We have grown and characterized epitaxial GaAs grown on layered struct
ure GaSe on As-passivated Si(111) for the purpose of using layered str
ucture GaSe as a lattice mismatch/thermal expansion mismatch buff er l
ayer in the GaAs on Si system. Films were grown on nominally (111) ori
ented Si substrates by Molecular Beam Epitaxy (MBE) and characterized
by in-situ Reflection High Energy Electron Diffraction (RHEED), as wel
l as ex-situ plan-view and cross-sectional Transmission Electron Micro
scopy (TEM). After GaSe was epitaxially grown at 500-degrees-C on As-p
assivated Si(111) substrates, GaAs growth was carried out at 500-degre
es-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 epita
xially on the GaSe without contacting the Si substrate. Cross-sectiona
l TEM showed the interface between the Si and GaSe was not smooth on t
he atomic scale. In spite of this, the GaSe becomes smooth within abou
t 2 monolayers of growth and the GaAs/GaSe interface appeared to be ve
ry smooth. Despite the crystalline defects seen in cross section in th
e GaSe film, the GaAs film grows epitaxially.