The luminescence of short period Si/Ge superlattices was systematically studied as a function of composition, strain and superlattice period. With Rutherford backscattering spectrometry the composition was determined, while X-ray diffraction was used to determine the strain and superlattice period. Two luminescence bands around 1,6 µm were observed. Etching experiments showed that the signal originated from the superlattice. Changes in wavelength and intensity were found to be related to the composition and the strain, while no clear influence of the superlattice period was observed.

Photoluminescence excitation spectroscopy of exciton transitions has been utilized to obtain information about light-holes in strained InGaAs/GaAs single quantum wells. By monitoring their behavior with respect to that of heavy-holes, it was shown possible to ascertain whether or not the quantum wells were pseudomorphic (lattice matched but strained) or relaxed and, if strained, the magnitude of strain present. Thus the indium composition of the single QW layers was deduced. This method is advantageous since it is nondestructive, requires no special sample preparation, is accurate and can readily be extended to monitoring strain in QWs subjected to various processing steps associated with device fabrication.

We have investigated the interband optical transitions within undoped pseudomorphic InyGa1-yAs/GaAs quantum wells of a range of thickness from 50Å to 150Å, and y values 0.1 to 0.2. From photoluminescence (PL), we identify the lowest interband transitions. Electron beam electroreflectance (EBER) modulation spectroscopy is utilized to detect the lowest and the higher energy interband transitions within the quantum wells. We compare the measured interband energies to those calculated theoretically.

We have observed exciton-like transitions attributable to the heavy hole and light hole levels and most importantly, confined states of the split-off valence band, not reported to date. The multiplicity of observed quantum transitions allows rectangular barrier model parametrization of these wells, using hypothetical strain splitting of the various subbands. For five such quantum wells, we find the estimated indium contents and well widths to be nearly nominal, with consistent values between independent 300K and 100K data. With respect to the heavy hole subband, the conduction band offset Qc is estimated to be 0.586 ±0.024. With suitable values, all of the transitions, including those of the splitoff band, are predicted accurately.

We have investigated the optical transitions present in MBE-grown modulation doped pseudomorphic AlxGa1-xAs/InyGa1-yAs/ GaAs HEMT structures of 120Å InGaAs thickness, y values 0 to 0.28, and x values 0.20 to 0.30. From both 300K electron beam electroreflectance (EBER) and 4K photoluminescence (PL) measurements we observe transitions from the InGaAs strained quantum well layer. The intensity and lineshape of the InGaAs transition in both optical spectra are affected by processing temperatures, and provides an indication of the quality of the HEMT.

In addition to strong, sharp features arising from the GaAs substrate and the superlattice buffer, the EBER data shows important characteristics of the AlGaAs layer which are unavailable from the PL. The latter include the presence of Franz-Keldysh oscillations, from which the crystal quality, composition, and electric field strength within the AlGaAs can be assessed. Specifically, when the growth temperatures are excessive, the disappearance of the Franz-Keldysh oscillations appears to be associated with outdiffusion of In from the strained layer, and consequent deterioration of active device performance.

We have used photoluminescence excitation and photocurrent spectroscopy to investigate the electronic properties of InxGa1-xAs/GaAs strained layer quantum wells and superlattices. In quantum wells, sharp excitonic transitions between discrete energy levels are observed both in excitation and near flatband photocurrent spectra whereas superlattices show heavy-hole to conduction miniband transitions at the Brillouin mini-zone centre and edge, directly giving the electron miniband width. Applying a longitudinal electric field to the quantum wells produces a red shift of the excitons due to the quantum confined Stark effect, while in superlattices, photocurrent spectra at finite applied electric fields show for the first time in this system, the effects of Wannier-Stark quantization. The analysis of the spectra provides a precise determination of the band offset.

Strained layers of indirect GaAsP have been grown on the (111)B-oriented surface of GaP by Metal-Organic Vapour Phase Epitaxy (MOVPE). These layers have been characterized by low-temperature photoluminescence (PL), electroreflectance (ER), secondary-ion mass spectroscopy (SIMS), and wavelength resolved imaging cathodoluminescence (CL). We have been able to follow the transition energies of the lowest X conduction band edge, as well as the higher Γ band edge of the strained layers, as a function of composition up to an As-concentration of 38 %. The experimental values of the transition energies are compared with predictions made from calculations based on deformation potential theory. CL allows us to directly observe the onset of dislocation formation, i. e. the critical thickness. The appearance and properties of the dislocation network revealed by CL are very different from those of the corresponding network when the strained layers are grown on (001)-oriented surfaces.

