MORPHOLOGICAL STABILITY AND CRYSTAL-STRUCTURE OF CVD-GROWN ZINC SELENIDE

The evolution of micromorphologies has been studied for polycrystalline ZnSe layers grown by low pressure CVD processes in the systems: Zn-Se-H2-Ar (Se method) and Zn-H2Se-Ar (H2Se method). We have found differences in morphological features, apparently due to specific growth and nucleation mechanisms. In technological applications coarse or fine grained materials with homogeneous grain size distribution are often advantageous. Such materials have been successfully prepared under kinetically controlled growth conditions with continuous nucleation, i.e. in contrast to the H2Se method with deposition temperatures up to 800-degrees-C by the Se method only at T less-than-or-equal-to 600-degrees-C and higher supersaturations. In the system Zn-Se-H2-Ar the reaction rate constant is comparatively higher, and therefore the layer growth at higher temperatures is mainly diffusion-limited with boundary layer resistance. Correspondingly there is a tendency to morphological instabilities with normal grain growth and texture formation. Abnormal or secondary grain growth occurs as a result of recrystallisation during long-time CVD processes. Results of X-ray texture measurements are analysed in relation to different growth morphologies.