Structural study of GaSb/AlSb strained-layer superlattice

Owing to the lattice mismatch between GaSb and AlSb, a superlattice consisting of alternating layers of these materials will be strained. We have carried out ion-channeling measurements by backscattering of 1.76-MeV He ions, and present an experimental procedure and a data-analysis technique to measure the difference in strain between the two individual layers of the superlattice. The data analysis is based on computer simulations of channeling, the accuracy of which is supported by the many fine details of the experiments reproduced in the simulations. X-ray rocking-curve analysis yielded detailed profiles of strains in directions perpendicular and parallel to the surface. The x-ray value for the strain present at an unirradiated spot on the crystal is in excellent agreement with the value calculated by elasticity theory. In the bombarded region, the values of strain are less than the value calculated by elasticity theory. It appears that bombardment by the He ions reduced the strain by 50% and created lateral inhomogeneities in the crystal structure

Stability of the Wurtzite Structure

An analysis of available data for 20 wurtzite compounds of the ANB8-N type shows that the stability as compared with zinc blende is closely connected with deviations of the c / a ratio from the ideal value of 1.633. A simple qualitative model is proposed to account for this feature. The variation in c / a is then correlated with the charge parameter ZC / ℏωp, where Z is the (effective) valence, C Phillips's electronegativity difference, and ℏωp the plasma energy of the free-valence-electron gas. The results indicate that c / a may be predicted with an uncertainty of 0.1%

OBSERVATION OF KOHN-TYPE ANOMALIES IN THE ELECTRON-PHONON INTERACTION ON THE FERMI SURFACE OF DEGENERATE SEMICONDUCTORS

L'effet acoustoélectrique a été observé pour des vecteurs d'onde acoustique comparable au vecteur d'onde de Fermi. Pour des échantillons de GaAs avec une distribution d'électrons dégénérée, on trouve une discontinuité dans l'amplification piézoélectrique acoustique quand | q | = 2 | kF |, où q est le vecteur d'onde acoustique et kF est le vecteur d'onde de Fermi. La raison en est que, dans un gaz d'électrons dégénérés, l'émission d'un phonon avec conservation de l'énergie et de l'impulsion est impossible si | q | ⩾ 2 kF. Ces effets ont été observés avec des fréquences acoustiques de 1-3 × 1011 Hz à l'aide de la diffusion inélastique de rayons X.Acoustoelectric effects for acoustic wavevectors comparable to the electron Fermi wavevector have been observed. For GaAs samples with degenerate electron distributions, we find a discontinuity in the piezoelectric acoustic amplification at | q | = 2 | kF |, where q is the acoustic wavevector and kF is the Fermi wavevector. This occurs because, in an electron gas obeying degenerate statistics, phonon emission with simultaneous conservation of energy and momentum between initial and final electron states is not possible for | q | ⩾ 2 kF. These effects were observed at acoustic frequencies of 1-3 × 1011 Hz using inelastic x-ray scattering

X-ray diffraction study of a one-dimensional GaAs–AlAs superlattice

Low- and high-angle X-ray diffraction patterns have been obtained from one-dimensional superlattice crystals prepared artificially by alternately depositing predetermined thicknesses of GaAs and AlAs, on the (001) face of a GaAs single-crystal by molecular-beam epitaxy. The positions and intensities of several superlattice reflections obtained along the 00l, 11l and 02l reciprocal lattice rows have been recorded. The structure of the superlattice can be approximated by a model which incorporates elastic strains in the unit cell due to the lattice mismatch between GaAs and AlAs. The number of Ga and Al layers in the superlattice unit cell can be accurately determined from the low-angle scattering data while the relative intensities of the high-angle superlattice reflections are a sensitive measure of the elastic strain present in the lattice. It is shown that the elastic strain agrees with the value computed theoretically on the assumption that the strain is not relieved by dislocations at the GaAs-AlAs interfaces