Electronic Raman spectra of shallow acceptors in semi-insulating GaAs

Abstract

We report the first well-resolved, sharp-line electronic Raman (ER) spectra of shallow acceptors in GaAs. The material-dependent circumstances of these observations are particularly interesting. The spectra, taken with cw, neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser radiation at ∼15 K, were observed only in undoped, semi-insulating bulk GaAs, grown by the liquid-encapsulated Czochralski technique. The residual, shallow acceptors present in such material are completely compensated by the double donor, mid-band-gap defects EL2. The latter, in their metastable form, provide the essential means whereby a nonequilibrium population of holes can be generated and maintained on the acceptors. This situation is exploited to obtain a detailed analysis of the ER spectra of the shallow acceptors in this technologically important material, including the identification of the residual acceptors (C and Zn), the estimates of their concentration (≪${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$), the testing of their adherence to the parity selection rule, and their response to internal strains and electric fields. A comparison of ER spectra is made with p-type, semiconducting bulk GaAs, where only broad, unresolved spectra are obtained, presumably because of much greater acceptor concentrations (${>10\mathrm{}}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$).