Growth conditions to achieve mobility enhancement in Al x Ga 1−x As-GaAs heterojunctions by m.b.e.

Modulation doped Al0.25Ga0.75As-GaAs heterojunctions have been prepared by molecular beam epitaxy (m.b.e.). Al0.25Ga0.75As layers were doped with Si to a level of ∼ 3 × 1017 cm−3, whereas the GaAs layers were either unintentionally doped, doped lightly n-type with Sn, or doped lightly p-type with Be. Heterojunction structures having single and multiple periods have shown enhanced mobility only with the AlxGa1−xAs layer at the surface and the GaAs layer underlying. These results represent the first report that electrons spill over only into the underlying GaAs layer from the top AlxGa1−xAs layer.