Application of high resolution photoluminescence and absorption spectroscopies to characterize the semiconductor quantum well structures and alloys is reviewed. In particular, two main topics are discussed. First, the dependence of the width of the excitonic transitions in semiconductor alloys as a function of alloy composition is described. The dominant line broadening mechanism in these alloys arises from the statistical potential fluctuations caused by the components of the alloy. Second, the behavior of the width of the excitonic transitions in semiconductor quantum well structures as a function of the interface quality and the well size is discussed. A model of the relationship of the linewidth with the interface roughness is described. Recent calculations of the excitonic linewidths in semiconductor alloys and quantum well structures are briefly reviewed. Results of these calculations are compared with the available experiment data in GaAs/AlGaAs, InGaAs/InP and InGaAs/InAlAs systems. It is shown that the use of appropriate theoretical models in conjunction with the measurements of excitonic linewidths in these systems leads to a fairly reliable information concerning the microscopic structure of the interfaces and of the extent of the compositional disorder in constituent alloys.

Photothermal spectroscopy employs the small rise in temperature associated with the absorption of electromagnetic radiation to probe optical and transport properties of materials. A review of the various photothermal detection schemes is given, and examples which illustrate the power of this technique are reviewed.

This paper reports on a computer-controlled system which has been designed for mapping photoluminescence (PL) intensities of GaAs wafers or epitaxial layers up to 3 inches in diameter. In this instrument, the excitation source may be moved at right angles to the sample surface without any change in the collection efficiency of the PL light. The PL intensities are measured at 2 mm intervals to reveal the homogeneity of the surface. Possible operating temperatures range from 4K to room temperature. The effectiveness of the system is demonstrated on Liquid-Encapsulated Czochralski (LEC), Horizontal Bridgman (HB) and epitaxial GaAs samples. This PL scanning technique shows the intensity variation in these samples to be closely related to the defect density distribution.

Conventional photoluminescence (PL) and selectively-excited photoluminescence (SPL) techniques have been employed in order to identify donor species giving rise to features in the near-band-gap emission from ZnSe epitaxial layers grown on GaAs substrates by molecular beam epitaxy (MBE). Specifically, we have been interested in understanding the origins of the I20 and Ix peaks observed in MBE-grown ZnSe in several labs. A number of different impurity species have been identified on the basis of the energies of two-electron transition satellite peaks observed under resonant excitation into the donor-bound exciton manifold in the SPL experiments. Secondary ion mass spectrometer (SIMS) measurements have been performed on the same samples to provide supporting evidence for our assignments.We fins that some impurities which appear in SIMS only at their detectability limits (<10¹⁴ cm in some cases) can contribute significantly to the PL emission spectra. Implications of this study for improving the quality of MBE-grown films will be discussed.

An optical transient reflectance technique has been developed to characterize both the thermal and elastic properties of thin film materials. By using picosecond duration laser pulses, films on the order of 100 nm thick can be studied. Measurements of the thermal diffusivity, interfacial thermal impedance and acoustic velocity in thin, supported metal films are discussed.

We have employed photoluminescence measurements at 10-300°K to study the effects of deposition parame-ters, surfaces preparation and heat treatment on the properties of CdTe polycristalline thin films. The films were grown using a modified hot wall close spaced vapor transport system. We found strong differences in the photoluminescence spectra of samples grown under different conditions. Heat treatments in the as-grown samples increase the average particle size and reduce the native defect density.

Multiple peaks, recently observed in the low temperature photoluminescence (PL) spectra of GaAs/AlGaAs single quantum wells fabricated by momentarily interrupting the molecular beam epitaxial growth between adjacent but different semiconductor layers, have been interpreted as originating within smooth regions in the quantum well layer differing in width by exactly one monolayer. We have observed similar structure in similarly grown samples but find that low temperature PL can be misleading. However, higher temperature PL or PL excitation spectroscopy do provide unambiguous evidence for the model of interface smoothing due to growth interruption. Further, time-resolved spectra yield decay times of the individual peaks which are consistent with this interpretation.

The imaging cathodoluminescence capability of a scanning electron microscope has been complemented by a spectral filtering technique to study the spatial origin of photoluminescence from CdTe at 77K. The intent of this work is to resolve the spatial origin of different luminescence spectral components in different regions of the crystal (e.g., midgrain, near-grain boundary, etc.). The results indicate different spatial locations for the exciton and the defect photoluminescence lines, and the association of bound exciton lines with clustered dislocations. Furthermore, the exciton line appears to originate from two different regions of the sample, which may imply bound excitons from two different binding sites. We infer from the present study that the criterion generally adopted, that a high bound exciton band intensity and a relatively low defect band intensity implies good crystal quality, may be ambiguous.

