High-pressure far-infrared magneto-optical and luminescence studies of electronic states of impurity donors-D(X) centres-in high purity GaAs

High-pressure studies of electronic states of impurity donors-D(X) centres-in high purity GaAs are reported. For the first time, the diamond anvil high-pressure cell technique has been applied to far-infrared (FIR) magneto-optical experiments. Absorption due to the 1s-2p⁺ transition for different shallow donor species is investigated in transmission experiments using far-infrared laser radiation at pressures up to 40 kbar. For pressures up to 20 kbar the photoconductivity technique with a standard Unipress optical cell is also used. A shallow-deep transition is observed for sulphur and silicon donors close to 25 and 30 kbar, respectively. The transition is similar to that for the Ge donor at 9 kbar reported previously. A deep state responsible for quenching of FIR absorption is further investigated in photoluminescence experiments. Large 'chemical shifts', anti-crossing effects and fast electron capture at low temperatures demonstrate the coexistence of strong localization, A₁ symmetry and the non-metastable (non-D(X) like) character of the observed deep donor states. The present investigation and earlier results with InSb demonstrate that three types of states-shallow and two types of deep states, D(X)-like and deep A₁-are generally expected to be formed by impurity donors which form D(X) centres.