Semi-insulating, n-type or p-type wafers were irradiated (3MeV, 4.5K, 6 x 1018 to 3.6 x 1019/cm2). The irradiated samples were investigated by measuring changes in the lattice parameter and diffuse scattering intensity close to various Bragg reflections. These measurements directly revealed the structure of the interstitial. Two types of Frenkel defect could be distinguished, via their differing annealing behaviors at room temperature and 500K. The details of the scattering intensity distribution indicated that a predominant role was played by close Frenkel pairs, with a typical separation of about 1nm between vacancies and interstitials in the case of the low-temperature defects. The unusually large strain field, or relaxation volume, of about 2 atomic volumes also indicated that these defects arose from double displacements. The Frenkel pairs that annealed out at about 500K were characterized by a much smaller relaxation volume of about 1 atomic volume. Defect introduction rates of about 1/cm were deduced, and it was shown that total defect densities of 3 x 1019/cm3 could be achieved without any sign of saturation or defect clustering. The defect reactions during irradiation, as well as during annealing at up to 800K, were considered with regard to the trapping and de-trapping of mobile interstitials at other intrinsic defects, and the suppression of dislocation loop formation. No essential difference was observed between differently doped samples after high-dose irradiation.

A.Pillukat, K.Karsten, P.Ehrhart: Physical Review B, 1996, 53[12], 7823-35