A mobility study of the radiation induced order effect in gallium arsenide

N-type gallium arsenide doped with silicon was irradiated with reactor neutrons to 10/sup 12/, 3/spl times/10/sup 12/, 10/sup 13/, 3/spl times/10/sup 13/, 10/sup 14/, 3/spl times/10/sup 14/, 10/sup 15/, and 3/spl times/10/sup 15/ cm/sup -2/ (1 MeV equivalent fluence). The temperature dependence of the mobility was obtained after irradiation and annealing to 550/spl deg/C for 30 minutes. The maximum value of the mobility, /spl mu//sub max/, with respect to temperature was obtained as a function of fluence. For samples which have been irradiated and then annealed, /spl mu//sub max/ goes through a maximum at a fluence of 10/sup 13/ cm/sup -2/ and is 10% higher than in the unirradiated samples. At higher fluences, the mobility degrades. We attribute the increase in mobility at lower fluences to a radiation induced order effect. The disappearance of the deep level EL12 could be associated with this effect. At higher fluences where the mobility degrades, we observe by photoluminescence spectroscopy, the gallium vacancy, a point defect introduced by the irradiation, and the transfer of the silicon atom from the gallium site to the arsenic site. This suggests that growth of the gallium vacancy or the silicon at the arsenic site can be associated with mobility degradation.<>