Anwendung der Roentgenbeugung zur Analyse der strukturellen Eigenschaften von homo- und heteroepitaktischen Halbleiterschichten auf ZnSe-Basis

Abstract

An asymmetric relaxation was observed for the azimuth directions [110] and [1-10]. The dislocation density before and after heating was estimated from the diffuse scattering. Values of 3.3 *10^3 /cm and 13 *10^3 /cm were derived for the [110]-azimuth direction. The residual strain of single ZnSe layers on GaAs substrates due to work hardening was found to be 2.0 *10^(-4) in agreement with theoretical predictions. A critical layer thickness for work hardening of about 2.0 µm was derived. Comparing the thermal expansion of homo- and heteroepitaxially grown device relevant MgZnSSe layers showed nearly equal thermal expansion coefficients of both layer types. These measurements could be utilized to extrapolate the thermal expansion coefficient of MgSe in the zincblende structure. A value of 4.2 * 10^(-6) /K was derived for the temperature range from 300 K to 500 K. In the second part of the work, the influence of two different growth start procedures on the structural perfection of homoepitaxially grown ZnSe-based layers is discussed. A drastic increase in crystalline quality of the epitaxial layers resulted from various changes in growth procedure. The most important was the introduction of an {\em in situ} hydrogen plasma cleaning of the ZnSe substrates prior to the ZnSe growth. It provides a substrate surface free from contamination enabling to reduce the defect densities in the epitaxial layers by two orders of magnitude.