The present work deal with the coarse contrast modulation along the <010> directions observed in (100) planar view TEM observations of In0.52Al0.48As layers grown on InP substrates at temperatures higher than 550°C. The most important features of these contrast inhomogeneites are briefly reviewed. Besides, the appearance of the contrast in [011] cross-sectioned specimens is presented and its origin related to precipitates at the layer-substrate interface. The density of precipitates (ρp) has been found to increase as Tg rises, and an approximate value of the activation energy needed to induce the precipitation has been derived from the correlation of ρp and Tg.

Recently, conventional wisdom has reversed its view on the disadvantages of strain in active semiconductor devices. Now lattice-mismatch-induced biaxial strain is being actively studied as a technique for optimizing bulk and quantum well (QW) device performance. It has been realized that, in addition to permitting once inaccessible energy ranges to be reached, strain has the potential of altering the properties of energy bands in a precise and advantageous manner provided that care is taken that the strain remain pseudomorphic (i.e., that the critical thickness, beyond which the layer relaxes with detrimental effects on quality, not be exceeded).

This paper reviews progress in this field including techniques for determining the magnitude of pseudomorphic strain in single QWs, and recent theory and experiments detailing the advantages which strain, both compressive and tensile, can bring to QW laser diodes. The use of strain to balance the polarization anisotropy inherent in QW structures is also discussed. Finally, a novel use of biaxial tensile strain in the barriers of QW devices to minimize polarization sensitivity is introduced. The idea is to create a structure in which the light and heavy hole valence bands are degenerate, as in bulk material, but which still retains the advantages of QWs (higher quantum and differential quantum efficiency, etc.).

We report a study of interfacial quality of strained-layer InGaAs/GaAs quantum well lasers grown by gas-source molecular beam epitaxy. It was found that the growth temperature (Tgr) of the InGaAs layer plays an important role in the interfacial quality. For Tgr < 515 °C, a large amount of non-radiative recombination centers is likely to exist in the InGaAs/GaAs quantum well, which can be attributed to the presence of vacancies and atom clusters and lattice misfit defects. For Tgr > 515 °C, the InGaAs/GaAs interfaces show significant roughness due to In segregation. Rapid thermal annealing grades the InGaAs/GaAs interface because of interdiffusion of group-III atoms at the interface, and removes most of the non-radiative recombination centers from the low Tgr (<515 °C) samples. In addition, we observed that the interfacial quality of the InGaAs/GaAs quantum well shows no strong dependence on (100) vicinal orientations of GaAs substrate.

AlGaAs/InGaAs/GaAs heteroepitaxial layers grown by molecular beam epitaxy were studied by cross-sectional transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The presence of waviness/roughness, fine periodic striation contrast due to Al composition oscillations, and defects were observed by TEM in selected samples. EDS on the TEM was of limited utility in determining the composition of thin epitaxial layers and in comparing the composition near and away from a defect. Arguments are presented to rationalize these results.

Heavily carbon doped ρ-type GaAs/In0.3Ga0.7 As strained-layer superlattices (SLSs) with hole concentrations as high as 1 × 1020 / cm3 were successfully grown for the first time by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic and solid indium. The single quantum well (SQW) and multiple quantum well (MQW) structures with different well width from 2 to 16nm were also designed to analyse the strain relaxation. The experimental results show that the SLS structures made of heavily carbon doped ρ—type GaAs and InGaAs have both of high hole concentration and small effective bandgap, which are satisfied for the application in heterojunction bipolar transistors (HBTs) as base layer.

In this work we report on detailed temperature dependent photoluminescence measures on InGaAs/GaAs strained layer quantum well structures. Excitation energies above and below the GaAs band gap have been used in order to separate the contributions of the carrier trapping to the generation-recombination processes from the recombination mechanisms proper of the quantum wells. The results show that a decrease of the trapping efficiency contributes to the photoluminescence quenching, and suggest that the strong photoluminescence quenching observed in these structures should be mainly attributed to defects present in the quantum wells. A clear dependence of the luminescence quenching on the excitation intensity has also been found.

