GROWTH AND CHARACTERIZATION OF GAAS/GASE/SI HETEROSTRUCTURES

We have grown and characterized epitaxial GaAs grown on layered structure GaSe on As-passivated Si(111) for the purpose of using layered structure GaSe as a lattice mismatch/thermal expansion mismatch buff er layer in the GaAs on Si system. Films were grown on nominally (111) oriented Si substrates by Molecular Beam Epitaxy (MBE) and characterized by in-situ Reflection High Energy Electron Diffraction (RHEED), as well as ex-situ plan-view and cross-sectional Transmission Electron Microscopy (TEM). After GaSe was epitaxially grown at 500-degrees-C on As-passivated Si(111) substrates, GaAs growth was carried out at 500-degrees-C: As grown GaAs films (300 angstrom) were highly twinned. In-situ annealing at 650-degrees-C for 10 minutes reduced the density of twins as observed by RHEED. In plan-view TEM, Moire fringes from both GaAs and GaSe are observed and showed conclusively that the GaAs grew epitaxially on the GaSe without contacting the Si substrate. Cross-sectional TEM showed the interface between the Si and GaSe was not smooth on the atomic scale. In spite of this, the GaSe becomes smooth within about 2 monolayers of growth and the GaAs/GaSe interface appeared to be very smooth. Despite the crystalline defects seen in cross section in the GaSe film, the GaAs film grows epitaxially.