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

We present room-temperature ellipsometric measurements of the dielectr ic function of ZnxCd1-xSe single-crystal films grown on (001)GaAs in t he 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 m ethod. We find that the contact exciton effect has to be included in t he calculated dielectric function of CdSe in order to obtain good agre ement with our measurements. A compositon-dependent critical-point ana lysis 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 attr ibute to the statistical fluctuation of the alloy composition. Finally , the E1 and E1 + DELTA1 critical-point amplitudes cannot be understoo d by the one-electron approximation, confirming the existence of stron g excitonic effects.