Composition dependence of optical phonon properties and dielectric functions of group-III arsenide ternary and quaternary mixed crystals

Optical properties of group-III arsenide ternary and quaternary alloys are investigated theoretically by a generalized mixed crystal theory. On the basis of a modified random element isodisplacement approach, long-wavelength optical phonon energies, phonon mode strengths and dielectric, functions of Al(x)Gal(1-x)As, AlxIn1-xAs, and GaxIn1-xAs ternary alloys, and also of AlxGayIn1-x-yAs quaternary alloys are calculated numerically in the whole compositional range. The results are discussed and compared with experimental results. It is confirmed that the optical phonon spectra of AlxGayIn1-x-yAs alloys will exhibit three optical phonon modes in most of the compositional range. (C) 2003 American Institute of Physics.