We have studied the photoreflectance spectrum at 300K from a GaAs/In0.5 Ga0.5p (ordered) single quantum well fabricated by atomic layer epitaxy. Comparison of the energies of the observed intersubband and barrier transitions with an envelope function model calculation yields a valence band offset of 350 ± 20 meV.

InSb has been grown on semi-insulating GaAs substrates by molecular beam epitaxy. By growing an InSb buffer layer at 300 C prior to the main InSb layer growth at 420 C, the effect of the 14% lattice mismatch between GaAs and InSb was minimized. A typical 5 µrn InSb film had a room temperature carrier concentration and electron Hall mobility of 2 × 1016/cm3 and 6×104 cm2/Vs, respectively. At 77 K these values became 2 × 1015/cm3 and 1.1 ×105 cm2/Vs. Temperature dependent Hall measurements revealed a peak in the mobility at 85 K and 70 K for the 5 and 10 µm samples. Capacitance-voltage measurements using MIS capacitors produced 77 K carrier concentrations in agreement with the low fieldHall measurements. Carrier lifetimes were determined by photoconductive response measurements. Lifetimes of 20 ns and 50 ns were determined for the 5 and 10 µm films. For comparison, the carrier lifetime in bulk n-type InSb was found to be 200 ns. Optical characterization by room temperature IR transmission spectroscopy showed a broad absorption edge, with an absorption coefficient of 1.4 × 103/cm at a wavelength of 6 µm. Epilayer thickness was determined from observed interference fringes. Raman spectroscopy showed that each epitaxial layer had a spectrum equivalent to that of bulk InSb.

We report low temperature magneto-photoluminescence(PL) investigations of ex-citon spectra of n-doped (AlGa)As-GaAs single heterojunctions. At zero field, the PL spectrum is dominated by the free excitons and excitons bound to the impurities in the bulk GaAs, which overlap a weak emission band associated with the radiative transition between the two dimensional electron gas(2DEG) and the photoexcited holes. In the presence of a magnetic field applied parallel to the growth axis the transitions from the 2DEG, now quantized into Landau levels, become well pronounced. Additionally, intensity oscillations are observed when the 2DEG line crosses the exciton lines, which we believe is due to the effect of a resonant tunneling of the 2DEG from the quantum well region to the bulk GaAs.

High pressure photoluminescence measurements on modulation doped GaAs-AlGaAs quantum well structures have been performed for the first time with applied magnetic fields up to 15 Tesla. We have observed Landau fans from interband transitions of the 2D free electron gas between 0 and 8.5 kbar. In this pressure range the electron effective mass in GaAs increased at the rate of 2.6% per kbar. Above 9 kbar, the free Landau transitions disappeared and bound magneto-exiton behaviour dominated the spectrum. The influence of pressure on the band-gaps causes a controlled trapping of the free electron from the GaAs well to Si donors (DX centers) in the AlGaAs layers. Above 9 kbar the pressure coefficient of the GaAs band gap was found to be 10.4 meV/kbar which is comparable to the accepted value in undoped GaAs quantum well structures.

The radiative recombination of two-dimensional (2D) carriers in an n-channel GaAs/AIGaAs heterojunction has been studied with time resolved photoluminescence (PL). Two bands related to the recombination of 2D carriers, the so called H-band 1 (HB1) and H-band 2 (HB2), are observed in PL. The spectral shape and position is strongly dependent on the sample and the experimental conditions. The H-bands are e.g. found to shift within a large energy range with the excitation intensity. We report here on the dependence of the decay times of the H-bands on their spectral position. The results are consistent with a recombination process involving 2D electrons, confined in the interface notch, and three-dimensional (3D) holes either from the valence band (HB1) or from neutral acceptors (HB2) in the active GaAs layer. The decay times of HB1 are found to vary in the range of 2-100 ns, while the corresponding decay times of HB2 are in the range of 100 ns - 10 µs.

We report on a study of hot-carrier effects on optical properties of GaAs/AlxGa1-xAs quantum wells, by photoluminescence (PL) spectroscopy in the presence of a microwave (MW) field. Both doped and undoped, multiple quantum wells (MQWs) and single quantum wells (SQWs), grown by molecular beam epitaxy (MBE), show a profound enhancement of free exciton (FE) and bound exciton (BE) (for the doped wells) PL emissions with MW irradiation. This is attributed to effects of hot-carriers induced by the MW electric field. The mechanism responsible for the strong enhancement in PL intensity of the QWs in the presence of hot-carriers is studied, and is discussed in terms of an enhanced carrier trapping by the QWs as a consequence of the MW-induced heating of the photo-excited free carriers in the AlxGa1-xAs barriers.

