GROWTH AND CHARACTERIZATION OF GASE AND GAAS/GASE ON AS-PASSIVATED SI(111) SUBSTRATES

We have grown and characterized epitaxial layered structure GaSe on As-passivated Si (111) and GaAs on GaSe on As-passivated Si (111) for the ultimate purpose of using the layered structure GaSe as a lattice mismatch/thermal expansion mismatch buffer layer in the GaAs on Si system. Films were grown on nominally (111) oriented Si substrates, by molecular beam epitaxy and characterized by in situ reflection high energy electron diffraction, as well as by ex situ scanning electron microscopy and both plan-view and cross-sectional TEM (transmission electron microscopy). In this study, GaSe was grown epitaxially on As-passivated Si (111) substrates at 500-degrees-C with Se/Ga BEP (beam equivalent pressure) ratios of approximately 10 and approximately 20. Small droplets were observed on the surface after GaSe growth. These are thought to be droplets of unreacted Ga. The density and size of the droplets decreases with the increasing Se/Ga BEP ratio. When the GaSe surface is exposed to As, the droplets become GaAs islands. Subsequent-GaAs growth was carried out at 400 and 500-degrees-C, giving the following results for 300-angstrom-thick films: as grown GaAs films were highly twinned, and some polycrystalline GaAs was present in the film grown at 400-degrees-C. In situ annealing at 650-degrees-C for 10 min reduced the density of twins in both cases. In plan-view TEM, Moire fringes from both GaAs and GaSe are observed and show conclusively that the GaAs grew epitaxially on the GaSe without contacting the Si substrate. Cross-sectional TEM shows the interface between the Si and GaSe is not smooth on the atomic scale. In spite of this, the GaSe becomes smooth with about 2 monolayers of growth and the GaAs/GaSe interface appears to be very smooth.