THE ROLE OF THE INITIAL NUCLEATION STAGE IN MICROSTRUCTURAL DEVELOPMENT FOR CDTE GROWN ON HEAT-CLEANED 2-DEGREES-OFF (001)GAAS BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION

A transmission electron microscopy (TEM) study of the initial nucleati on layers for the two-step growth of CdTe on 2 degrees-off (001) GaAs substrates by metalorganic chemical vapour deposition (MOCVD) is prese nted. For substrates which are degreased and etched in the usual manne r, the initial deposits are oriented with their axes parallel to those of the substrates and the defects are distributed isotropically. Init ial deposits grown on substrates which are prepared by thermal etching at 545-585 degrees C, however, contain both (001)- and (111)-oriented grains. When these polycrystalline initial deposits are heated to the ''bulk'' growth temperature, epitaxial regrowth occurs giving a singl e crystal film with a very distinctive anisotropic defect microstructu re with stacking faults and a mixture of 60 degrees-type and 90 degree s-type misfit dislocations parallel to the off-cut axis and subgrain b oundaries and 90 degrees-type misfit dislocations in the orthogonal di rection. All of the 60 degrees-type misfit dislocations and most of th e stacking faults lie on the plane (111) producing a rotation of 5-8 d egrees between the substrate and deposit lattices about the off-cut ax is. These effects are explained in terms of differences in resolved sh ear stresses as secondary defects are introduced during the regrowth p rocess.