CHARACTERIZATION OF ZNSE GAAS HETEROJUNCTIONS BY SIMS AND ELLIPSOMETRY/

P-ZnSe/GaAs heterojunctions, prepared by chemical vapour deposition (C VD) of ZnSe thin films on GaAs substrates at temperatures between 490 and 650-degrees-C, were characterized chemically and optically. Depth profiling of Ga and Se concentrations by secondary ion mass spectrosco py yielded the CVD-growth temperature dependent diffusion coefficients D(T) = D0 exp(E0/kT) with E0 values of 3.4 eV and 1.7 eV for Ga in Zn Se and Se in GaAs, respectively. Growth temperatures of about 560-degr ees-C during a period of 3 h led to an interface about 1000 angstrom t hick with gradually mixed chemical composition, still small compared t o the width of the space charge layer. Optical characterization by spe ctral ellipsometry confirmed the nearly abrupt ZnSe/GaAs interface of junctions prepared at 575-degrees-C. As demonstrated by the comparison to simulated spectra, a mixed (ZnSe-GaAs) interface is not thicker th an 200 angstrom. Ellipsometric data at energies above the band gap of ZnSe indicated, however, the existence of a non-absorbing thin film su rface layer due to the hygroscopic behaviour of ZnSe.