We present (I) low temperature excitation-wavelength-dependent photoluminescence studies in GaAs/AlxGai-xAs quantum well structures, which reveal the well thickness variations along the MBE growth direction, and (II) the photoluminescence excitation spectroscopy work carried out in the region of unconfined transitions with a series of GaAs/AlxGal-xAs superlattices which have a fixed well size and aluminum concentration in the barrier. We have found that the changes in the barrier widths of the superlattice samples can drastically affect the strengths and energies of the unconfined transitions.

We report the first observation of a narrow, low temperature photoluminescence peak associated with the presence of a two-dimensional electron gas (2DEG) at a GaAs/AlGaAs heterointerface. The exact physical mechanism giving rise to this emission is not clear. However, based on a large number of samples, its intensity is found to be directly related with the concentration of the electron gas. The temperature and exciting-intensity dependencies of the peak are consistent with a model based on free excitons in GaAs bound to the electron quantum well formed at the heterointerface by the 2DEG.

GaAs/A1xGa1-xAs single quantum wells (SQW)of width in the range of 20-40Å are probed by monitoring the luminescence and stimulated emission spectra under intense photoexcitation. The emission is due to the radiative recombination of an electron-hole plasma (EHP). Its density (n) and effective temperature (Teff) are obtained by model fitting the photoluminescence band shape. We find that in the ambient temperature range 4K-220K the carrier concentration is increasing with temperature from 10¹¹ to 10¹³cm^-2. The optical gain of the stimulated emission(SE)was measured by the variable stripe length method. A comparison with gain values measured in bulk GaAs under the same excitation conditions shows that the EHP in the SQW is about 20 times denser than in the bulk. The appearence of stimulated emission only at the lowest energy of the emission spectrum (where the unexcited crystal is transparent) means that only a fraction of the illuminated volume is filled by the EHP.

The optical characterization technique of photoreflectance (PR) has been modified by replacing the source of the probe light with a dye laser. This has allowed easy access to temperatures below 100K, a temperature range in which it was previously difficult to measure a PR spectrum. This system is also capable of simultaneous photoluminescence excitation spectroscopy (PLE). The combined PR/PLE apparatus has allowed us to obtain information regarding the nature of the PR signal.

We have investigated the electroreflectance (ER) and photoreflectance (PR) spectra from the space charge region (SCR) of the model Schottky barrier system indium-tin-oxide on p-InP (ITO/InP). Both ER and PR were studied as a function of reverse dc bias, V_bias. The observed Franz-Keldysh oscillations (FKO) provide a direct measure of the surface dc electric field, εsdc. In ER the ac modulating voltage (for small modulation) effects only the envelope of the FKO but not the period. A generalized Franz-Keldysh theory, taking into consideration large built-in dc fields, is presented which accounts for the above experimental results. From a plot of (Eac)2 as a function of Vbias we have obtained the built-in potential and net carrier concentration of the device. Our work demonstrates that electromodulation in Schottky barriers can be used as an optical Mott-Schottky method.

Photoreflectance (PR) and electroreflectance (ER) responses were compared on samples of GaAs in order to establish a detailed relation between the two techniques. The majority of experiments were made on an n-GaAs Schottky Barrier in the vicinity of the fundamental edge (1.4 eV). PR spectra were studied as a function of DC bias with the modulation obtained by chopped laser radiation. A complementary set of ER measurements were made over the same bias range, and a comparison was made of ER response with and without CW laser illumination. This yielded a direct relationship between CW laser power and an equivalent effective bias representing the laser irradiation reduction of the band bending. The correspon-dence between ER and PR allowed us to calculate the average electric field in the depletion layer based on the Franz-Keldysh oscillations present in both spectra. Aspnes and Studna (1973) have shown that the slope of the plot of the energy value of the oscillation extremum index n yields the average electric field provided that the interband effective masses are known. This result indicates that PR can determine submerged interfacial fields with-out any electrical contact to the sample.

