THE INFLUENCE OF SUBSTRATE SURFACE PREPARATION ON THE MICROSTRUCTURE OF CDTE GROWN ON (001) GAAS BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION

A cross-sectional transmission electron microscopy study has been performed on the microstructure of CdTe epitaxial buffer layers, which were grown upon 2-off (001) GaAs substrates by metalorganic chemical vapour deposition (MOCVD). The substrates were prebaked at various temperatures instead of the usual acid etching treatment. It was shown that single crystal films were only obtained for baking temperatures of 550 and 590-degrees-C. These single crystal deposits exhibited a distinctive anisotropic defect structure with subgrain boundaries and 90-degrees-type misfit dislocations perpendicular to the off-cut axis and stacking faults and a mixture of 60-degrees-type and 90-degrees-type misfit dislocations parallel to the off-cut axis. All of the stacking faults and 60-degrees-type dislocations lie on the plane (111) producing a 6-degrees rotation between the substrate and deposit lattices about the offcut axis. The development of this microstructure has been ascribed to the formation of high aspect ratio island nuclei and differences in Schmid factors due to the offcut. This microstructure was compared to that produced on an etched substrate and it appears that fine scale substrate surface roughness eliminates both of these influences.