Photoluminescence of thermally treated n+ Si-doped and semi-insulating Cr-doped GaAs substrates

Photoluminescence measurements are used to investigate the nature of the surface layers formed on n⁺ Si-doped and semi-insulating Cr-doped GaAs substrates after heat-treatment at 780–830°C in H₂ or He flow. At 5.5 K the heat-treated n⁺ substrates exhibit a band near 1.44 eV while the semi-insulating substrates are characterized by a phonon assisted transition with the zero-phonon band at 1.41 eV. Both these bands are identified with donor-acceptor pair recombination. The ionization energy of both the donor and acceptor for the 1.44 eV band is estimated to be ～ 35–40 meV and it is suggested that the acceptor is Si_As. The identities of the donor in the 1.44 eV band as well as that of the centers responsible for the emission at 1.41 eV are unknown.