We have fabricated and measured detailed bit error rate experiments on a 12 channel parallel optical interconnect transmitter operating at 1 Gb/s per channel, using InGaAsP/InP (lambda) equalsQ 1.3 micrometers lasers. The lasers are highly uniform, the channel crosstalk is less than 1 dB, and the mode selective losses are low (< 1 dB). This transmitter has been demonstrated in an architecture which would allow the transmission of 120 channels of 100 Mb/s uncompressed video signals. We have also demonstrated a novel high speed high quantum efficiency CMOS compatible Si MSM detector which would be ideal for monolithically integrated receiver arrays.

Conventional nanosynthesis involves film growth followed by direct-write nanolithography. The last step has two major shortcomings in that (a) it causes material damage to the nanostructures and (b) it is always serial in nature whereby each wafer has to be patterned one at a time. The latter makes it impractical for large-scale commercial applications. To overcome these drawbacks, we have developed a novel and `gentle' electrochemical process for fabricating quantum dot arrays that allows parallel processing of millions of wafers. It causes minimal damage, is much cheaper than conventional nanolithography, and yet has the spatial resolution (approximately 1 nm) of state-of-the-art techniques. Semiconductor quantum dot arrays produced by this process show strong signatures of quantum confinement in their photoluminescence spectra. Superconducting quantum dots show a significant transition- temperature shift arising from an interplay of superconductivity with quantum confinement, while ferromagnetic quantum dots give rise to a novel giant magnetoresistance effect caused by remote spin-dependent scattering of electrons. These structures have also been characterized by a variety of analytical techniques--all of which attest to their high quality.

For the first time, monolithic optoelectronic receivers for a wavelength of 1.3 micrometers have been fabricated successfully on GaAs substrates using InGaAs metal-semiconductor-metal (MSM) photodiodes and AlGaAs/GaAs/AlGaAs high-electron-mobility transistors (HEMTs). Using molecular beam epitaxy (MBE), the photodetector layers were grown on top of a double (delta) -doped AlGaAs/GaAs/AlGaAs HEMT structure which allows the fabrication of enhancement and depletion field effect transistors. The photoabsorbing InGaAs layer was grown at 500 degree(s)C. To fabricate the optoelectronic receivers, first, an etch process using a combination of non-selective wet etching and selective reactive ion etching was applied to produce mesas for the photoconductors and to uncover the HEMT structure in all other areas. For the electronic circuits, our well-established HEMT process for 0.3-micrometers transistor gates was used which includes electron-beam lithography for gate definition and optical lithography for NiCr thin films resistors, capacitors, and inductors. The interdigitated MSM photodiode fingers were also fabricated using electron-beam lithography. For interconnecting the electronic circuits and the photodetectors, air bridges were employed. The entire process was performed on 2-inch wafers with more than 90% yield of functional receivers. The finished receiver--basically an MSM photodetector linked to a transimpedance amplifier--is operational at an incident wavelength of 1.3 micrometers at data rates up to 1.2 Gbit/s. The sensitivity of the detectors is 0.16 A/W at a 10 V bias.

The collapse of the Soviet Union opened many areas of laser technology to the West. E-beam- pumped semiconductor lasers (EBSL) were pursued for 25 years in several Soviet Institutes. Thin single crystal screens of II-VI alloys (Zn_xCd_1-xSe, CdS_xSe_1-x) were incorporated in laser CRTs to produce scanned visible laser beams at average powers greater than 10 W. Resolutions of 2500 lines were demonstrated. MDA-W is conducting a program for ARPA/ESTO to assess EBSL technology for high brightness, high resolution RGB laser projection application. Transfer of II-VI crystal growth and screen processing technology is underway, and initial results will be reported. Various techniques (cathodoluminescence, one- and two-photon laser pumping, etc.) have been used to assess material quality and screen processing damage. High voltage (75 kV) video electronics were procured in the U.S. to operate test EBSL tubes. Laser performance was documented as a function of screen temperature, beam voltage and current. The beam divergence, spectrum, efficiency and other characteristics of the laser output are being measured. An evaluation of the effect of laser operating conditions upon the degradation rate is being carried out by a design-of-experiments method. An initial assessment of the projected image quality will be performed.

A normal incidence tapered laser amplifier is shown to produce more than 4.5 W optical power at 810 nm in a diffraction-limited beam. A new angled-facet tapered laser amplifier has demonstrated as much as 5 W optical power in a diffraction-limited beam at 810 nm with only a few mWs of coupled input power. Angled-facet laser amplifiers exhibit near-ideal Gaussian beam characteristics. More than 1.9 W CW is obtained in a 970 nm angled-facet tapered laser amplifier. A near-ideal beam quality factor M² is obtained.

In this paper we report the observation of spikes in the intensity power spectra of strained- layer multiple quantum well lasers emitting at wavelengths of 1.3 micrometers and 1.5 micrometers . The spacing between the spikes on fiber-pigtailed lasers was equal to the mode spacing of the fiber resonator (Delta) (nu) _fiber equals c/(2 N_gL) where c is the speed of light, N_g is the group index, and L is the length of the fiber.

