Effects of Electron Irradiation on the Thermal Conductivity ofn- andp-Type Germanium

The change in the low-temperature thermal conductivity $K$ of antimony-doped germanium was investigated in the $n$-to-$p$-type conversion region induced by 4-MeV electron irradiation (1.3×${10}^{17}$ to 1.6×${10}^{18}$ electrons/${\mathrm{cm}}^2$) performed at about 40°C. The thermal conductivity was found to decrease in the neighborhood of the peak and just below it, after the first electron dose (1.3×${10}^{17}$ electrons/${\mathrm{cm}}^2$). With higher electron fluxes, $K$ increased over the whole temperature range 5-80°K, reaching values higher than that of unirradiated germanium. The initial decrease of $K$ is at present not well understood, but is likely to be related to scattering of phonons by bombardment-introduced levels. The further increase of $K$ appears to be characteristic of the depletion of donor electrons by radiation-induced acceptor defects. This explanation is consistent with the Keyes model relative to scattering of phonons by occupied donors. No noticeable change in $K$ was obtained in $p$-type germanium for electron doses up to 1.7×${10}^{18}$ electrons/${\mathrm{cm}}^2$. This behavior indicates that either the radiation-induced levels involve no particular modification of the initial scattering mechanisms, or most likely the defect introduction rate is much lower than in $n$-type, the small amount of defects produced being of negligible effect on $K$.