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 °C. After a 1 h anneal at 600 °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 Å, exhibiting a weak dependence on the Al concentration of the AlxGa1−xAs layers.