DX STATES IN GAAS/ALAS SHORT-PERIOD SUPERLATTICES DOPED SELECTIVELY WITH SILICON

We investigate the electrical properties of up to 12 GaAs/AlAs superlattices doped uniformly or selectively with silicon. We determine for each sample the apparent energy of the DX silicon donor by performing Hall-effect measurements. We find this energy depends on the discrete values of the energy assigned to the deep donor states present in GaAs, AlAs and interface layers respectively. Interdiffusion of silicon in the adjacent layers occurred in selectively doped samples. This interdiffusion eff ect appears to be responsible for shoulders in the thermal annealing of persistent photoconductivity. We determine the energies of both DX states with an all-Ga and all-Al environment of the silicon donor. They differ by more than 55 meV. Finally we give Hall and photo-Hall data under hydrostatic pressure which we interpret by taking into account the crossing of the LAMBDA conduction miniband over the X pseudo-direct miniband of the superlattice with applied pressure.