Photoionization threshold of the deep donor in Si-dopedAlxGa1−xAs

In order to clear up the controversy about the magnitude of the lattice relaxation of the deep donor in $n$-type ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$, samples were exchanged between Philips and IBM. The present photocapacity study on an IBM sample definitely shows the existence of two photoionization processes: one with a threshold between 200 and 300 meV, representing an effective-mass-type deep donor with small lattice relaxation, and another one with a threshold near 700 meV, representing the so-called $\mathrm{DX}$ center with large lattice relaxation. These results suggest either two distinct donor configurations or a bistable character of the deep donor.