The optical transitions near the band gap energy E0 have been obtained by photoreflectance (PR) measurements on GaAs and CdTe single crystals, various epitaxially grown AlxGai_xAs layers, and GaAs-AlGaAs quantum well and superlattice structures. The PR spectra have been analyzed to determine the behavior of the E0 values and lineshape parameters at different alloy compositions and structural periodicities for the multilayer materials. The alloy compositions derived from the PR data are shown to be consistent with the values obtained by Raman and x-ray diffraction measurements on the same samples. PR is also found to be a convenient method to study the effects of ion implantation and subsequent annealing treatments on the structural and electronic properties of GaAs and CdTe. The incomplete recoveries of the PR spectra following thermal anneals at 500°C and 850°C for CdTe and GaAs, respectively, suggest these treatments are only partially effective in reducing the lattice damage caused by these implants.

When heterostructures of semiconductors are subjected to an alternating strain, the piezomodulated optical properties, as in the bulk, display signatures characteristic of electronic transitions. We have applied the piezomodulation technique to the electronic transitions associated with GaAs/Al_xGa_{i_x}As quantum well structures. Our results obtained at temperatures down to that of liquid helium with single-, double-, and multiple-quantum wells reveal electronic transitions in the wells, the barriers and the buffer layer with exceptional clarity. The effects of coupling in the double and multiple quantum wells are clearly identified. Relative advantages and limitations of the piezomodulation and the now well-established photomodulation techniques'are discussed on the basis of experimental results on identical samples under comparable experimental conditions.

This paper reports investigations of ZnS quasi-amorphous films by electroreflectance (ER). The films were produced by thermal evaporation and their structure determined by electron diffraction. A voltage Vo cos cut was applied through the film with two evaporated Al electrodes. A lock-in amplifier gave 2 signals, Sf at f=ω/2π frequency and S2f at 2f frequency. The S2f spectrum, characteristic of the centrosymmetric bulk component of the film, reveals tails of localized states typical of amorphous semi-conductors. The Sf spectrum, characteristic of the interface layers with broken centro-symmetry, reveals tails of impurity levels which we attributed to diffusion of the electrode metal into the semiconductor.

We have studied for the first time the optical properties of GaAs/Al_xGa_1-xAsAs multiple quantum wells (MQWs) grown on Si and Ge substrates and InyGai-yAs/GaAs strained layer MQWs grown on Si substrates by photoreflectance. These preliminary results show that good quality epilayers from different semiconductors can be grown on non-polar substrates indicating the possibility of new device materials besides their importance in fundamental research. The experimental data were compared with calculations based on envelope-function approximation and fit to third-derivative functional form of reflectance modulation theory.

Several GaAs-piezoelectric transducer configurations have been characterized to increase the sensitivity of a direct-coupled photoacoustic spectrometer constructed to study the optical properties of GaAs. We have shown that the use of an annular-shaped transducer and the presence of a thin mirror between the GaAs and the transducer decrease spectrometer noise and allow for enhanced sensitivity through the exploitation of transducer resonances. Limitations of this technique for studying semiconductor deep levels are identified and the use of the complex modes of the transducer for studying semiconductor heterostructures is discussed.

A coincident CW microwave beam and pulsed optical beam have been used to observe recom-bination and trapping mechanisms in semiconductor wafers. A GaAs laser (904nm), AlGaAs laser (850nm) and xenon flash lamp (spectral peak at 550nm) have been used to generate mobile carriers throughout GaAs wafers by excitation from impurity levels, to generate electron-hole pairs within a micron of the surface by band-to-band generation and to generate electron-hole pairs within one-tenth micron of the surface respectively. By observing the peak amplitude of the photoresponse and the transient decay, information about deep levels in semi-insulating (S.I.) GaAs wafers and doped channel layers (as well as surface recombination levels) can be obtained. Results are presented on undoped liquid encapsulated Czochralski (LEC) wafers, with and without implanted channels from many vendors. Less extensive comparisons with chromium-doped LEC wafers with epitaxially-grown channels, chromium-doped LEC wafers and undoped horizontal gradient freeze (HGF) S.I. wafers are presented, along with initial wafer mapping and variable temperature results on S.I. wafers with GaAs laser excitation.

An optical analog of Electron Beam Induced Current (EBIC) technique called laser beam induced current (LBIC) has been developed and utilized to obtain maps of electrically active defects in semiconductor materials. We have demonstrated the use of LBIC for spatial evaluation of LPE HgCdTe and for characterizing HgCdTe p-n junction detector arrays, in a non-destructive way without making any electrical contacts to individual detector elements.