We propose a new accurate method for differential carrier lifetime measurement, in which the laser under test biased below threshold is optically modulated. Experimental results are very reproducible and show very high signal/noise ratio. No additional technological process for the laser under test are required.

Visible laser diodes (LD), based on AlGaInP/GaInP/GaAs material system, are of great interest, because of large scale application in the information reading and aiming. Heterostructures for such a type of LD were grown successfully by MOCVD. As mentioned by most authors the main problem, which has place during the growth technology developments, is low value of temperature threshold coefficient T₀. This problem is due to low conductive band discontinuity and p-doping efficiency. Holes concentration in p- cladding layer determine T₀ coefficient significantly, preventing leakage currents from active layer. Further it has been found, that hydrogen can passivate zinc atoms, incorporated into AlGaInP quaternary alloys. Comparing with AlGaAs/GaAs material system several new parameters should be controlled during AlGaInP layers growth: extent of ordering and growth rate. So, new degrees of freedom appears during growth and significantly affect growing results, epilayer parameters and, consequently, quality of manufactured laser diodes. This work is directed to show, how such growth parameters like: growth rate, growth temperature, and DMZn gas phase concentration; determine heterostructure quality.

Recent femtosecond time-resolved pump-probe experiments have detected large amplitude oscillations due to coherent phonon generation in the reflection (R) from various materials). These oscillations show only vibrational modes with A₁ symmetry, even though other Raman-active modes of comparable Raman cross section exist. Experimental results showing the properties of this phenomena and a model that explains many of the experimental phenomena are presented.

This paper reviews some recent developments in the use of the contactless, and hence nondestructive, electromodulation methods of photoreflectance and contactless electroreflectance for the room temperature characterization and qualification of semiconductor device structures. These include heterojunction bipolar transistors, pseudomorphic high electron mobility transistors, depletion and enhancement mode transistors, quantum well lasers, vertical cavity surface emitting lasers, multiple quantum well infrared detectors and solar cells.

The principle of spin tracing is based on the exchange interaction between charge carriers and magnetic ions, which is known to produce giant magneto optical effects in Semimagnetic- or Diluted Magnetic Semiconductors. The idea of spin tracing is exploited in the Zeeman method of interface characterization to study spatial distribution of magnetic ions interacting with a carrier (exciton) confined in quantum structures made of ternary CdMnTe compounds. In this paper we give a concise description of the spin tracing method followed by a review of available experimental data related to the influence of interfaces on the Zeeman effect in structures with barriers containing magnetic ions. A critical review of strong and weak points of the method is given accompanied by a discussion of its practical applicability. Special attention is paid to studies of annealing processes of low dimensional structures using the Zeeman method. We analyze the results obtained so far on quantum wells and superlattices and discuss perspectives of further studies.

Ellipsometric spectra of insulating and conducting polyaniline films have been measured in the wave-length range of 300 nm - 800 nm. The dielectric function and the refractive index of various polyaniline films have been determined. Two absorption bands of the insulating polyaniline correspond to the interband transition and the exciton transition. More band structures in the spectrum of conducting polyaniline have been discussed and identified to the polaron transitions. The values of refractive index are between 1.31 and 1.64 for the insulating films, and between 1.37 and 1.57 for the high-conducting films. The nonlinear optical coefficient has been determined by the time-resolved absorption saturation measurement and the Z-scan measurement. The value of third order nonlinear susceptibility up to 3 X 10^-10 esu at 630 nm has been obtained. The dimensionality and the dimension crossover of these low-dimensional solids have also been studied.

The use of scanning probe microscopies--such as Scanning Tunneling Microscopy (STM) and Ballistic Electron Emission Microscopy (BEEM) to study carrier transport through semiconductor heterostructures--is reviewed. The ability of BEEM to probe buried structures below the surface can be exploited to study heterostructure band-offsets and resonant tunneling through quantum structures. It will be shown that BEEM can serve as a powerful probe of the spectroscopy of such structures. The implications of such studies for research on quantum dots and the characterization of new optoelectronic materials will be discussed.

Exciton and biexciton binding energies, and wave functions are calculated with a three parameter variational model in an effective mass approximation for a rectangular GaAs quantum well wire surrounded by an AlGaAs cladding. Moreover, the Al interdiffusion into the wire and the finite band offsets between the wire and the cladding have been included. The Coulomb interaction terms are treated exactly in their full 3D form throughout the calculation, especially in the case of the biexciton, a more physically realistic procedure then used in previous calculations which employed an effective 1D potential. Our treatment is unique in the use of a 2D Fourier expansion in the Coulomb potential terms. For the range of dimensions studied, the inclusion of the Al interdiffusion had a pronounced affect on the binding energies when compared to those obtained from the infinite barrier model. Using the results of the exciton and biexciton calculation, we calculate the third-order nonlinear optical susceptibility as a function of pump-probe frequencies in a small range about the exciton absorption resonance. We have found, depending upon wire dimensions and the amount of pump detuning, values of the susceptibilities to be on the order of 10^-1 esu and a large off-resonance optical gain due to biexciton formation.