We applied ellipsometry to characterize layers of InxGa1-xAs grown by molecular beam epitaxy on (001) InP. Samples with mismatched layers exhibit significant anisotropy in the index of refraction. We explain these observations by the presence of misfit dislocations which form in an asymmetric pattern. This results in asymmetric strain and, via piezo-optical effects, an anisotropy in the optical properties. This effect makes ellipsometry a more sensitive technique than double-crystal x-ray diffraction for detecting misfit dislocations in these heterostructures.

Variable angle spectroscopic ellipsometry (VASE) was used to characterize a 20 period GaAs/Al(x)Ga(1-x)As multiple quantum well structure, grown by molecular beam epitaxy. The barriers were nominally 200 Å Al(.25)Ga(.75)As, and the well regions were grown to approximate a linearly graded composition, from x=0 to x=0.25, with total well width 200 Å. VASE data in the E1, E1,+Δ1. region were analyzed using four different models. It was founcЃ that the dielectric function of the cap GaAs layer was shifted to higher energy with respect to the bulk GaAs dielectric function.

Local stress measurement is becoming very important to evaluate electrical and reliability property of semiconductor. Raman spectroscopic method has been established to measure local stress at the area of one micron in diameter. The measurement problems came from the characteristics of a spectrometer have been solved by the following.

–Ar Plasma line is utilized to calibrate wave numbers.

–Gaussian and Lorentz distribution are utilized to determine the peaks of Plasma line and RAMAN shift.

This method with introduction of a certain assumption can be applied to the stress measurement not only for Silicon single crystal like trench structure, but for deposited thin layers like silicon oxide or silicon nitride, and plastic packaging material.

This paper describes the measurement methods of local stress, data processing techniques of measurement data and several examples of the measurement on a semiconductor thin layer and packaging plastic.

In an epi-layer of GaAs less than 300nm to 100nm thick grown on silicon substrate by two-step MOCVD lethod, broad Raman scattering centered at 700cm-1(L+) and TO-like phonon at 268cm-1(L-1) were observed as well as LO phonon spectrum (292cm -1) in a back-scattering optical geometry. Emission peak of photoluminescence spectra in these epilayer of GaAs were found to shift by 33meV at 300K towards high energy side. In a thin buffer layer of GaAs less than 20nm thick, however, Raman spectra showed only LO phonon peak. These experimental facts shows n-carrier generation of 1018cm-3 only within interfacial epi-layer of GaAs less than 300nm thick, except for the very thin buffer layer of GaAs, because of incorporation of silicon atoms during growth of epilayer at 700°C. In addition, in both layers of GaAs less than 300nm, compressive stress of 109dyn·cm-2 was observed, which were found to relax abruptly with thickness.

The new technique of metalorganic magnetron sputtering (MOMS) produces high-quality (100) epitaxial InSb films on (100) GaAs substrates, despite the large 14.6% lattice mismatch between InSb and GaAs. We have used Raman scattering to examine MOMS-grown InSb films of thicknesses 0.17 - 2.67 µm, and commercial bulk InSb. We observe the longitudinal optical (LO) phonon peak, and the second order 2LO peak, which is enhanced by outgoing resonance with the E1 + Δ1, gap of InSb. The half-widths and intensities of these bands are related to sample quality as a function of film thickness and to the role of biaxial stress in the InSb film.

In optical experiments with laterally patterned modulation-doped GaAs/AlGaAs quantum wells we observe spatially separate confinement of electrons and holes to one-dimensional quantum wires. We determine the one-dimensional subband spacing and Fermi energy from inelastic light scattering and photoluminescence spectra. From these measurements we directly determine the one-dimensional electron density.

The pressure coefficients (α) of the excitonic transitions arising from the conduction (CB) to the heavy (HH) and light (LH) hole sub-bands of a GaSb-AlSb multiple quantum well structure (MQW) grown on a GaAs substrate are determined. Photoreflectance (PR) and Photoluminescence (PL) studies are employed at cryogenic temperatures. The α for the ground sub-band transition is ~10% smaller than that for bulk GaSb. This effect is explained by in-plane deformation of the MQW arising from the substrate under external pressure. On the other hand, the α get progressively smaller for the higher sub-band transitions due to quantum confinement The PL intensity drops dramatically as the direct Γ CB crosses the L CB at ~10kBars but the PR intensity persists until the X CB crosses each sub-band energy.

High electron mobility transistors (HEMTs) with single quantum well active layers composed of pseudomorphic IπGaAs grown on GaAs and InP are establishing new standards of performance for microwave and millimeter wave applications. This is due to recent progress in the molecular beam epitaxial growth of strained InGaAs heterostructures coupled with developments in short gate length (sub%0.2 µm) device fabrication technology. This paper reviews this progress and the current state-of-the-art for materials and devices.