent years, polymer and polymeric blends with high order susceptibility have attracted a great deal of attention in nonlinear optics field. We propose a novel polymeric blend for optical investigation, a poly (methylmetacrylate (PMMA) with 7% by wt. of poly (ethylene-co-vinylacetate) (EVA) blend, and present a simple characterization of this material by photoacoustic technique. This blend is polymerized by an unique technique in which the acrylic matrix is polymerized in the presence of dissolved EVA copolymer. The resulting blend is characterized by an intimate dispersion of rubbery droplets (diameter 1 jim) in an acrylic rubbery particles. The PMMA-EVA thermograph in the temperature range - 50 °C to 220 °C exhibits a phase transition at 50 °C, when 10% of EVA melts. Since this polymeric blend suffers an abrupt diffusion near the temperature of the phase transition (- 50 °C), we used the photoacoustic spectroscopy (PAS) in order to compare the absorption spectra at several temperatures. This technique, based on the photoacoustic effect, makes possible the analysis of samples with high absorption and/or scattering.

Based on the coupled wave equation model, this paper presents a theoretical study of the fifth order harmonic generation in organic liquids emphasizing the contribution of the direct and step processes. The elaborated model permits the computer optimisation of the inter acting conditions in order to obtain high conversion efficiencies.

In this study we apply a variational method for the calculation of the dynamic second-order susceptibility tensor. The CNDO approximation, including an extended basis set, is used. Comparison with experimental result is performed for the molecules CO. H20, NH3, (CH3)20 and CH3OH.

Fully processed A1GaAs/GaAs LEDs were lifted off their GaAs substrates and grafted to various host substrates. Due to a metallic back reflector beneath the epitaxial structure, the LED output power was 2 to 3 times increased compared to LEDs still on a GaAs substrate. Output power and spectral responses were significantly influenced by the thermal properties of the host material.

Interdiffusion between epitaxial layers of (Hg,Cd)Te of unequal composition (in the limit, HgTe and CdTe) gives rise to non-abrupt interfaces in heterostructure devices composed of these materials. In this paper, it is proposed that a strained ZnTe barrier layer, interposed at such a heterointerface, may inhibit interdiffusion. Initial results obtained from a CdTe-ZnTe-HgCdTe test structure grown by MOVPE at 325°C are presented. TEM observations and electron microprobe measurements indicate that distinct interfaces are maintained.

Excitation of surface magnetoplasma waves in the CdHg1Te semiconductors has been effected by the method of disturbed total internal reflection following the Otto scheme at the wavelength of 2 mm, in the temperature range 0.3 KT<77 k. The temperature dependence of measured surface characteristics in the semiconductors are discussed as well as their interplay with similar volume ones.

Fabrication of infrared sensor arrays in epitaxial lead-salt layers on Si are described with PbS, PbTe and Pb1SnSe for the SWIR, MWIR and LWIR range. Epitaxy of the 2-3 jim thick layers is obtained with the aid of a 200 nm thick stacked CaF2-BaF2 buffer. Linear arrays with 66 elements were fabricated. For the LWIR range, an array with 10.5 jim cut-off wavelength at 77K and spread below 0. 1 im demonstrates the superior homogeneity achievable with IV-VI materials compared to MCT. The mean quantum efficiency of this array is 59% with 3% standard deviation of the individual sensors.

(100)CdZnTe epilayers are grown by hot wall beam epitaxy (HWBE) on (100) GaAs. The CdZnTe epilayers are used as substrates for the growth of Hg1_CdTe (x = 0.27 - 0.32) layers by closed space vapor phase epitaxy. The Hg1CdTe layers have an x-ray rocking curve width of 59 10 arc sec measured across a 1 inch wafer. The layers are p-type with a hole concentration of 2 - 4.1016crri3 and a mobility of 250 - 350cm2/Vs at 77 K. Photoconductivity decay measurements give the lifetime of excess carriers which is governed by recombination via Shockley-Read centres at T < 250 K. Linear arrays of planar, photovoltaic detectors are fabricated by implantation of B ions. The elements size is 50 50,arn2, the space between the elements is 50prn. The R0A product, the responsivity and the cut-off wavelength of the p-n junction are measured at 192 K. The variation of the responsivity across a 16 element array is less than 4 %, the cut-off wavelength varies between 4.77,um and 4.83μm.

