The influence of substrate on the self-organised island nucleation and morphology of metalorganic chemical vapour deposited GaSb

Metalorganic chemical vapour deposition was used to compare initial growth and film evolution of GaSb on GaAs, Ge, InAs and GaSb under identical conditions. These substrate-layer pairs allow the effects of lattice mismatch and chemical compatibility to be differentiated. GaSb forms self-organised islands on GaAs and Ge, where mismatches are each about 8%, but not on closely lattice matched InAs and GaSb. Substantial differences were observed, however, between islands grown on Ge and GaAs, the former yielding fewer but larger islands than the latter. For example growth for 30 s under optimised conditions gave typical island lateral dimensions of 150 nm with heights around 35 nm on GaAs, but respective values of 250 nm and 70 nm on Ge. The volumetric growth rates suggest that nucleation in the GaSb/Ge system is slower than previously reported island growth rates in the GaSb/GaAs system. Thicker layers grown on GaAs, GaSb and InAs show similar elongated pyramidal surface features with clearly visible facets, whereas growth on Ge results in a much smoother but irregular surface. Both of these characteristics are attributed to a closer chemical similarity in GaSb/GaAs than in the GaSb/Ge system.