Neutron transmutation doping of high purity GaAs

High purity n-type GaAs samples grown by a variety of epitaxial techniques were transmutation doped with a low fluence of thermal neutrons to produce Ge and Se impurities from the host Ga and As atoms, respectively. Samples were chosen having low concentrations of Se and Ge donors and Ge acceptors prior to doping. Photothermal ionization and photoluminescence spectra as well as Hall effect data were recorded before and after doping and subsequent low temperature anneals. The high purity of these samples and low neutron dose, together with the low noise and high resolu-tion of the photothermal ionization measurements, has allowed the precise identification of the Se and Ge donor peaks through an accurate determination of their ls-2p(m=-l) transition energies. Comparison of the relative concentra-tions of shallow donors and acceptors, obtained from the photothermal ionization and photoluminescence spectra, with N_D and N_A determined from the Hall effect data, allowed the activation of Se and Ge to be measured. The observation of Ge_Ass acceptors after doping and of the incomplete activation of Se as donors are interpreted in terms of transmutation induced recoil of the Se and Ge due to γ-pray and e -v_e pair emission.