Far-infrared dielectric function and phonon modes of spontaneously ordered

摘要

We present a far-infrared (fir) spectroscopic ellipsometry study of the phonon properties of partially CuPt_B-ordered (Al_xGa_(1-x))_(0.52)In_(0.48)P with x = 0, 0.32, 0.7 and 1.0, and degrees of ordering η from 0 to 0.63, as obtained by generalized ellipsometry measurement of the near-band-gap order birefringence. An anharmonic oscillator approach is used to model the ordinary and extraordinary dielectric functions and determine the infrared-active longitudinal and transverse phonon modes of the thin-film samples. Besides the isotropic GaP-, InP- and AlP-like phonon modes, we observe alloy-induced modes with low polarity. The phonon modes of highly ordered (Al_xGa_(1-x))_(0.52)In_(0.48)P with η～0.6 compared to phonon modes observed in the highly disordered quaternary solid solution. We propose measurement of the fir dielectric anisotropy as a sensitive indicator for existence of sublattice ordering in multicomponent group-Ⅲ-group-Ⅴ semiconductor alloys.