Using the envelope function formalism and the effective mass thecry, we have studied the E(k) energy dispersion and the confinement energies of the lower lying conduction band and the higher lying valence bands states in GaAs /GaAlAs Single Qantum Well (SQW) structures grown on GaAs substrates with different orientations of the growth axis :(001),(111),and (113). Then, the valence subbands dispersions are calculated away from the zone center for a given well width and under uniaxial stress for the three different growth directions

The relaxation of thermal stresses during the Czochralsky growth leads to frozen in deformations in the boules. These deformations lead to a nonintentional inhomogeneous miscut of the wafers. From the X-ray double crystal measurement of frozen in deformations in GaAs bulk crystals a nonintentional miscut of about 10−4 may be estimated. The measurement of the misorientation distribution over a LEC GaAs wafer yielded even higher inhomogeneities which are believed to be due to local curvature of the lcm2 samples. The relaxation of GaAs/AlAs Braggreflectors of 3μm overall thickness depends on the density of threading dislocations i.e. of the type of substrate (LEC or HB). The inhomogeneous strain field of misfit dislocations in InGaAs/GaAs multilayer systems and their inhomogeneous distribution leads to deformations in epitaxial layers limiting the dimensions of coherently scattering domains. The resulting mosaic spread in the epitaxial layer systems has been obtained using triple crystal measurements. The experimentally determined mosaic spread has to be taken into account to simulate the the diffraction pattern more correctly.

We propose a new approach, growth on compliant substrates, to achieve extended pseudomorphic limits. The compliant substrate can be approximately achieved with a corner supported membrane structure. Both thermal equilibrium model and dynamic model considering strain relaxation are used to analyze the relations between the extended critical thickness and the substrate thickness. Preliminary experimental results of InGaAs grown on GaAs membranes seem to support the theories.

A 45 mm long In0.05 Ga0.95 As ternary bulk crystal with an extremely uniform composition has succeeded to be grown at a constant temperature by the liquid encapsulated Czochralski (LEC) method with a continuous supply of only GaAs to the pseudobinary InAs-GaAs growth melt. A double crucible which has both growth and source melt zones has been developed to improve the controllability of die supply of GaAs to the melt. These zones are separated by a cylindrical wall with a slit through which source elements are continuously supplied from die source melt zone to the growth melt zone. These results demonstrate mat large and uniform InGaAs bulk crystals can be grown using the constant temperature LEC method with a double crucible and with a continuous supply of only GaAs.

Single strained layers of GaAs grown on InP have been studied using different optical techniques. Absorption has been measured on these structure which are believed to be type II. The absorption is found to increase slowly close to the threshold and the spectral shape is very similar to photoluminescence excitation spectra. No sharp excitonic peaks were found. The absorption has been modelled using K.p-theory including strain and confinement. The agreement with experiments is good with respect to the shape of the spectra but differs a factor of three with respect to the magnitude of the absorption. The strain and composition of the samples have been measured by a combination of photoluminescence and Raman spectroscopy.

This work reports on the calculations of the electronic structure of GaAs/GaxIn1−x P strained layer quantum wells. The calculations are based on the multiband envelope function approach, considering the valence band offset value that has been recently proposed. The effect of strain due to the lattice-mismatch is studied. The calculated results are compared with the data obtained from photoreflectance measurements. Satisfactory agreement is obtained.

This paper describes an experimental analysis of strained InAs/AlSb ultrathin-layer superlattices (ULSs) grown by MBE. Interface bonds of InSb or AlAs were selectively made in the ULSs by controlling the beam supply sequence during growth. Structural analysis was performed for ULSs on both InAs and AlSb buffer layers using Raman scattering. This analysis revealed that each constituent in the ULSs was relaxed individually only when the AlAs interface bond was combined with the AlSb buffer layer. Other combinations of the interface bond and buffer layer, however, resulted in a free-standing superlattice structure. These experimental results are consistent with the interface dependence of electron mobility reported for InAs/AlSb single quantum well structures.

Linearly-graded buffer layers are used to achieve exciton resonances in InGaAs/GaAs at the 1.3 μm dispersion minimum of optical fibers. We investigate the effect of various gradients in the linearly-graded InGaAs buffer layer of a p-i-n structure designed as an optical modulator. Samples were grown by molecular beam epitaxy on GaAs substrates at 450°C. Each consisted of an n-type graded buffer region followed by thirty In0.5Ga0.5 As quantum wells with Alo.35Ga0.65As barriers, and 5000 Å of ρ-type InGaAs. Gradients of 7.5%, 15%, and 30% In/μm, or 0.5%, 1%, and 2% misfit/μm were used to grade the In concentration from 0% to 35%. Room temperature absorption measurements reveal well-defined zero-field excitonic features near 1.3 μm for all samples. The exciton resonance becomes sharper as the gradient decreases. Analyses of these samples by TEM and double crystal X-ray diffraction confirm the trend that a slower grading yields better quality material.

