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Notes: Lattice-matched and strained InxGa1−xAs/In0.52Al0.48As single quantum wells with x=0.53 and x=0.60 have been studied by the optical modulation technique of photoreflectance (PR) at room temperature. The measurements have allowed the observation of interband transitions from the heavy- and light-hole valence subbands to the conduction subbands. The PR data have been adjusted with a least-squares fit to the first-derivative functional form. The energetic positions of the optical transitions deduced from the fit have been compared with theoretical values obtained by an envelope function model calculation including strain effects. The best adjustment allowed the determination of the conduction-band offset parameter Qc which is found equal to 0.71±0.07 for the lattice-matched and strained compositions.

Notes: Two-dimensional growth of GaAs on (100) silicon has been achieved by combining laser-assisted growth and modulation molecular-beam epitaxy techniques. The misfit dislocations were shown to form a regular cross-grid with satellite reflections characteristic of a two-dimensional homoepitaxial growth as also revealed by the perfection of the moiré patterns of the GaAs/Si interface. The few antiphase domains generated at the interface were observed to annihilate very fast. The top surface of GaAs was free of antiphase domains. Planar defects such as stacking faults and microtwins are also eliminated.

Notes: A systematic study of the growth of high-quality films of GaAs on Si substrates has been performed for applications in devices, particularly in optoelectronic devices for cointegration in optical interconnects. The effort for optimized active layers was approached through the separate optimization of substrate preparation, growth time parameters, and postgrowth treatment. In particular, the study of growth involved the investigation of the effect of silicon substrate orientation, post-growth treatment, as well as multilayer and, especially, silicon buffer layers. For quantification of film quality, a number of characterization methods were used both in situ: reflected high-energy electron diffraction (RHEED); and ex situ: optical, electrical [current versus voltage (I-V), capacitance versus voltage (C-V), deep-level transient spectroscopy (DLTS), Hall], transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron channeling patterns, x-ray double-crystal diffractometry (DDX). Schottky diodes, p-n heterojunctions, and metal-semiconductor-metal photoconductors/photodetectors (MSM PC/PDs), field-effect transistors, and high electron mobility transistors were fabricated on these films. The most crucial parameter for device operation and film uniformity is the complete absence of antiphase boundaries which increase leakage, degrade mobilities, and seem to result in interface two-dimensional electron gas in substrates misoriented toward 〈110〉.Absolutely smooth GaAs morphology is obtained using a molecular-beam epitaxy grown Si buffer layer and controlling the orientation of the GaAs film so that the [110] direction is parallel to the 〈110〉 misorientation direction of the vicinal (001) substrates. This can be ensured by an As4 prelayer grown at 350 °C. A double 2×1 domain Si surface seems to be preferable, as it allows the choice of such a GaAs orientation. GaAs growth is then 2D from the very early stages of growth, following the homogeneous nucleation of 3D GaAs islands, resulting in the complete elimination of planar faults. A perfectly regular displacement-type moiré pattern in the GaAs/Si interface is then observed. GaAs buffers on Si with an MBE Si buffer exhibit high resistivity, probably due to growth on contamination-free surfaces. The lowest ever reported 1 μm DDX full width at half-maximum of 255 arcsec was observed for such a GaAs/Si/Si layer. Nevertheless, accurate TEM dislocation counts indicate a dislocation density in the low 108 cm−2 range. In addition, a saturation in DDX FWHM values appears for an epilayer thickness of about 2 μm. This may be related to values being limited by wafer bowing or it may indeed reflect a limit in film quality. Post-growth rapid thermal annealing results in redistribution of dislocations in a nonuniform way with most congregating in small areas of high dislocation density, leaving large areas with low dislocation density.It is concluded that by either increasing the GaAs epilayer thickness or the sample temperature one produces a residual compressive stress that forces the threading dislocations to slip, thus reducing their density by reactions that become moreprobable with proximity. The residual dislocation density of about 108 cm−2 is attributed partly to threading dislocation generation during the early stages of epitaxy and only partly to generation from tensile thermal stress during cooling. Schottky diodes on GaAs/Si break down at the same or similar voltages as on homoepitaxial material. MSM PC/PDs have comparable dark dc leakage currents, somewhat lower dc photoresponse, and comparable rise and fall times, and metal-semiconductor field-effect transistors (1.5 μm gate length) fabricated on GaAs/Si/Si show a maximum extrinsic transconductance of 230 mS/mm, actually somewhat higher than for homoepitaxial devices. Thus, device results allow us to claim that we have achieved a technology that leads to heteroepitaxial GaAs/Si films which compare in performance to homoepitaxial GaAs/GaAs within about 10% for applications in most devices. The use of an MBE Si buffer layer, in addition to improving the quality of the GaAs layer, results in a reduction of a processing temperature by at least 100 °C. This reduction, along with the elimination of the step-doubling processing step, makes GaAs film growth compatible to unmetallized fully processed complementary metal-oxide-semiconductor (CMOS) Si wafers.