A new optical instrument allowing photoellipsometric measurements is presented. Photoellipsometry (PE) is a modulation spectroscopy technique which uses ellipsometry in presence of a chopped external light excitation. PE measurements are obtained using a double modulation system, combining spectroscopic phase-modulated ellipsometry (SPME) with a laser pump beam. The experimental system described here takes advantage of the high frequency polarization of SPME (approximately equals 50 kHz). As a consequence the frequency of the pump beam can be varied up to 5 kHz. The field-induced changes in the real and imaginary parts of the bulk dielectric function can be directly measured and analyzed in terms of the pump beam power or the probe beam photon energy. Demonstration of this method is made with measurements, recorded in the band-gap E₀ region (approximately equals 1.4 eV), on n-type GaAs sample. In particular, Franz-Keldish oscillations are observed with a very good sensitivity. More generally, PE measurements are compared with a theoretical model. From this preliminary study, it can be concluded that PE appears as a promising technique for semiconductor characterization.

Experimental set-up has been established by using high resolution monochromator as well as He-Ne and Ar multiline lasers. Epitaxial, undoped and doped (Si and Zn) GaAs and GaAlAs layers as well as heterostructures of GaAs/GaAlAs have been grown in atmospheric pressure vertical MOCVD system. Room temperature photoreflectance (PR) have been applied to characterize layers, heterostructures as well as the multiple quantum wells. The surface and interface related PR have been studied by means of Kramers-Kronig analysis. Decomposition of PR spectrum into the spectra connected with surface region and with the interface has been proposed. Modulus of the complex photoreflectance gives us the critical point energy, whereas the phase of this function can be used for a carrier concentration topography.

First observation of electroluminescence in type II broken-gap p-GaInAsSb/p-InAs single heterojunctions is reported. Intensive spontaneous emission was obtained under applied bias at T equals 77 - 300 K. Two narrow `resonant' emission bands were observed in the spectral range 3 - 5 micrometers at T equals 77 K with full width at half maximum about 1 - 2 kT. It was established that effect of unusual electroluminescence in isotype type II broken-gap p-p- heterostructure due to indirect (tunnel) radiative recombination of spatial separated 2D- electrons and holes localized in deep adjacent quantum wells at different sides of the interface. Novel tuneable mid-infrared light sources are proposed.

Infrared sensors are generally considered a specialized product for military applications. With the reduction in the projected volume to be procured by the military, industry is actively pursuing new applications of IR sensors in security, surveillance, medical, and process control systems. With this expansion of the potential application base, rapid response to customer requirements and further cost reductions are essential to respond to the future marketplace. Initiatives to develop new detector and JR sensor technologies must maintain this new market perspective. This paper reviews market potential and describes technology initiatives necessary to produce a wide variety of JR sensors in low volume and at affordable cost. The initiatives address all aspects of the JR sensor module production, including the detector, packaging, cryogenics, and electronics. Since the sensor design is an integral part of the overall electro-optical system design, software tools linking sensor specifications to system requirements are also essential to the production of affordable sensors in small quantities. Utilization of this integrated sensor/system design trade space early in the design process provides the capability to make cost/performance tradeoffs that are useful in guiding the selection of detector configuration, packaging, and electronics. Integration of these design activities with factory process capabilities provides the potential for rapid production of new sensor designs at an affordable cost, even in low volume.

The ultimate signal-to-noise performance of the semiconductor photodetector is limited by the statistical fluctuations of the thermal generation and recombination rates in photodetector material. Cooling is an effective but impractical way of suppression of the thermal processes. The performance of uncooled detectors can be improved by minimizing the thermal generation and recombination rates and reducing the actual volume of photodetector. This can be realized in 3D heterostructure devices. In these devices, the incident radiation is absorbed in small regions of narrow gap semiconductor, buried in wide gap volume and supplied with wide gap electric contacts and radiation concentrators. The practical near room-temperature 1 - 12 micrometers IR heterostructure photodetectors are reported. The devices are based on variable gap Hg_1-xCd_xTe. The 3D heterostructures have been obtained by Isothermal Vapor Growth Epitaxy in a reusable growth system which enables in situ doping during growth with foreign impurities. Ion milling was extensively used in preparation of the devices. Monolithic optical immersion has been applied for further improvement of performance. The 3D heterostructure devices exhibit performance exceeding that of conventional photodetectors.

Quantum well and superlattice IR detectors have recently become visible contenders for many military applications. In this paper we present an overview of the issues related to quantum well and superlattice IR detectors and discuss in detail, the issues related to the application of these detectors for space missions.

Astronomical instruments for the study of UV astronomy have been developed for NASA missions such as the Hubble Space Telescope. The systems that are `blind to the visible' (`solar-blind') yet sensitive to the UV that have been flown in satellites have detective efficiencies of about 10 to 20%, although typically electron bombardment charge coupled devices are higher at 30 - 40% and ordinary CCDs achieve 1 - 5%. Therefore, there is a large payoff still to be gained by further improvements in the performance of solar blind UV detectors. We provide a brief review of some aspects of UV astronomy, UV detector development, and possible technologies for the future. We suggest that a particularly promising future technology is one based on the ability of investigators to produce high quality films made of wide bandgap III-V semiconductors.

