Lattice defects produced in nondegenerate (1-10 Q, cm) />-type germanium at 10°K by 1.0-MeV electrons cannot be detected electrically immediately following bombardment. Illumination by light having energy less than the band gap reveals the defects in the form of ionized donors. During ionization, the carrier concentration decreases as the sum of two exponentials, with time constants in the ratio «*6 to 1. Subsequent thermal-annealing investigations show two recovery stages in the temperature range 40 to 70°K. These stages appear to be intimately related to the time constants for decay during illumination, with the lowtemperature recovery associated with the fast component and the high-temperature recovery with the slow component. Both stages of recovery are independent of the type of impurity. Regardless of the extent of illumination, the electrical conductivity and the carrier concentration have essentially the same values they had prior to bombardment. When illuminated sufficiently long to ionize all the defects, the ionized donors become extremely susceptible to annihilation when the temperature is increased, and the situation after heating to 70 °K represents true annealing. Illumination for shorter times results in some un-ionized defects which do not anneal upon heating to 70°K. Isochronal heating to 150°K then causes a transformation of most of the unannealed defects into a configuration which the authors call a "two-state defect," the same defect observed following irradiation at 77°K. The transformed defects break up at about 200°K. Along with the higher-temperature effects, some impurity-dependent recovery stages are noted. A model to partially account for the results is briefly discussed. 790 T. M. FLANAGAN AND E. E. KLONTZ

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