Alpha-Particle Irradiation of Ge at 4.2°K

Degenerate $n$- and $p$-type germanium samples were irradiated at 4.2°K with polonium alpha-particles. The irradiation removed carriers at a rate of $2.84\times {10}^4 \mathrm{electrons}/\alpha$-cm in $n$-type samples and $1.32\times {10}^4 \mathrm{holes}/\alpha$-cm in $p$-type samples. Thermal recovery was studied up to 78°K. No measurable recovery was observed below 22°K. Upon warming to 78°K the irradiation-induced changes of Hall coefficient decreased by about the same fraction, 25% and 22%, respectively, in $n$-type and $p$-type samples, showing that the same fractions of donor and acceptor defects were annealed out. Experiments made with various annealing procedures, using electrical resistivity as a measure, indicated that there were two distinct regions of thermal recovery, with maximum rates of change occurring near 33°K and 67°K. The low-temperature process appears to follow a first-order reaction with a unique activation energy of about 0.02 ev. It may be due to the recombination of interstitials with nearby vacancies. The higher temperature process does not yield to simple analysis.