Buffer-dependent mobility and morphology of quantum wells

Abstract

We find that the mobility and morphology of InAs/(Al,Ga)Sb quantum wells grown by molecular beam epitaxy on lattice-mismatched GaAs depends strongly on the composition of the buffer layers. Using atomic force microscopy we show that GaSb buffers provide atomically flat interfaces on the scale of the electron Fermi wavelength for the quantum wells. In contrast, AlSb buffers generate a very rough interface on the same scale. Van der Pauw measurements show that this results in a greatly reduced low-temperature mobility for InAs quantum wells grown on AlSb buffers. We propose that the Ga adatoms tend to be more mobile than Al adatoms and therefore smooth out the roughness generated in the nucleation layer. Using a GaSb buffer layer, we have achieved new record mobilities in InAs quantum wells.