With the advancement of high bit rate optical communication system, there is a need for a high speed photo detector. Results have been presented for a n⁺-n^-- n⁺ small geometry GaAs diode under optical illumination. The potential at the n⁺-nl-interface is found to be more negative due to the photovoltaic effect. The current increases with the increase in absorption coefficient and radiation flux density. The quantum efficiency is over 70% in the wavelength spectrum 0.6 - 0.8 um being more than 80% at 0.76 um. The device can be used in GaAs material for 1.55 um system.

There are many applications where incoherent laser diode arrays are useful if high brightness can be maintained. The light emitted from the facet in high power individual devices is approximately 5 MW/cm2/steradian, but methods are needed to maintain this brightness when a number of devices are combined. The typical output is asymmetric in beam divergence and in source size. Several approaches are being evaluated at NVESD to combine linear and 2D arrays and produce a beam divergence of a few milliradians with a nearly symmetrical output. The approaches being explored include turning mirrors, combinations of refractive and diffractive optics, and novel heat sink packages. In preliminary experiments, micro-optics and diffractive optical elements have been used to colliminate the output from a 20 watt CW linear array and produce a 4 X 6 milliradian beam. Brightnesses of more than 1 MW/cm²/steradian are projected with improved components.

The development of complex optoelectronic devices and circuitry, including optoelectronic integrated circuits, vertical cavity surface emitting laser arrays, and light emitting diode (LED) arrays, may be simplified by the separation of the circuitry and epitaxial layers from the substrate. This separation permits access to the back side of the epitaxial film, allowing back side metallization for interconnects and mirrors, as well as improved heat sink attachment. We describe the results of the successful fabrication of 2D arrays comprising 32,768 monolithic LEDs. The individual LEDs are addressed through a multiplexing circuit in which row addressing is provided on the front side of the epitaxy, and column addressing is provided on the back side. The monolithic LED array is dense, consisting of center to center device spacing of 50 micrometers . The epitaxial films were formed by conventional metal organic chemical vapor deposition, with AlGaAs active layers emitting at 650 nm. A separation layer of AlAs is used to facilitate substrate removal. The fabrication process and results will be described.

The aim of this work is to present the main optoelectronic characteristics of large area 1D position sensitive detectors based on amorphous silicon p-i-n diodes. From that, the device resolution, response time and detectivity are derived and discussed concerning the field of applications of the 1D thin film position sensitive detectors.

Indium tin oxide (ITO) thin films would be highly useful as ohmic contacts for a wide range of optoelectronic applications because they provide low resistance and are optically transparent. We have investigated in particular the ITO/InP system for application to homoepitaxial InP solar cell. We have deposited ITO by excimer laser ablation in low temperature (250 degree(s)C) without any additional processing. Results have been highly encouraging: transmission properties are comparable to those obtained with other technics and measurements on solar cells indicate that the electrical properties are also satisfactory, a conversion efficiency of > 13% have been obtained with unoptimized contacts and no antireflection coating. Hall measurements have given carriers concentration and mobility, and Auger profilometry has revealed an abrupt interface, negligible interdiffusion of P and O, opening the way to excellent ITO contacts to epitaxial devices made from InP and possibly other materials.

The refractory or wide bandgap semiconductors are replacing gallium arsenide (GaAs) as the semiconductor of the future and they are doing it now. These semiconductors exhibit many unusual properties that are just now being exploited. Their exploitation is expected to engender many new device and electromagnetic systems concepts. Already transistors of these materials have exhibited the highest power densities of any RF transistor, transistor operation to 80 GHz, the first and the most efficient blue light emitting diodes, and negative electron affinity properties rendering them with ideal properties as cold cathodes. Among the most recently discovered of these properties is that of electron transport at energy levels (velocities) orders of magnitude greater than their bandgaps and--unlike conventional semiconductors--are seemingly not heavily scattered by optical phonons. This property is expected to lead not only to much higher frequency devices but to a new class of optical emitters as well.

We describe the deposition and characterization of single layers, homo-heterojunctions and superlattices of the Al_xGa_1-xN and In_xGa_1-xN material systems. Measurements are discussed indicating of 2D electron gas at heterojunction interfaces. Several photonic devices such as UV detectors, quarter wave reflector stacks, light emitting diodes and optically pumped lasing cavities are also described.

We describe optoelectronic effects in GaN/AlGaN Heterostructure Field Effect Transistors (HFETs) and Heterostructure Insulated Gate Field Effect Transistors (HIGFETs). GaN/AlGaN HFETs operate as visible blind photodetectors with responsivities as high as several thousand A/W for wavelengths from 200 to 365 nanometers. GaN/AlGaN HIGFETs exhibit light- sensitive long term current-voltage characteristic collapse after an application of a high drain- to-source bias. This collapse is removed by illumination with light with certain wavelengths. We suggest that this collapse is a consequence of hot electron trapping in the AlN barrier layer near the drain edge of the gate.

Robust second-order optical nonlinearities comparable to those in common nonlinear optical materials have been reported in metal nitrides. In this paper we present experimental studies of gallium nitride and aluminum nitride thin films, including fabrication and optical characterization. The ease of thin film deposition techniques employed for these materials indicate that they may have potential for cost effective development of nonlinear optical waveguide devices.

