SCANNING FORCE MICROSCOPY STUDIES OF GAAS FILMS GROWN ON OFFCUT GE SUBSTRATES

The surface morphology of GaAs films grown on offcut Ge substrates is studied using a scanning force microscope (SFM). We investigated the e ffects of the Ge buffer layer, growth temperature, film thickness, and prelayer on the GaAs surface morphology. The starting Ge substrates a re offcut 6 degrees toward the [110] direction to minimize single step s on the substrates before molecular beam epitaxial film growth. We fi nd that comparing with GaAs samples grown without Ge buffer layers or with unannealed Ge buffer layers, samples with annealed Ge buffer laye rs are much smoother and contain no antiphase boundaries (APBs) on the surface. For thick (greater than or equal to mu m) GaAs films with an annealed Ge buffer layer, the surfaces display crosshatch lines and e longated mounds (along [(1) over bar 10],which are associated with the substrate offcut direction. As the film thickness increases, the cros shatch lines become shorter, denser and rougher, and the mounds grow b igger tan indication of GaAs homoepitaxial growth). We conclude that a nnealed Ge buffer layers are crucial for growing high quality GaAs fil ms with few APBs generated during the growth. In addition, under optim al conditions, different prelayers make little difference for thick Ga As films with annealed Ge buffer layers.