Irradiation was carried out at 15K, using an incident energy of 2MeV and a fluence of 1018/cm2. Annealing was carried out at temperatures ranging from 100 to 1000K. Differing annealing behaviors, of the Ga and P vacancies which were detected after electron irradiation, were observed. A recovery stage at temperatures of between 100 and 400K was attributed to the annealing of Ga vacancies, and a recovery at temperatures above 900K was attributed to the annealing of P vacancies. Hall measurements were used to determine the location of the Fermi level in the band-gap during annealing. Two different ionization levels of the P vacancy were found, and were attributed to the transitions: VP+/VPcirc and VPcirc/VP-.

A.Polity, T.Abgarjan, R.Krause-Rehberg: Applied Physics A, 1995, 60[6], 541-4