High quality AlN and GaN epilayers have been grown on basal plane sapphire by low pressure metalorganic chemical vapor deposition. The X-ray rocking curve linewidth of the AlN and GaN films were about 100 and 30 arcsecs respectively. Sharp absorption edges were determined at 6.1 and 3.4 eV respectively. Successful donor-bound excitonic luminescence emissions were detected for GaN films grown on sapphire and silicon. Two additional lines at 3.37 and 3.31 eV were observed on GaN on sapphire and assumed to be impurity-related. Doping of GaN layers was achieved with magnesium. Mg-related photoluminescence emissions were successfully detected on as-grown samples, without any post-growth treatment.

Emerging technologies such as spectroscopic gas sensing can benefit greatly by the development of robust, high-power semiconductor lasers emitting in the mid-infrared spectrum. Great progress has been made with these lasers, especially at wavelengths shorter than about 3 micrometers . Lasers with wavelengths longer than about 3 micrometers , however, suffer from nonradiative recombination mechanisms. As such, they continue to operate with modest power levels at temperatures below 150 K. Practical systems, however, demand higher- temperature operation, preferably above 250 K. The challenge, then, is to suppress the nonradiative recombination mechanisms while enhancing light emission of these narrow- bandgap materials. This paper outlines the progress made to date, including material-growth advances and device-structure designs which have enabled significant advances in the technology. The obstacles to higher-temperature operation, such as Auger recombination, will be identified. The tools being used to overcome these obstacles will also be discussed, including band-structure engineering. Finally, future research in this fertile area will be suggested which could augment current efforts.

We review state-of-the-art aluminum-free GaInP-GaInAsP-GaInAs laser diodes which emit at the wavelength of 980 nm. These lasers are intended for pumping light into erbium-doped optical fiber amplifiers. We discuss the preparing of the layer structure, using the gas-source molecular beam epitaxy growth method, the lasing characteristics, fiber coupling efficiency, and reliability issues.

Recent advances in the development of high purity starting materials and OMVPE reactor design are quickly making OMVPE technology the technique of choice for the manufacturing of epitaxial material needed for optoelectronic devices. Within the past year, at the Jet Propulsion Laboratory we have used a single state-of-the-art AIXTRON 200/4 OMVPE reactor to produce high quality optoelectronic devices from three different material systems; InGaAsP/InP, AlInAs/InAs and AlGaAs/GaAs. Within the InGaAsP/InP family of materials we have been able to develop a regrowth protocol to preserve first order DFB gratings, with a grating depth of 400 degree(s)a. In addition, we have been able to fabricate InGaAs(P)/InP heterostructures with near monolayer abruptness. However, most important, we have been able to develop a dual flow adjustment scheme that results in lattice matched and wavelength matched InGaAsP layers within six to seven iterations of the growth parameters.

Recent progress at Deacon Research in fabricating periodic domain structures in bulk lithium niobate using E-field poling will be presented. Periodic structures have been fabricated for converting the frequency ofnear infrared diode lasers to the visible and mid-JR regions ofthe spectrum using quasi-phase matching. The prospects for fabricating commercially viable integrated optical devices will be discussed. Keywords: quasi-phase matching, frequency doubling, frequency mixing, optical parametric oscillation

We present the results of an experimental study of tunneling in Asymmetric Double Quantum Well (ADQW) structures for which holes were found to tunnel from the narrow well to the wide well on sub-picosecond time-scales. These times are as fast, or faster than electron tunneling times despite the absence of resonances between hole states. Valence band structure calculations for our ADQW structures indicate that ultrafast hole tunneling can be attributed spin-dependent delocalization of the hole wavefunctions with a concomitant singularity (in principle) in the density of final wide well states.

High quality InSb has been grown by Molecular Beam Epitaxy and optimized using Reflection High Energy Electron Diffraction. A 4.8 micrometers InSb layer grown on GaAs at a growth temperature of 395 degree(s)C and a III/V incorporation ratio of 1:1.2 had an X-ray rocking curve FWHM of 158 arcsec and a Hall mobility of 92300 cm²V^-1s^-1 at 77 K, the best reported to date for InSb nucleated directly onto GaAs. InSb p-i-n structures of 5.8 micrometers grown under the same conditions demonstrated a X-ray Full Width at Half Maximum of 101 arcsec and 131 arcsec for GaAs and Si substrates, respectively, and exhibited excellent uniformity of +/- 3 arcsec over a 3' substrate. Prototype InSb p-i-n detectors on Si have been fabricated and have demonstrated photovoltaic response at 6.5 micrometers up to 200 K. These p-i-n detectors have also exhibited the highest D* for a device grown onto Si.

For developing the applications of integrated optics to microwave and millimeter wave systems, a key point is the very high speed modulation of the lightwave. As external modulations seem to constitute the best solution, they need the availability of specific driving devices. The main requirements of these devices are given, in terms of speed (current gain cut-off frequency), current density, and breakdown voltage. The principle and capabilities of various kinds of field effects transistors available are summarized, with a large insistance on those that present the greatest potential such as the High Electron Mobility Transistors (HEMT) on InP substrate. Finally, the recent improvement of performance (speed, current density, breakdown voltage) are presented and discussed. It appears that the requirement on breakdown voltage remains the most difficult to satisfy for very high speed devices such as HEMT on InP but recent results lets hope the availability of satisfying devices in near future.

