Lang Topographic Studies of III-V Heteroepitaxial Films Grown on Sapphire and Spinel

Abstract

Single-crystal layers of GaAs and GaP grown by chemical vapor deposition on sapphire and magnesium aluminate spinel substrates have been characterized by Lang x-ray topography and x-ray diffraction methods. Separate topographs and diffraction peak profiles of the substrate and layer were obtained without removing the layer from the substrate. Epitaxial layers grown on substrates prepared by different growth techniques were examined and compared. Layers shown to be monocrystalline by back-reflection Laue methods were revealed by Lang topography to be composed of small grains which were misoriented ±0.1° from the nominal orientation of the layer. Polishing scratches and growth striae in the substrates were found to influence the perfection of the layer. The Lang camera was used as a diffractometer to measure the misorientation of the layers from exact parallel epitaxy and to determine the radius of curvature of warped substrates.