High electron mobility in InSb epilayers and quantum wells grown with AlSb nucleation on Ge-on-insulator substrates

InSb epilayers and InSb/Al0.20In0.80Sb quantum wells (QWs) were grown on 4°-off-axis Ge-on-insulator (GeOI) substrates by molecular beam epitaxy. An initial AlSb nucleation was found to be important for achieving good crystalline quality. For a 4.0-μm-thick InSb epilayer and 25-nm-thick InSb QW, the room-temperature (RT) electron mobility was increased by 25% and 60% [58 000 cm2/(V-s) for the epilayer and 24 000 cm2/(V-s) for the QW], respectively, by using an off-axis GeOI substrate instead of an on-axis GeOI (001) substrate. This significant improvement may be attributed to the reduction of antiphase domains, microtwins, and threading dislocations. A modified QW structure on a 4°-off-axis GeOI substrate showed a further 25% improvement in RT electron mobility with a value 32 000 cm2/(V-s). This is the highest RT electron mobility in an InSb QW grown on a Ge-based substrate to date.