For systems applications using both optics and microwave, specially designed optoelectronic devices and integrated circuits are often required. Starting from some system applications, we discuss the main performance of opto-microwave devices and show how to design and fabricate them. Particular emphasis is made on new optoelectronic integrated circuits that we call Microwave Optoelectronic Monolithic Integrated Circuits (MOMIC's). Examples of MOMIC's presented here are: matching emitters and receivers, optical circuits made with dielectric materials, multielectrode lasers, millimeter wave transducers.

Erbium-doped glasses are of great interest for optical fiber telecommunications at 1.5 micrometers . The sol-gel process offers many advantages for synthesizing materials for integrated optical devices. Some of these advantages include high-purity, low-temperature synthesis, and excellent control and flexibility over composition and design. In this paper, we report the first Er-doped sol-gel waveguides. We examined several approaches for alleviating the OH^- quenching problem associated with conventional sol-gel processes. We prepared the first ion exchangeable Er-doped glasses which can be fabricated into integrated optical devices. The concept of molecular docking of Er as a coordinate complex in gel matrices to improve the luminescence properties has been applied. We also exploited the concept of using the evanescence field to couple energy into an Er-doped sol-gel layer on top of a glass optical device. New progresses in modifying the properties of gel matrices for integrated optical device applications are presented.

In this paper, recent results on the use of low-energy ions in molecular beam epitaxy are described. Mechanisms for ion damage formation are discussed and conditions where ion irradiation can be used without introducing damage are reported. Three main applications are discussed. First, the use of ions to suppress 3D island nucleation during the early stages of strained-layer growth is presented, with particular attention paid to the ion-induced prevention of extended defect formation and strain relaxation. The current understanding of the mechanisms by which ion irradiation affects nucleation is also summarized. Second, ion- induced suppression of phase separation in InGaAsSb alloys during growth on lattice-matched to InP substrates is described. Third, the application of very-low-energy (approximately equals 50 eV) and glancing-angle 1 keV Ar ions to damage-free sputter cleaning and etching of GaAs is discussed.

Acceptor doped Quantum Well Intersubband Photodetectors with GaAs wells and lattice matched barriers of both ternary (In_0.49Ga_0.51P) and quaternary (In_0.62Ga_0.38As_0.22P_0.78) materials have been grown on semi-insulating GaAs substrates by Low Pressure Metal Organic Chemical Vapor Deposition. Mesa devices were fabricated and subjected to a series of tests to illuminate experimentally some of the detection capabilities of the lattice matched quaternary In_xGa_1-xAs_yP_1-y system with (0 <EQ x <EQ 0.52) and (0 <EQ y <EQ 1). The observed photoresponse cut-off wavelengths are in good agreement with the activation energies observed in the temperature dependence of the dark currents. Kronig-Penney calculations were used to model the intersubband transition energies.

Well-barrier (W-B) hole burning in quantum well lasers is argued to be a consequence of the carrier build up in the barrier during the capture and release of carriers by the quantum well. The rate in this process are characterized by a capture time ((tau) c) and by the in/out ratio ((eta) ) defined as the ratio of the capture and release times for carriers into and out of the well region. In this paper a circuit model to represent W-B hole burning that is responsible for a large change in the threshold current density have been developed from the ratio equations. The model is simulated using the circuit simulation program SPICE for various values of (eta) and compared for a QW with and without W-B barrier hole burning.

The frequency dependence of the various parameters which determines the feasibility of intersubband lasers based on quantum wells are discussed and the more desirable frequency range in terms of each parameter is described. These parameters include the optical gain, the confinement factor, the relaxation rate, and the optical losses. The advantages and disadvantages of employing both electrical and optical pumping for creating population inversion for intersubband lasers are also discussed. Then, the potential problems concerning the realization of some of the proposed laser structures based on intersubband transitions in quantum wells are discussed and the more promising schemes are determined. Based on the recently published experimental results on resonant tunneling processes in coupled quantum wells as well as the free carrier absorption in doped layers, it is concluded that the realization of proposed electrically pumped lasers at far-infrared frequencies is extremely difficult at the present time. This is due to the high free carrier absorption in the doped layers and the inability to invert the population of the upper and lower subbands (laser states) of the quantum well in the active layer. Optically pumped structures do not necessary rely on the resonant tunneling process for creating population inversion and also doped injector/collector layers may be avoided in these structures and hence they could be more promising for the realization of intersubband lasers at far-infrared frequencies.

The optical characteristics and the recombination dynamics of Er-doped Si/SiO₂ planar microcavities are reviewed. We show that the emission characteristics of the optically excited Er³⁺ ions are significantly changed by microcavity effects. For emission-resonant microcavities, the intensity, spectral characteristics, far-field distribution, and spontaneous lifetime are changed. For absorption-resonant microcavities, the absorption efficiency of the 980 nm excitation is strongly enhanced. The results demonstrate that the employment of microcavities in optical as well as optoelectronic devices provides new possibilities to enhance the properties of photonic and optoelectronic devices.