We present the infrared wavelength-modulation spectra of molecular-beam-epitaxy- (MBE) and liquid-phase-epitaxy- (LPE) grown Ini_xGaxAs (0.45 < x < 0.50) epilayers on (100) InP substrates. The transmittance, reflectance, and their wavelength derivatives are measured in the neighborhood of the band gap at room temperature. The dependence of band gap on strain is presented and analyzed. It is shown that epilayers partially relax the interfacial strain according to their thickness, giving different dependences of band gap on alloy composition. The results are analyzed by introducing a normalized fractional-strain parameter and applying Hooke's-law elasticity and deformation potential theories.

Electrically active flaws near the surface of silicon wafers generally impair the successful manufacture of integrated circuits. Detrimental defects such as stacking faults, dislocations, and metallic precipitates are often 1-2 microns in size. Thus, a defect detection system would need to exhibit both high spatial resolution and contrast at defective sites. Several approaches for defect detection are in use, although no technique appears capable of non-destructively detecting 1 micron defects in silicon, without vacuum, in a timely manner. A pump-probe laser system has been developed to satisfy these requirements.

When Ga or Al atoms are supplied on a clean GaAs surface under As-free or low As pressure atomosphere, they are quite mobile and migrate very rapidly on the growing surface. This characteristic was utilized for growing atomically-flat GaAs-AlGaAs heter-interfaces, and for lowering the growth temperature. The method is based on metal-organic chemical vaper deposition and employs alternate supply of gaseous sources. (AlAs)n(GaAs) superlattices and AlGaAs-GaAs single quantum wells were grown using this method, and characterized with X-ray diffraction, photoluminescence, and Raman scattering measurement. These measurements revealed improved flatness of AlGaAs-GaAs heterojunction interfaces grown by this method.

The Raman spectrum of semiconductors is sensitive to changes in the structural, mechanical and electrical properties. We report results obtained with the Raman microprobe after laser processing or damage of semiconductor thin films. The spatial resolution in our experiments has allowed the observation of unsuspected modifications.

The use of Raman spectroscopy to characterize thin silicon films formed by laser recrystallization using different capping layers, thin silicon films formed by plasma deposition, and thin films of tungsten silicide formed by rapid thermal annealing is reported.

The applications of Raman spectroscopy to study semiconductor interfaces and the initial phases of interface formation is described. The limitations of weak signal from interface structures has proved a severe limitation, but it has recently been shown that multi-layered thin film structures can be made which utilyze optical interference properties to enhance the Raman scattering from thin films and thin film interfaces. This technique (termed IERS) has been applied to study several metal-Silicon interfaces. An even more difficult problem is the study of interface formation during ultra high vacuum (UHV) deposition on atomically clean surfaces. The experimental considerations from in situ UHV Raman scattering will be described. The results of Raman scattering for the interface of Pd deposited on crystalline and amorphous Si are presented. Both the IERS and in situ UHV measurements are used to explore the mechanisms of silicide formation.

The characterization of plasma-assisted CVD thin films of nanocrystalline (nc)-silicon using Raman and optical spectroscopy, is described. Characteristic variations of the frequency and linewidth of the Γ25, Raman-active mode of silicon occur due to phonon localization in the quasi-isolated crystallites. In addition, a grain-boundary mode and variable Raman and elastic scattering intensity enhancement at the grain boundary regions, have been observed. The light scattering enhancement scales very well, as a function of average crystallite size and compressive stress in the films, with the optical absorption coefficient and the intensity of the x-ray diffraction component attributed to the expanded grain boundary regions. The finite crystallite size effect in nc-silicon is compared briefly with Raman results on semiconducting, nc-selenium particles.

High-quality monocrystalline beta-SiC thin films were grown via two-step process of conversion of the Si(1002) surface by reaction with C2H4 and the subsequent chemical vapor deposition (CVD) at 1360 C and 1 atm total pressure. Four dopants, B and Al for p-type and N and P for n-type, were also incorporated into monocrystalline beta-SiC thin films during the CVD growth process. IR and Raman spectroscopies were used to evaluate the quality of the undoped beta-SiC thin films and to investigate the effects of dopants on the structure of the doped beta-SiC thin films. The changes in the shapes of IR and Raman spectra of the doped thin films due to dopants were observed. But the XTEM micrographs except for the B-doped and annealed films showed the same density and distribution of stacking faults and dislocations as was seen in the undoped samples. The IR and Raman spectra of the B-doped and annealed films showed the broad and weak bands and one extra peak at 850cm71 respectively. The SAD pattern and XTEM micrograph of the B-doped and annealed film provided the evidence for twinning.

