Molecular beam epitaxy of InAs quantum wells on InP(001) for high mobility two-dimensional electron gases

Abstract

InAs quantum wells are grown epitaxially as being embedded in (Ga,In)As–(Al,In)As double heterojunctions on InP(001). Despite an extensive gradual composition variation introduced in the buffer layer to overcome the mismatch of the lattices between InAs and InP, the layers relax during the epitaxy, as manifested by a cross-hatch pattern. The mobility of the two-dimensional (2D) electron gases in the quantum wells is nonetheless large, fairly unaffected by the presence of misfit dislocations generated in the lattice relaxation. The strain states in the epitaxial layer is analyzed using the X-ray diffraction. Transmission electron microscopy reveals that the relaxation is localized in the buffer layer, leaving the epitaxial growth in the quantum-well region coherent. The second subband of the 2D state is shown to be occupied when the sheet electron density is relatively low as the higher subbands are confined by the (In,Al)As layers.