Substrate lattice constant effect on the miscibility gap of MBE grown InAsSb

Abstract

The miscibility gap of molecular beam epitaxial grown InAs 1− x Sb x layers on GaAs (0 0 1) substrates is investigated using X-ray diffraction techniques and scanning electron microscopy. Four different buffer layers, GaAs, InAs, GaSb, and homogeneous InAs 0.5Sb 0.5 grown at 470°C, are used to investigate the strain effect on phase separation. The nominal composition of InAs 1− x Sb x is adjusted to x=0.5. The layers grown at relatively low temperatures show two different alloy compositions and consist of alternating plates approximately parallel to the substrate surface, both indicating the occurrence of phase separation. The critical temperatures are 415°C for the alloys grown on the GaAs and on the homogeneous InAs 0.5Sb 0.5 buffer layers and 435°C for the alloys grown on the InAs and on the GaSb buffer layers. They are much higher than the temperature predicted by the delta lattice parameter model (303°C). We believe that 415°C is the critical temperature which is purely determined by the excess entropy and enthalpy with no respect to the substrates. The use of substrates such as InAs and GaSb, whose lattice constants are close to those of the phase separated alloys, promotes the phase separation due to the strain effect.