Effects of electron irradiation on P-type germanium at liquid helium temperatures using AC hopping conductivity

P-type germanium single crystals (8 X 1014 Ga/cm3 and 6 X 1015 Ga/cm3) were irradiated with 1.1 MeV electrons at pUmped liquid helium temperatures and defect production and annealing studied using ac hopping conductivity. Production rates obtained from measurements at 1.5 K and 104 Hz were .6 cm- l for samples doped 6 X 10 15 Ga/cm 3 and .11 cm -1 for samples doped 8 X 10 14 Ga/cm3. Above 1014 e/cm2 fluence the production rates for the higher doped samples decreased to approxl. mately .06 cm -1 at 10 15 e/cm 2 fluence except for one sample which was anomalous. No such long irradiation of the low doped samples was made. The apparent inconsistency between these results and production rates of less than 3 X 10 -4 cm -1 observed by previous workers has been resolved by introducing a donor level for the defect produced by irradiation near the chemical acceptor level, so that the defect would be neutral at temperatures near 30 K and charged +1 at 1.5 K. Some surface effects were seen which did not affect production rate measurements at 1.5 K more than +10% but did influence annealing behavior at 100 K. The fact that the production rate observed increases with the impurity concentration leads one to propose that some defects must be mobile at the irradiation temperatures, which were usually 1.8 K. The fact that the production rate was 0.11 cm -1 +27% in the low doped p-type samples instead of 1.4 cm -1 or 0.95 + .05 cm- l as observed by other workers in n-type samples of similar dopant concent ration also supports this conclusion. This led to the suggestion that germanium and silicon are similar as far as lattice vacancy and interstitial behavior. The similarity of the migration energies of the doubly negative vacancy in silicon to the activation energy of 65 K stage in n-type germanium thus ihdicates that this stage could be due to vacancy migration. The migration energy of the neutral vacancy in silicon is similar to the activation energy of the 200 K stage in p-type germanium observed by other workers.U of I Onlydissertation/thesi