ARSENIC PRECIPITATE ACCUMULATION AND DEPLETION ZONES AT ALGAAS/GAAS HETEROJUNCTIONS GROWN AT LOW SUBSTRATE-TEMPERATURE BY MOLECULAR-BEAM EPITAXY

AlxGa1-xAs/GaAs heterojunctions were grown by molecular beam epitaxy under normal growth conditions except that the substrate temperature was 250-degrees-C. After a 1 h anneal at 600-degrees-C, a narrow precipitate depletion (PD) zone was observed on the AlxGa1-xAs sides of the heterojunctions, while a high density precipitate accumulation (PA) zone was observed on the GaAs sides. The formation of these PD and PA zones is explained as a result of diffusion of excess As atoms across the interface from the AlxGa1-xAs layer to the GaAs layer. No significant difference in PD and PA zones was found at interfaces between AlxGa1-xAs grown on GaAs and GaAs grown on AlxGa1-xAs, indicating a negligible effect due to the growth sequence. Widths of PDs were about 250 angstrom, exhibiting a weak dependence on the Al concentration of the AlxGa1-xAs layers.