Length and Resistivity Changes in Germanium upon Low-Temperature Deuteron Irradiation and Annealing

Simultaneous measurements of the length change and resistivity of high-purity germanium single crystals were made upon irradiation and annealing. The specimens were initially irradiated at 25°K with deuterons of average energy 10.2 Mev to an integrated flux of 6.2×${10}^{16}$ deuterons/${\mathrm{cm}}^2$ and annealed to room temperature. The specimens were then irradiated at 85°K to an additional flux of 9.2×${10}^{16}$ deuterons/${\mathrm{cm}}^2$ and annealed to 364°K. The specific length expansion for both bombardments was $\frac{\Delta L}{L}=(1.5\mathrm{}\pm 0.3)\times {10}^{-21\mathrm{}}/(\mathrm{deuteron}/{\mathrm{cm}}^2)$. The annealing after both irradiations showed a gradual recovery of the expansion which was observable only after warming to above 200°K. The precise determination of the onset of annealing was limited by the accuracy of the expansion measurements (∼20%). Recovery was ∼50% complete by 300°K and ∼85% complete by 360°K. The resistivity measurements agreed generally with previous results. A large increase in resistivity occurred during the low-temperature bombardments. The specimens became $p$-type after bombardment and annealing. On the first warmup after the bombardment at 25°K the resistivity decreased irreversibly by a factor of ${10}^6$ between 65°K and 300°K with a large part of the decrease coming apparently between 150°K and 225°K. On the warmup from the second bombardment at 85°K an irreversible resistivity increase occurred on warming to 140°K. The resistivity then decreased irreversibly by a factor of ${10}^3$ between 150°K and 200°K. Extensive resistivity annealing, therefore, occurred in an earlier stage of the recovery process than did the experimentally observable length change annealing.