OPTICAL-PROPERTIES OF ZINCBLENDE CDSE AND ZN(X)CD(1-X)SE FILMS GROWN ON GAAS

We present room-temperature ellipsometric measurements of the dielectric function of ZnxCd1-xSe single-crystal films grown on (001)GaAs in the 1.5-6.0-eV energy region x ranging from 0 to 1. We identify the E0, E0 + DELTA0 E1, E1 + DELTA1, and E2 threshold energies using the CdSe band structure calculated with a nonlocal empirical pseudopotential method. We find that the contact exciton effect has to be included in the calculated dielectric function of CdSe in order to obtain good agreement with our measurements. A compositon-dependent critical-point analysis of the E1 and E1 + DELTA1 structures has been performed. We also find that the spin-orbit-splitting band gap DELTA1(x), the linewidths, and the excitonic angles are about maximum at x = 0.5, which we attribute to the statistical fluctuation of the alloy composition. Finally, the E1 and E1 + DELTA1 critical-point amplitudes cannot be understood by the one-electron approximation, confirming the existence of strong excitonic effects.