Shallow-deep instability of donor impurity states in Al-Ga-As system and its control by superlattice structure

Abstract

Donor-state instability in the Al-Ga-As system was investigated using selectively-doped short-period superlattices (< 40 Å). The local atomic configuration around an impurity and the band structure were independently controlled by changing the Al composition in the doping area and the layer thicknesses of the superlattices, respectively. The electrical properties were studied by DLTS and Hall measurements. The deep-level (DX-center) concentration in the superlattice increases with the increase in Al composition around the donor impurities under a constant band-gap condition. Under a constant local configuration, the DX-center concentration increases with the increase in the band-gap energy. The DX-center formation is effectively suppressed by AlAs/n-GaAs superlattice. A new DX-center formation model, taking into acount the local configuration effect, is discussed.