Studies of Radiation Damage in Degenerate Silicon Irradiated at Low Temperatures

Abstract

Pulled (Czochralski) and float-zone $n$-type (NC,NF) and $p$-type (PC,PF) degenerate Si samples were irradiated in the 10-140°K temperature range, using 1-MeV electrons, and were studied by observing changes which occur in the dc conductivity $\sigma$ and Hall coefficient $R_H$ as a result of bombardment and various thermal treatments. For PC and PF, carrier removal rates remained practically constant at 0.7 and 1.1 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively, for irradiation temperatures between 7 and 90°K. In contrast, NC and NF removal rates increased nearly exponentially with irradiation temperature above approximately 60°K, while below ≅60°K they were exceedingly small (${\mathrm{cm}}^{-1\mathrm{}}$). Radiation-induced recovery due to 350-keV electrons was observed in $n$-type Si. This effect exhibits a strange temperature dependence, being quite efficient below a characteristic temperature and very inefficient above that temperature. The kinetics of radiation annealing at a given temperature is a superposition of two first-order processes. The metastable-pair model is compared with one based on a mobile interstitial. Defects introduced into degenerate Si at low temperatures show high resistance to thermal annealing, in contrast to the behavior of nondegenerate material. Isochronal annealing runs indicate that complete recovery occurs only around 1000°K. Some of the recovery stages are tentatively identified with specific defect structures previously reported in the literature. Detailed results of isothermal annealing experiments in the first recovery stage of $p$-type Si (295-265°K) are given.