Notes: The valence-band splitting due to strain in molecular-beam epitaxially grown GaAs on Si has been observed by photoreflectance. The strain has been obtained from the valence-band splitting and was found to be in agreement with results obtained by x-ray rocking curve measurements, photoluminescence, and Raman spectroscopy. The temperature dependence of the strain has also been measured and found to be in agreement with thermal expansion effects.

Notes: The two-dimensional electron gas (2DEG) distribution and conduction-band profile tailoring of the AlxGa1−xN/GaN/AlyGa1−yN/GaN double heterostructure (DH) has been studied in detail by self-consistent Poisson–Schrödinger (SCPS) calculations. We show that a 2DEG is always created at the AlyGa1−yN/GaN interface beyond the GaN quantum well but the latter will not be occupied if the lower barrier thickness or Al content exceed those of the top barrier. These findings were confirmed by capacitance–voltage profiling of a 5 nm Al0.3Ga0.7N/5 nm GaN/AlyGa1−yN/GaN DH grown by molecular beam epitaxy on n+ GaN, where the lower barrier thickness was varied between 10 and 40 nm. A maximum 2DEG density of 1.0×1013 cm−2 was achieved for a 40 nm lower barrier and y=0.2. We found good agreement between the integrated carrier concentration versus depth curve and the calculated equilibrium 2DEG density. The bias required to bring about a flatband condition at the lower AlyGa1−yN/GaN interface increased with the thickness of the lower barrier up to −9 V for 40 nm and y=0.2, in agreement with SCPS calculations of the subband depletion under negative bias. We discuss the potential use of an AlGaN/GaN DH with a thick GaN well for the realization of a 2DEG isolated from the buffer by strong barrier enhancement. © 2002 American Institute of Physics.

Notes: The effects of the channel electron density on the interband optical transitions of strained (x=0.6 and 0.65) and lattice-matched (x=0.53) InxGa1−xAs/In0.52Al0.48As/InP high-electron-mobility transistor structures have been investigated by phototransmittance at room temperature. Analysis of the ground and first excited transitions for low and high densities, respectively, enabled a separate estimation of the electron densities occupying each one of the first two subbands. It was found necessary to include the modulation of the phase-space filling in the analysis of the spectra, especially for the samples with a high electron density, in which case this modulation mechanism becomes dominant. © 1996 American Institute of Physics.

Notes: Electrical transport in a modulation doped heterostructure of In0.53Ga0.47As/In0.52Al0.48As grown on Si by molecular beam epitaxy has been measured. Quantum Hall effect and Subnikov–De Haas oscillations were observed indicating the two-dimensional character of electron transport. A mobility of 20 000 cm2/V s was measured at 6 K for an electron sheet concentration of 1.7×1012 cm−2. Transmission electron microscopy observations indicated a significant surface roughness and high defect density of the InGaAs/InAlAs layers to be present due to the growth on silicon. In addition, fine-scale composition modulation present in the In0.53Ga0.47As/In0.52Al0.48As may further limit transport properties.

Notes: The effectiveness of In0.10Ga0.90As/GaAs strained-layer superlattices (SLSs) as barriers for the threading dislocation propagation, in molecular-beam-epitaxy GaAs-on-Si structures with Si buffer layers, has been investigated. It is shown that the interaction of threading dislocations with the strain field of SLSs is effective in limiting their propagation. The interaction is stronger as the total thickness of In0.10Ga0.90As (i.e., SLS periods) is increased. SLSs with thinner individual layers resulted in a lower dislocation density and a better structural quality at the GaAs/Si interface. © 1994 American Institute of Physics.

Notes: The appearance of quantum wirelike morphology on InGaAs single quantum well structures grown by molecular beam epitaxy on (100)InP vicinal surfaces is reported. The results of transmission electron microscopy reveal that the misorientation of the substrate drives the development of a lateral contrast modulation related to In-rich or Al-rich regions oriented along {133} or {122} planes that initiate on the InAlAs tensile buffer layer and propagate across the structure, giving rise to an anisotropic rippling of the InGaAs well. Conversely, a misfit dislocation network at the InAlAs/InP interface was observed for the same layers grown on exact (100) surface. A comparison of the two structures suggest that the development of such modulated configuration is apparently a strain relieving mechanism. © 1995 American Institute of Physics.

Notes: The structure of In0.52Al0.48As films grown on InP (100) by molecular beam epitaxy, at growth temperatures in the range of 530–590 °C, are analyzed by transmission electron microscopy. The existence of contrast inhomogeneities along the 〈010〉 fcc soft directions, the appearance of which depends on the temperature and the distance to the substrate, is reported. It is shown that these contrast irregularities in InAlAs are related directly to the existence of precipitates in the InAlAs/InP interface, whose origin can be found in the formation of an InAs layer under an As-stabilized InP surface.