The composition of a series of AlxGa1−xAs layers grown epitaxially by molecular beam epitaxy (MBE) on GaAs has been measured independently by double axis x-ray diffractometry and reflection high-energy electron diffraction. From a quadratic fit to the data, we deduce the lattice parameter mismatch between AlAs and GaAs and the Poisson ratio of AlAs. Asymmetric reflection rocking curves and synchrotron x-ray topography have been used to show that the anomalously low substrate-layer peak splitting for the 1-μm-thick AlAs layer results from relaxation, which is asymmetric. Use of the AlAs rocking curve peak splitting corrected for relaxation yields a mismatch of 1600 ppm (±1%) between AlAs and GaAs, and 0.28±0.01 for the Poisson ratio of AlAs.

Impact of quantum well intermixing on polarization anisotropy of InGaAs/InGaAsP quantum well modulatorsThis letter describes the performance of electro-absorption optical modulator structures, based on strain-balanced InGaAs/AlGaAs p-i-n multiple quantum wells ͑MQWs͒. It specifically considers the influence of lattice mismatch with the graded InGaAlAs buffer arising from unrelaxed material forming the substrate upon which the p-i-n structure is grown. We have shown that to achieve a lattice constant corresponding to the average for the MQW region, it is necessary to grade the buffer up to a higher indium concentration than the average indium concentration of the MQW. We have found that mismatched samples exhibit poorer modulation on the long wavelength side of the exciton peak as a result of a greater reduction in the exciton peak with applied field, and we attribute this to screening and nonuniform fields resulting from the ionization of defects at high fields. We have also shown that the similar effect induced by going to lower barrier potentials is relatively less important.

Magnetotransport measurements are reported for In0.53Ga0.47As layers grown by molecular beam epitaxy (MBE) at different substrate temperatures (Ts) and either δ- or slab-doped with Si. Multiple subband densities deduced from the Fourier analysis of 1.2 K Shubnikov–de Haas measurements are compared with those derived from self-consistent calculations which include nonparabolicity and the doping profile width wSi as a fitting parameter. Significant spreading of the Si donors away from the doping plane is deduced for deposition at Ts≊520 °C, while no measurable migration is inferred for Ts≤470 °C, leading to near-ideal δ-doping behavior. Contrary to previous results [McElhinney et al., J. Cryst. Growth 150, 266 (1995)], no evidence for amphoteric behavior has been found for Si areal densities up to 4×1012 cm−2.

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