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The inclusion of metamorphic buffer layers (MBL) in the design of lattice-mismatched semiconductor heterostructures is important in enhancing reliability and performance of optical and electronic devices. These metamorphic buffer layers usually employ linear grading of composition, and materials including In_xGa_1-xAs and GaAs_1-yP_y have been used. Non-uniform and continuously graded profiles are beneficial for the design of partially-relaxed buffer layers because they reduce the threading dislocation density by allowing the distribution of the misfit dislocations throughout the metamorphic buffer layer, rather than concentrating them at the interface where substrate defects and tangling can pin dislocations or otherwise reduce their mobility as in the case of uniform compositional growth. In this work we considered heterostructures involving a linearly-graded (type A) or step-graded (type B) buffer layer grown on a GaAs (001) substrate. For each structure type we present minimum energy calculations and compare the cases of cation (Group III) and anion (Group V) grading. In addition, we studied the (i) average and surface in-plane strain and (ii) average misfit dislocation density for heterostructures with various thickness and compositional profile. Moreover, we show that differences in the elastic stiffness constants give rise to significantly different behavior in these two commonly-used buffer layer systems.

We have analyzed the strain resolution of x-ray rocking curve profiles from measurements of the peak position and peak width made with finite counting statistics. In this work, we have considered x-ray rocking curves which may be Gaussian or Lorentzian in character and have analyzed the influence of the effective number of counts, full-width-at-half-maximum (FWHM) and the Bragg angle on the resolution. Often experimental resolution values are estimated on the order of 10⁻⁵ whereas this work predicts more sensitive values (10⁻⁹) with smaller FWHM and larger effective counts and Bragg angles.

Analysis of the peak position and the linewidths of various infrared modes is performed at high (300–850 K) and low (1.5–300 K) temperatures using the experimental data from the literature for LiKSO₄ which exhibits a sequence of phase transitions. The temperature dependences of the frequency and the linewidth which are derived from the anharmonic self-energy are fitted to the observed peak positions and the linewidths of the S–O stretching modes (internal ${\nu }_3$ modes at 1135 cm${}^{-1}$ and at 1180 cm${}^{-1}$), peak position of the S–O bending ${\nu }_4$ (internal) modes, the peak position and the linewidth of the Li mode at 429 cm${}^{-1}$ (external mode), and of the infrared band at 363 cm${}^{-1}$ for LiKSO₄.

Our calculated peak positions and the linewidths, which are in good agreement with the observed data show that the anharmonic self-energy model describes adequately the observed behavior of the successive phase transitions in LiKSO₄.