InxGa1−xP(x>0.27) grown on a GaP substrate has a large direct-bandgap, which is suitable for yellow light emission on a transparent substrate. Because of the large lattice mismatch, usually a thick (10–20 μm) graded buffer layer was required to reduce the threading dislocation density. In this work we report that a thin (1.2 μm for x≃0.35), linearly graded buffer layer can filter out dislocations effectively. The structures were grown by gas-source molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) intensity oscillations and X-ray double-crystal diffraction were used to control and determine the composition, respectively. Threading dislocations are well confined in the buffer layer, as shown under transmission electron microscopy. Dislocation loops injected into the substrate were observed, similar to those observed in the Six Ge1−x/Si system. X-ray analysis also shows that the 3% mismatched buffer layer is fully relaxed. This relaxed buffer layer then can serve as a substrate for further growth. Homojunction and heterojunction light emitting diodes were fabricated to demonstrate the material quality.

Elemental Vapor Transport Epitaxy (EVTE) is a novel technique for semiconductor manufacturing, which combines the advantages of Molecular Beam Epitaxy (MBE) and Vapor Phase Epitaxy (VPE). EVTE provides a high level of elemental flux control, scaling to large deposition areas, and elimination of elemental Ga source related oval defects. EVTE has been successfully applied to the deposition of III-V and II-VI thin films and heterostructures. Design considerations and evaluations of the novel EVTE elements: elemental flux regulating valve operating at temperatures >1250°C with demonstrated response times less than 1 second and elemental flux distribution manifold are presented. The calculated operational parameters for EVTE are in good agreement with the observed experimental results.

This paper reviews the present status of heterojunction bipolar transistor (HBT) technology based on GaAlAs/GaAs and InP/InGaAs materials, and discusses a variety of approaches for device improvement. Among the possibilities presented are novel structures to reduce base-collector capacitance, and novel materials to increase breakdown voltage and reduce base-emitter turn-on voltage.

High electron mobility transistors (HEMTs) based on the InAlAs/InGaAs heterostructure have been grown on InP by molecular beam epitaxy. At room temperature, typical sheet charge densities of 2.1–3.0×1012 cm−2 and Hall electron mobilities over 10000 cm2 /V-s are obtained. An electron mobility as high as 13000 cm2 /V-s is achieved with a pseudomorphic Iny Ga1−y As channel and a y value of 0.70.

HEMTs with a T- or Γ-shaped gate and with gate lengths ranging from 0.1–0.25 urn have been fabricated. A record low noise figure of 0.7 dB with an associated gain of 8.6 dB at 62 GHz has been achieved with 0.1 μm Γ-gate devices, while T-gate devices exhibit a minimum noise figure of 1.2 dB with 7.2 dB associated gain at 94 GHz. Separately, a record fmax value of 455 GHz was determined by extrapolating at -6 dB/octave from the measured gain of 13.6 dB at 95 GHz.

Power HEMTs using a double heterojunction structure exhibit a record peak power-added efficiency (P.A.E.) of 49% with 8.6 dB power gain and 0.30 W/mm power density measured at 60 GHz. When biased and tuned for maximum output power, our best 60 GHz output power density to date is 0.52 W/mm with 33% P.A.E. and 5.9 dB power gain using a single heterojunction HEMT scheme with pseudomorphic channel. A similar device also yields peak P.A.E. of 26% with 0.20 W/mm power density and 4.9 dB gain at 94 GHz. These results represent the highest P.A.E.S and power gains ever reported for any transistor at these frequencies.

We report a comparison of InAs/AlSb and In0.53Ga0.47As/AlAs resonant tunneling diodes (RTDs) for high speed switching applications. Theoretical simulations are performed for both heterostructure systems using a two band tunneling model, which includes the effects of strain and band bending. Experimental peak current densities are observed to agree well with the calculated values over the range 1×104 A/cm2 to 5× 105 A/cm2. In both types of structures, the maximum peak current density (directly related to switching speed) is determined by device heating. In this regard, InAs/AlSb RTDs are found to be slightly superior to In0.53Ga0.47As/AlAs RTDs due to the low contact and series resistances of InAs. However, higher peak-to-valley ratios and swing voltages are obtained in the In0.53Ga0.47As/AlAs devices up to their maximum attainable peak current density (3.1×105 A/cm2 in this study). Both heterostructure systems yield RTDs with estimated switching times near 1 ps.

High voltage GaAs Schottky rectifiers fabricated using vapor phase epitaxy have been observed to be an order of magnitude higher in switching speeds than silicon. Measured rectifier barrier heights deduced from the I-V and C-V plots were found to be in good agreement with previously reported values. Our experimental results show no correlation between the epilayer thickness and barrier height.