Low-temperature recovery of irradiation defects inn-type germanium

Defect concentrations introduced into lightly doped $n$-type germanium by 1.0-MeV electrons at 7 °K have been monitored by measuring the hot carrier conductivity at 4.2 °K during a 0.66-μsec pulsed electric field of 100 V/cm and 1-sec duty cycle. Approximately 85% of the damage produced at 7 °K recovers in a thermal-annealing stage at 65 °K. Isochronal- and pulse-isothermal-annealing experiments, performed simultaneously on pairs of samples doped with approximately equal concentrations of different group-V impurities, show that the 65 °K annealing rate is dependent on the type of impurity. Radiation annealing was also studied by irradiating pairs of samples, damaged previously at 1.0 MeV, with low-energy electrons which produce little additional damage. The defects, which thermally anneal at 65 °K, radiation anneal at 7 °K with an annealing rate which is dependent on the type of group-V impurity dopant. This experiment suggests that one of the defects involved in these annealing processes is free to migrate over large distances near liquid-helium temperature. A model for the 65 °K stage is proposed in which the annealing is initiated by the breakup of an interstitial group-V impurity complex which was formed during 1.0-MeV irradiation. The interstitial is treated as a freely migrating particle which, when freed from the complex, can either migrate to a vacancy or be retrapped at an unoccupied impurity depending upon the relative charge states of these defects. From this model, it is possible to calculate the annealing rate of the 65 °K stage, the 7 °K-radiation-annealing rate, and the optical-annealing rates for optically stimulated annealing of the 65 °K defects at 4.2 °K during excitation with less-than-band-gap filtered light and at 30 °K during excitation with monochromatic light of energy greater than the band gap. This model also predicts an interstitial migration energy of 0.005 eV as well as a temperature-dependent radiation-annealing rate in the 5-15 °K temperature range in good agreement with recent data obtained by Hyatt and Koehler.