OPTICAL-IDENTIFICATION OF THE GALLIUM VACANCY IN NEUTRON-IRRADIATED GALLIUM-ARSENIDE

Gallium arsenide grown by the metallorganic-chemical-vapor-deposition method was irradiated at room temperature with fast neutrons in the fl uence range 10(12) to 3 X 10(15) cm-2 (1.00 MeV equivalent fluence in gallium arsenide). The effects of neutron irradiation were studied by photoluminescence (PL) spectroscopy in the energy range 0.5-1.55 eV. I n the samples irradiated to 3 X 10(13) cm-2 and higher fluences, we ob serve a transition at 1.4745+/-0.0003 eV in the PL spectrum recorded a t 2 K. Its intensity increases with neutron fluence. Upon increasing t he temperature at which the PL is recorded, the transition shifts to h igher energies, and an additional higher-energy component appears. At 20 K, the energy of the doublet is 1.4750 and 1.4786+/-0.0003 eV. The temperature dependence suggests that the low-energy component is a don or-acceptor pair and the high-energy one is a transition from the cond uction band to the acceptor. We identify the acceptor as the gallium v acancy (V(Ga)). We deduce its energy to be at 42.2+/-0.3 meV above the valence band. Replicas involving the 37-meV LO phonon were observed. Isochronal annealing was performed on samples irradiated to I X 10(13) and 3 X 10(13) cm-2. Samples which were irradiated and then annealed to 500 and 550-degrees-C exhibited the same doublet and their phonon r eplicas in the PL spectrum. This suggests that V(Ga) is dissociated at 500-degrees-C from a complex formed during neutron irradiation. The e ffect of neutron irradiation and of isochronal annealing on other tran sitions observed by PL is presented. These transitions include the sha rp transition at 0.702 eV, which has been associated with the arsenic antisite defect (As(Ga)), and the broad transition at approximately 1 eV. The modifications in the infrared PL spectrum are discussed in par allel with deep-level transient-spectroscopy data.