Growth and Characterization of Gase and GaAs/GaSe Hetero-Structures on As-Passivated Si Substrates

Abstract

We have grown and characterized layered structure GaSe on As-passivated Si( 111 ) and GaAs on GaSe on As-passivated Si(111) for the ultimate purpose of using layered structure GaSe as a lattice/thermal-expansion mismatch buffer layer for epitaxial GaAs on Si. Films were grown on (111) Si substrates by MBE and characterized by in-situ RHEED, ex-situ SEM, and both plan-view and cross-sectional TEM. GaSe grew epitaxially on As-passivated Si(111) substrates at 500°C with Se/Ga BEP (Beam Equivalent Pressure) ratios of 10-20. Small droplets were observed on the surface after GaSe growth, and are thought to be droplets of unreacted Ga. The density and size of the droplets decrease with increasing Se/Ga BEP ratio. When the GaSe surface was exposed to As, the droplets became GaAs islands. Subsequent GaAs growth was carried out at 400°C and 500°C, giving the following results for 300A thick films: As grown GaAs films were highly twinned, and some polycrystalline GaAs was present in the film grown at 400°C. In-situ annealing at 650°C for 10 minutes reduced the density of twins in both cases. The morphology of the GaAs films are that of an interconnected network of islands, with a feature size of about 500Â and 1000A for the film grown at 400°C and 500°C, respectively. 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.