Over the last decade considerable advances have been made in the area of semiconductor lasers as a result of tailoring the electronic structure of the active medium. This has been accomplished through the use of quantum confinement and built-in strain. There has been less emphasis on altering the photonic properties to improve laser performance. In this paper we examine the potential of a surface-emitting microcavity structure with submicron lateral dimensions for improving laser performance. We find that as the lateral dimensions are decreased, the photon density of states starts to change. In particular, strongly resonant states associated with Bragg reflection begin to dominate the photon spectrum. By placing the resonance peak close to the gain peak in the active quantum well region, a number of laser properties can be altered. The dimensions at which the changes start to be significant is about (lambda) /n_a, where n_a is the refractive index of the active region. A study of how the threshold current, dynamic characteristics and laser linewidth change as a function of the microcavity dimensions is presented. Our studies show that the spontaneous emission factor (beta) approaches a value of approximately equals 0.5 for small structures with high mirror reflectivities. This in turn results in essentially zero threshold lasing for a microcavity with lateral dimensions < 0.3 micrometers (for emission at 1.3 eV). The laser linewidth increases as (beta) decreases, but the increase is not proportional to (beta) , and even for small structures, the linewidth is expected to be in the range of 100 MHz to 1 GHz, which may be adequate for many applications. The -3 dB response of the 0.3 micrometers laser exceeds 40 GHz.

Metal-semiconductor-metal photodetectors have been fabricated on undoped epitaxial GaAs material with gold and indium-tin-oxide interdigitated contacts. In both cases, various electrode configurations were laid out with combinations of finger spacings and finger widths ranging from 1 to 3 micrometers and detector cross-sections of 25 X 25, 50 X 50 and 100 X 100 micrometers ². Frequency response measurements were carried out up to 20 GHz using a high-speed electro-optic modulator combined with a DC-operated laser diode and an ultrafast photodetector for system calibration. This frequency domain technique ensures accurate measurement of true analog bandwidth compared to time-domain techniques which can easily lead to an overestimation of photodetector bandwidth. Photodetector responsivity has been plotted as a function of bias voltage. We note that for similar devices, Ti/Pt/Au contact MSMs require lower bias voltages before they reach their saturation bandwidth than ITO contact MSMs. For a 100 X 100 micrometers ² ITO MSM with a 2 micrometers finger width and a 2 micrometers finger spacing, the 3 dB bandwidth was measured to be 4 GHz at 10 V bias. By comparison, similar gold contact MSMs exhibit 3 dB bandwidths in excess of 12 GHz. The difference in speed is partly explained by the higher device parasitics of the ITO MSMs, as confirmed by S₁₁ measurements made on both types of device. The S₁₁ data was also used to extract the MSM equivalent circuit parameters for a high-frequency MSM model. Similar measurements on other electrode configurations show that as expected, the speed of ITO MSMs become considerably higher as device size is decreased, until the limit where transmit-time effects start to dominate the overall performance.

Antiguided arrays (80 micrometers aperture) have demonstrated 0.5 W CW in a diffraction limited beam with reliable operation over several thousand hours. Larger aperture (120 micrometers ) devices have demonstrated 1 W CW in a beam 1.7 X D.L. Due to the parallel nature of the leak-wave coupling, antiguided structures are unique among coupled oscillator systems in that they display temporal stability to high output powers. Preliminary results on aluminum- free InGaP based antiguided structures are 0.5 W pulsed in a D.L. beam from a 40 micron aperture source.

The physical properties of a new high-sensitive photodetector developed on the base of Avalanche heterostructures with Negative Feedback (ANF) are considered. The main difference between such a structure and a conventional avalanche photodiode (APD) is non- stationarity of the electrical field strength in an avalanche region caused by the feedback. It is shown that when the non-stationarity is manifested at amplification of a single photocarrier, it changes radically the main characteristics of the avalanche process. A qualitative physical model of ANF process and the results of numerical simulation and experiments are presented. They exhibit an ability of ANF-based device to provide a unique for solid state photosensor a combination of low noise, high gain and low response time. It is also shown that at the same time the negative feedback enables an avalanche device to be manufactured in multi-element design without serious difficulties. The experimental distribution of gain resulting from single- electron-initiated avalanche events was obtained on a SiC-Si ANF heterostructure, and confirmed the main model predictions. The results, illustrating the process of a few-photon light pulse registration are also presented. The opportunities of ANF-based devices further development are discussed.

A brief review of the main experimental techniques exploiting synchrotron radiation in semiconductor surface and interface physics is attempted. Topics emphasized include the study of surface and interface phenomena, such as structural properties (e.g. surface reconstruction) by x-ray diffraction, interface structural and dynamical properties (e.g. adsorbate vibrational amplitudes) by the x-ray standing wave technique, and the study of heterostructures by a combination of x-ray diffraction, specular reflectivity, etc. This review emphasizes brilliance (the phase-space density of photons) as the main figure of merit for many experimental techniques applicable to research in semiconductor physics. Examples of novel experiments made possible by the so-called `third generation', high-brilliance synchrotron sources are presented.

