Parameters influencing interfacial morphology in GaAs/Ge superlattices grown by metal organic chemical vapor deposition

We investigated the epitaxy and morphology of GaAs/Ge superlattices grown by metal organic chemical vapor deposition (MOCVD) under a range of conditions. The surfaces of Ge layers deposited on GaAs at 650 °C and 100 Torr are observed to be rough in cross-sectional transmission electron microscopy. When either the temperature is lowered to 500 °C or the pressure is increased to 250 Torr, the surface of the first deposited Ge layer is observed to be smooth. This behavior suggests that Ge roughening is a thermodynamically favorable process that can be kinetically limited with appropriate growth conditions. At 500 °C, GaAs islands on Ge do not completely coalesce into one film. This may result from poor surface coverage; the short depositions would not be sufficient to coarsen and completely coalesce the islands. At 650 °C, growth on offcut substrates did not suppress antiphase boundaries, likely due to the unique conditions for GaAs/Ge superlattice growth. A wide-range of two- and three- dimensional nanostructures are formed and should allow insight in structure-property correlations in semiconducting thermoelectric materials.