A photoluminescence study of the donor structure in Al_xGa_1-xAs

A photoluminescence study at low temperatures of Si-doped Al_xGa_1-xAs (0<x<0.6) reveals the existence of four donor levels D₁, D₂, D₃, D₄, in order of increasing ionisation depth. The number of donor levels and the dependence of their ionisation energies on the composition parameter x accords qualitatively with theoretical expectations. D₁ can be identified with the common 'shallow donor'. D₂ and D₃ have been reported in an earlier PL study by Dingle and co-workers (1977). The position of the D₄ level suggests an identification with the DX centre. Its luminescence properties have been the subject of a previous publication.