PHONONS AND INTERNAL-STRESSES IN IV-IV AND III-V SEMICONDUCTORS - THE PLANAR BOND-CHARGE MODEL

We fit phonon-dispersion relations of IV-IV (Si, Ge, and alpha-Sn) and III-V (GaAs, AlSb, and GaSb) semiconductor crystals along [100] and [111] directions by means of a planar bond-charge model. Eigenvectors at the X and L high-symmetry points are predicted using the fitted parameters for the HI-V crystals. For GaAs, results agree fairly well with ab initio calculations and experimental data. Using the mass approximation we deduce the phonon-dispersion curves of AlAs from those of GaAs, finding good agreement with ab initio calculations. The phonon dispersions obtained from our measured Raman frequencies of confined modes in GaAs/AlAs superlattices also compare favorably with the performed calculations. Internal strain parameters for these zinc-blende structure crystals are determined from the fitted planar force constants and found to be in good agreement with ab initio calculations and the few available x-ray experimental results. General trends of the internal strain parameter as a function of metallicity and polarity are discussed.