DEFECT DENSITY IN ZNSE PSEUDOMORPHIC LAYERS GROWN BY MOLECULAR-BEAM EPITAXY ON TO VARIOUS GAAS BUFFER LAYERS

We have investigated the influence of both the GaAs surface stoichiome try and the nucleation procedure on the defect density in ZnSe pseudom orphic layer. We have shown that the use of migration enhanced epitaxy (MEE) at low temperature in the first steps of the growth decreases t he defect density by two orders of magnitude. For a ZnSe layer grown b y conventional MBE on a (2 x 4)-GaAs surface the etch pit density (EPD ) is equal to 5 x 10(6) cm(-2) but it reaches 5 x 10(4) cm(-2) when ME E is used at the beginning of the growth. The same behavior is reporte d for the growth on a c(4 x 4)-GaAs surface but the use of MEE decreas es only the density down to 4 x 10(5) cm(-2). Atomic force microscopy shows that the surface roughness and morphology are also improved. We have tried to incorporate a thin BeTe layer between the GaAs buffer an d the ZnSe layer. The ZnSe growth start is two-dimensional but the def ect density is only of 8 x 10(5) cm(-2). (C) 1998 Elsevier Science B.V . All rights reserved.