The electrically excited cyclotron resonance (CR) emission is investigated for the 2-dimensional electron gas in AlGaAs/GaAs heterostructures. The effect of sample inhomogeneities and impurities has been investigated by degrading samples by e-beam irradiation and by growing samples with an impurity scattering layer close to the interface. The CR absorption has been studied for comparison. A good correspondance of the two methods has been found: peak shifts are exactly reproduced and Landau level filling factor dependent linewidth oscillations occur in both cases. However, the absolute value and the oscillation amplitude of the linewidth are larger for the emission. This effect is explained by electrical heating and the magnetic field dependent current distribution, and forms a strong limitation for such current driven CR emission sources.

We report on a systematic study of the growth of high quality films of GaAs on Si substrates for co-integration in optical interconnects. The effort was geared towards optimizing substrate preparation, growth time parameters and post-growth treatment for best active layer properties. In particular, the study of growth involved optimization of chemical substrate preparation, study of silicon substrate orientation, ex-situ and in-situ treatment, as well as multi- layer and silicon buffer layers. For quantification of film quality, a number of characterization methods were used both in-situ (RHEED, Auger) and ex-situ (Optical, Electrical (I-V, C-V, DLTS), Hall, ThM, SEM, ECP, XRD). Schottky Diodes, p-n heterojunctions and MSM Photoconductors/ Photodetectors (PC/PD's) were fabricated on these films. A comprehensive study was performed on the PC/PD's, chosen as the test optoelectronic device, for maximum photosensitivity and minimum leakage current. The results allow us to claim that we have achieved a technology that leads to heteroepitaxial GaAs/Si films which compare to homoepitaxial GaAs/GaAs within about 10% in performance in most areas relevant to optoeleclxonic devices. In addition, a reduction of a processing temperature by 100°C was achieved.

The present study reports new research results of a dislocation structure of single crystalline SiC layers grown by CVD on Sisubstrates without a buffer layer. Connection between variation in dislocation 'structure and the conditions of growing has been studied by method of X-ray differential diffractometry. It is demonstrated, the best quality layers, produced at 1100°C and low flow rate of reagent gases, have a block structure, block sizes being approximately 500A.

STRACT Resonant tunneling in threedimensionally quantum confined (3DQC) microcrystalline silicon surrounded by amorphousSi02(aSiO barriers is experimentally observed. Unlike quantum confinement in lower dimenstons charge accumulation in 3DQC silicon box results in large shifts of the discrete energy states with conductancegate voltage measurements.

The development Il-VI semiconductors for the preparation of devices, when compared with Si and the III-Vs, has been much slower and has been restricted by a number of factors. One of the more important of these, at least until the mideighties has been the lack of suitable low temperature epitaxial growth technologies. The main problems that are being addressed in order to hasten the development of Il-Vis concern firstly the need to improve crystalline quality by growth at reduced temperatures(1) and secondly, in the case of the wide band gap Il-Vis, the need to achieve both p and n-type doping that is suitable for device applications. Advances in the last few years in MOVPE, MBE(2) and related epitaxial techniques such as MOMBE, CBE and ALE-MOVPE now offer scope for overcoming these problems. With the exception of MBE these technologies rely on the use of organometallic precursors and these materials are playing an increasingly important role in the evolution and development of the Il-Vis. They represent the key to the future. The purpose of this paper is to review and rationalise the status of current developments in precursor research and then to consider whether these developments are appropriate to solving the problems that are now evident.

Since the last few years there is an increasing interest for materials dealing with nonlinear optical effects. Besides semiconductors, crystalls and organic materials specific attention has been paid to silicate glasses in which a CdSSe1 > microcrystalline phase is thermally developed. These glasses are the basis for a commercially available set of yellow-to-red "sharp cut" filters. Although these glasses have not been optimjzd3for nonlinear behaviour by now, they already show large nonlinear effects.

In this paper we will describe recent results obtained with the shadow masked growth (SMG) technique. This technique enables us to change the growth velocity over the substrate by changing the window dimensions in an epitaxial shadow mask. The influence of the distance between the mask and the substrate and the undercutting of the mask has been studied. First results on optoelectronic devices realized with the SMG technique will be described. These include LEDs, laser diodes and an extended cavity laser diode.

Using Deep Level Transient Spectroscopy (DLTS), we have studied a GaAs/GaInAs/GaAs single quantum well. The DLTS spectra exhibit both a peak and a plateau : the peak is associated with the thermionic emission of electrons and the plateau (ranging from 4 to 30 K) corresponds to a quasi constant emission rate associated with a tunneling emission of electrons from the well towards the conduction band. Varying the polarization applied to the sample during the DLTS measurements, it is possible to observe only one phenomenon : thermionic or tunneling emission. A modelisation of the tunneling effect is proposed, based on Oppenheimer's approach as to the WKB approximation. Finally, the experimental results are discussed.