We have investigated symmetry forbidden longitudinal optic Raman scattering for various polarization configurations at 4579A from the <100> surface of heavily doped n-GaAs caused by the strong surface-fields and high impurity levels. We have evaluated the magnitude and phase of the coefficient of the electric-field induced term as well as the magnitude of the coefficient of the impurity-induced factor. The former parameter may be very useful for the contactless evaluation of space charge electric fields in GaAs.

We report infrared reflectance spectra in the range 100-450 cm^-1 for an AlAs-GaAs heterostructure and three AlAs-GaAs superlattices with different periods. All the spectra clearly exhibit the TO phonon modes of pure GaAs and AlAs and a sharp interference peak at the GaAs LO frequency. The heterostructure data yield a set of phonon parameters for unoxidised AlAs. The superlattice spectra exhibit additional structure between 225 and 400 cm^-1 and a broadening of the GaAs TO peak. The long wavelength superlattice optical theory of Agranovich and Kravtsov explains most of the features of the superlattice reflectivity.

The use of IR reflectance measurements to study the properties of the insulating and surrounding layers obtained by implanting nitrogen into silicon is discussed. IR spectrometry yields not only information on the types and quantity of bonds in the implanted layer, but is also employed to determine other physical parameters of the layered structure. A model to simulate IR-reflectance measurements and extract parameters from it has been developed. The implanted wafer is modelled by a multilayered structure employing matrix methods in the analysis. The absorption peaks are represented by simple Lorentzian oscillators. IR reflectance spectra of the as-implanted and annealed samples were studied. The measured spectra were then compared with the model.

Presented here is a brief review of the dominant features of quantum wells and superlattices that are seen in light scattering spectra, and how these can provide quantitative and qualitative information about the structures. These features include effects of acoustic phonon zone folding, optical phonon quantum levels, peak intensity variation due to interface disorder, scattering resonances at quantized electronic gaps, and peaks due to transitions between electronic levels in modulation doped structures. Quantitative information obtained includes layer periods, well widths, and electronic level energies. Some conclusions can also be made concerning structural disorder, interface broadening, and the amount of strain in lattice mismatched systems.

The characterization of materials for semiconductor applications has been significantly advanced by the use of photoluminescence and laser-Raman spectroscopy. Photoluminescence is particularly sensitive for identifying impurities and mapping wafers to determine the distribution of dislocation densities over the surface of a wafer. Direct correlation with the threshold voltages of finished devices is one of the practical applications of such data. Laser-Raman spectroscopy can identify surface contaminants and determine lattice disorders, residual strain and free-carrier density. beparate, dedicated systems are normally required for each analytical technique. In this paper, the authors describe a new and totally automated system that incorporates both photoluminescence and Raman capabilities. Wafers up to 4 inches in diameter were characterized at room temperature and while cooled by liquid helium. Sample materials included 8i, GaAs, LiNb0 and InP. Information from spectra, wafer maps and peak shifts is presented and discussed. The efficiency or semiconductor device designs and their mass production depends largely on the quality of information charcterizing the materials from which devices are fabricated. In recent years, spectroscpy has emerged as a primary source of such information for both fundamental research and quality control in manufacturing. There are many reasons for this expanding recognition, not the least of which is the non-contact and non-destructive nature of spectroscopic analysis. Capable of being fully automated through microprocessor control, spectroscopy also generates a range of data unmatched by other methods. And among the spectroscopic techniques currently available, photoluminescence and Raman spectroscopy are especially effective for characterizing semiconductor materials like silicon, gallium arsenide or indium phosphide. basically, photoluminescence (PL) involves exciting a sample with laser light and observing any t'!mission, Besides providing a measure of crystal quality, photoluminescence has been used extensively to study the role of dopants in the production of semi-insulating GaAs and InP. In the evaluation of ion-implanted III-V semiconductors, photoluminescence has been employed to assess distribution of impurities, surface degradation from implantation and annealing, as well as lattice reconstruction during annealing. human spectroscopy complements photoluminescence characterization by providing a more comprehensive structural and molecular picture of semiconductor materials. The important parameters of a Raman semiconductor spectrum are the peak position and line shape of the lattice modes designated longitudinal optic (LO) and transverse optic 0'0). Raman measurement of these parameters can be correlated with factors integral to the successful manufacture of conventional silicon devices or devices made from faster materials like gallium arsenide.

