A MICROSTRUCTURAL STUDY OF CRYSTALLINE DEFECTS IN PBSE/BAF2/CAF2 ON (111)SI GROWN BY MOLECULAR-BEAM EPITAXY

Epitaxial narrow gap lead selenide layers were grown on (111) Si substrates with the aid of an intermediate epitaxial BaF2/CaF2 buffer by molecular beam epitaxy. A microstructural study of the defects present in the different layers is provided mainly by transmission electron microscopy (TEM) and metallographic analysis. Moire pattern images have been used to investigate the residual strain in the CaF2 layer as a function of thickness, and a relaxation mechanism is proposed. The growth mode of CaF2 on (111) Si appears to be pseudomorphic with a critical thickness around 20 angstrom. The reduction of defects in the PbSe layer is clearly dependent on the crystalline quality and thickness of the fluoride layers. The PbSe layers obtained are monocrystalline with typical dislocation densities observed near the surface of a 2 mum thick PbSe layer below 10(7) cm-2.