Abstract
P-ZnSe/GaAs heterojunctions, prepared by chemical vapour deposition (CVD) of ZnSe thin films on GaAs substrates at temperatures between 490 and 650°C, were characterized chemically and optically. Depth profiling of Ga and Se concentrations by secondary ion mass spectroscopy yielded the CVD-growth temperature dependent diffusion coefficients D( T) = D 0exp( E 0/ kT) with E 0 values of 3.4 eV and 1.7 eV for Ga in ZnSe and Se in GaAs, respectively. Growth temperatures of about 560°C during a period of 3 h led to an interface about 1000 Å thick with gradually mixed chemical composition, still small compared to the width of the space charge layer. Optical characterization by spectral ellipsometry confirmed the nearly abrupt ZnSe/GaAs interface of junctions prepared at 575°C. As demonstrated by the comparison to simulated spectra, a mixed (ZnSe-GaAs) interface is not thicker than 200 Å. Ellipsometric data at energies above the band gap of ZnSe indicated, however, the existence of a non-absorbing thin film surface layer due to the hygroscopic behaviour of ZnSe.
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