In this work it is shown that the optical characterization of doped semiconductor layers can give important information particularly on the main properties of the free carriers. In particular, a measurement of the p-polarized light reflected from doped Si films epitaxially grown on Si substrates is shown to give information on the free carrier concentration and also on the effective mass. Data on Pt Silicides are also reported.

Infrared reflectance spectroscopy, in the range of 4000 to 250 cm^-1, has been used to non-destructively characterize the carrier concentration and thickness of n-type epitaxial GaN and AlGai_xAs and S-doped bulk InP. Measurements of carrier concentration and thickness uncertain to 2-4% and 2 % are typical and relative differences of 2 and 1% respectively can be observed from different areas of the sample. This reflectance tool is sensitive to carrier concentrations above about 1 x 10¹⁷cm-for the semicondu9tors studied here and is estimated to be sensitive to concentrations in the low 10 cm range for the heavier III-V's, e.g., GaSb and InSb. A by-product of these measurements has been the improvement of an organometallic vapor phase epitaxy system with minimal interruption to the growth program because of the quick turn-around time of this technique.

Picosecond transient reflectivity was applied to measure surface recombination processes in intrinsic and n-doped GaAs. Photowashed surfaces were characterized by slow recombination and the results imply flat band conditions were achieved. Unwashed samples are characterized by rapid, complex surface charge carrier kinetics.

We have applied in situ ellipsometry to characterize the initial nucleation, interface structure, and surface roughness evolution of thin film hydrogenated amorphous silicon (a-Si:H) and related materials prepared both by rf glow discharge and by ion beam sputtering. Selected areas will be covered where in situ ellipsometry has made an impact on our understanding of the growth mechanisms for these thin films. The in situ measurements have been performed using a 3.4 eV incident probe beam. At this photon energy, a-Si:H is strongly absorbing, and the interpretation of the data is simplified since material only within the penetration depth of the light is probed. Topics to be discussed include: (1) the influence of deposition technique and parameters on the initial nucleation of a-Si:H on c-Si substrates. (2) the evolution of surface roughness in the later stages of growth of a-Si:H, and (3) the effect of deposition procedure on the interface properties of glow discharge amorphous silicon/amorphous silicon-nitrogen heterostructures.

Determination of the compositional depth profile of an inhomogeneous film structure is often approached via surface analysis techniques used in a sputter depth profiling mode. An alternative is to model the compositional profile to fit optical measurement data, such as multiple incident angle or spectroscopic ellipsometric data. This paper presents the application of a statistical approach to this analysis problem. Multiple incident angle and multiple wavelength ellipsometer measurements have been made on hafnia and alumina single films on borosilicate glass substrates. Theoretical sensitivity data of the measured quantities T, A on the index and thickness of the film is presented and discussed. The measurement data is then numerically fit to several models that express small inhomogeneities in the film refractive index as a system of multiple homogeneous films. Existence of local minima in the value of the chosen merit function and statistical techniques that permit location of the global minimum are addressed by 'this approach. Results are discussed in terms of the magnitude of the merit function and compared to spectral reflectance measurements made on the coated samples.

We observe two-photon absorption (2PA) of picosecond, 0.6 μm, 0.25 nJ pulses in a 0.4 μm film of ZnSe. We use high-frequency modulation phase- sensitive detection to be near the shot noise limit, followed by a low frequency pulse delay modulation to discriminate against large thermal nonlinearities. This dual modulation technique, combined with the field enhancement produced by placing the film in a resonant cavity, allows observation of 2PA and other fast nonlinearities using pulses having peak powers of the order of a Watt.

Moving spot illuminated semiconductor panels are used in millimeter wave image convertors. In order to know the performance of this system it is required to know the response of illuminated semiconductor panels. In this paper reflected millimeter power from moving strip illuminated semiconductor panels as a function of scanning velocity, width of the strip, time etc. are studied.

We introduce the Resonant ATR technique, a new non-destructive technique for the characterization of multilayer structures in terms of the thickness and composition of the various layers. After a review of the basic principles, the technique is exemplified through its application to the layer thickness determination of wafers used in the manufacture of heterostructure lasers.