Bi-Sr-Ca-Cu-O superconducting films consisting of 2223-high T_c single phase have been prepared on LaAlO₃(100) and Nd:YAlO₃(001) substrates without post-annealing by MOCVD. As-deposited films exhibited the highest Tc(zero) of 97 K and the highest Jc of 3.8 X 10⁵ Acm^-2 at 77 K under zero magnetic field as reported so far. It also showed little degradation of Jc under high magnetic field up to 8 T at 77 K. It was speculated through the measurement of the angular dependence of Jc that the origin of such high Jc is primarily attributed to the intrinsic pinning mechanism. AFM observations of these film surfaces have been carried out to elucidate the crystal growth mechanism and the effect of surface structures on superconducting properties. AFM images of the film surfaces grown on LaAlO₃(100) (off angles <EQ 0.3 deg.) and on Nd:YAlO₃(001) (off angle approximately 2.7 deg.) clearly showed a 2D nucleation growth and a step flow growth mechanism, respectively. The magnetic-field dependence of J_c and the observed surface morphologies strongly suggest that these as-grown films have no weak-links, which is a promising characteristic for device applications.

We describe a new and highly precise method for determining the surface coverage during epitaxial deposition of compound semiconductors, using migration enhanced epitaxy (MEE). By monitoring the MEE reflection high energy electron diffraction (RHEED) intensity and a simple simulation of RHEED oscillations, one can determine the surface coverage with an accuracy of much better than 0.01 monolayer per cycle of MEE growth. The simplicity of the method makes it practical and convenient for preparing heterostructures with well defined and well characterized interfaces. The specific results reported are for ZnSe and ZnTe, but the method applies equally well to other compound semiconductors in both the II-VI and the III-V families.

Initial stages of misfit relaxation process in Ge epitaxial films grown by pulsed laser deposition on (001) Si substrates have been investigated by high-resolution transmission electron microscopy. Special emphasis is placed on conditions leading to a 2D (layer-by-layer) growth mode. The evolution of the dislocation network as a function of film thickness and thermal annealing is controlled by surface undulations and interactions between dislocations. The dislocation interactions leading to rearrangements in a nonequilibrium dislocation network driven by elastic interaction between parallel 60 degree(s) dislocation segments are discussed in detail. Based upon our experimental observations, we propose a model for the formation of stacking faults in heterostructures.

We present a new set of experiments in which the attenuation of a `monoenergetic', possibly spin-polarized, free-electron beam is measured by direct transmission through an ultra-thin metal layer. The self-supported metal target is either a reference gold sample or a ferromagnetic structure. The overall thickness is of the order of 25 nm. The magnetic structure consists of a 1 nm-thick cobalt film sandwiched between 21 and 2 nm-thick gold layers, with perpendicular magnetization. Measurements are performed throughout a wide energy range, with incident electron energies between 2 and 1000 eV above the Fermi level. The transmission of the gold layer is found to be substantially higher than that of the magnetic structure. In the latter case, at low energy, close to the clean surface vacuum level, we find that the majority spin electrons are more easily transmitted than the minority spin electrons. Cesium deposition on the exit side or on both sides of the target increases the overall transmitted current by almost an order of magnitude. In the case of the magnetic structure, this also increases the transmission spin-asymmetry from 16 to about 40%. Such structures appear to be well-suited to the construction of convenient and compact spin-detectors.

Ferroelectric oxide thin films have been synthesized by metal-organic chemical vapor deposition for potential applications in OEICs. Initial emphasis has been on the BaTiO₃ system because of its excellent electro-optic and non-linear optical properties. Epitaxial thin films have been prepared with excellent ferroelectric properties. Second-order non-linear susceptibilities of the thin films approaching the bulk value have been measured. The doping of the thin films with the rare earth ion Er has been achieved. Strong characteristic 4f shell emission has been observed at 1.5 micron under optical excitation. This suggests that BaTiO₃ thin films may be well-suited as a gain medium for integrated optical amplifiers. Other ferroelectric epitaxial films have been synthesized including SrBaNb₂O₆ and KNbO₃ and their nonlinear optical properties measured. Prospects and challenges for integration of these ferroelectric thin films in OEICs are discussed.

Data for high-temperature superconductivity are analyzed in order to determine the required nature of a successful general theory of oxide superconductivity. (1) The p-type nature of high-temperature superconductivity requires a model based on oxygen. (2) Since ideal (Rare- earth) Ba₂Cu₃O₇ compounds superconduct at approximately equals 92 K even for magnetic rare-earth ions, but the same compounds do not superconduct when many of the same magnetic ions occupy Ba-sites, the superconductivity must originate in the charge-reservoir region, not in the cuprate planes. (3) The recent observation of photo-induced superconductivity in YBa₂Cu₃O_x, but not in La₂CuO₄, indicates the importance of charge-balance and whether the dopant oxygen is interstitial or substitutional. (4) Pair-breaking data require that a successful model be three-dimensional. (5) The observation of granular superconductivity in PrBa₂Cu₃O₇ requires a successful model to be inhomogeneous. (6) Many data require that the superconductivity originate in charge-reservoirs, rather than in cuprate planes. The following classes of models are ruled out: (1) Cu⁺²↔Cu⁺³ valence fluctuations models; (2) spin-fluctuation and d-wave pairing models; (3) hybridization and t-J models of the insulating nature of PrBa₂Cu₃O₇; (4) all models based on the charge-transfer hypothesis; (5) all two- dimensional models; and (6) all homogeneous models.