OPTICAL STUDY OF (ALXGA1-X)0.5IN0.5P/GAAS SEMICONDUCTOR ALLOYS BY SPECTROSCOPIC ELLIPSOMETRY

The critical points of (AlxGa1-x)0.5In0.5P semiconductor alloys grown by metal-organic chemical vapor deposition and lattice matched to GaAs have been measured at room temperature in the 1.5-6.2 eV spectral region using spectroscopic ellipsometry. We have performed standard lineshape analysis of the second derivatives of pseudodielectric function data to obtain the standard critical point parameters (peak position, broadening parameter, amplitude, and excitonic phase angle) as a function of x. The properties of the E1 and the E1 + DELTA1 spectral structures have been observed for the first time. The anomalously small amplitude of the contribution of E1 + DELTA1 spectral feature relative to that of E1 is attributed to the k-linear interaction between the LAMBDA4,5v and LAMBDA6v valence bands, which is large in III-P alloys due to the very small spin-orbit splitting. The bowing parameter of DELTA1 is determined and discussed. The critical point parameters smoothly interpolate between those of the two ternary endpoints, Ga0.5In0.5P and Al0.5In0.5P. These parameters are discussed and compared with those of AlxGa1-xAs, (AlxGa1-x)0.5In0.5As/InP, and InxGa1-xAsyP1-y/InP.