Formation of DX Centers by Heavy Si Doping in MBE-Grown AlxGa1-xAs with Low Al Content

The dependence of shallow donors and DX centers on Si doping concentration in Al x Ga1-x As layers grown by MBE has been investigated. In the shallow-to-DX transition region around x=0.2, the concentration ratio of DX centers to shallow donors was proved to have strong dependence on Si doping concentration. While few DX centers were observed in the samples with an Si concentration of about 1×1017 cm-3 DX centers became dominant above 1×1018 cm-3. These results can be explained by the effect of electron distribution between Γ-valley and DX center level.