Electron Irradiation ofp-Type Germanium at 4.2°K

Abstract

Degenerate $p$-type germanium samples ($p_0\simeq {10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$) have been irradiated at 4.2°K with 4.5-MeV electrons from a microwave linear accelerator. Measurements of electrical conductivity and Hall effect have been made during the irradiation and later infrared illumination and heating. Small changes occur during the irradiation and may be described by a carrier removal rate of 0.4 ${\mathrm{cm}}^{-1\mathrm{}}$. Under the same conditions $n$-type Ge has a removal rate 25 times larger. This result is also in contrast to the case of 1.1-MeV electron irradiation of $p$-type Ge, where the changes are immeasurably small. Subsequent illumination-induced changes lower the conductivity and may be represented as the sum of two components, each exponential in the time of illumination. Two processes may also be observed during the heating. One, occurring between 30 and 90°K, restores the conductivity; another, between 70 and 110°K, has the reverse effect. Observation of both of the annealing processes is related to the duration of prior illumination. From this information relationships between the annealing processes and the stages of illumination-induced change are deduced. A crude analysis of the annealing is attempted and possibilities for the mechanisms are discussed.