Change in Thermal Conductivity upon Low-Temperature Electron Irradiation: GaAs

Abstract

Measurements of the change in thermal conductivity of high-purity single-crystal GaAs were made upon 2-MeV electron irradiation and annealing. Two GaAs samples were irradiated at maximum temperatures of 100 and 80\ifmmode^\circ\else\textdegree\fi{}K. A linear increase in the additive thermal resistivity near 50\ifmmode^\circ\else\textdegree\fi{}K is observed upon bombardment. The results yield $\frac{1}{K}\ensuremath{-}\frac{1}{{K}_{0}}=(3.15\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}$ cm-deg/W per 2-MeV electron/${\mathrm{cm}}^{2}$. The experimental ratio of the point-defect thermal resistivity to the induced lattice strain at 50\ifmmode^\circ\else\textdegree\fi{}K is $\frac{(\frac{1}{K}\ensuremath{-}\frac{1}{{K}_{0}})}{(\frac{3\ensuremath{\Delta}L}{L})}=(1.0\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{4}$ cm-deg/W. Using estimates for the introduced defect concentration (based upon the change in strain rate as a function of electron energy) together with the observed increase in thermal resistivity, one obtains $\frac{1}{K}\ensuremath{-}\frac{1}{{K}_{0}}=(94\ifmmode\pm\else\textpm\fi{}10)\ifmmode\times\else\texttimes\fi{}{10}^{2}C$ cm-deg/W, where $C$ is the fractional point-defect concentration. This value is intermediate between those predicted by the point-defect scattering theories of Klemens and Ziman. Isochronal anneals carried out above 50\ifmmode^\circ\else\textdegree\fi{}K with all measurements made at 50\ifmmode^\circ\else\textdegree\fi{}K demonstrate low-temperature annealing in GaAs. Annealing is observed to begin near 55\ifmmode^\circ\else\textdegree\fi{}K and accelerate near 190\ifmmode^\circ\else\textdegree\fi{}K. About 70% of the additive thermal resistivity stable at 50\ifmmode^\circ\else\textdegree\fi{}K anneals below 325\ifmmode^\circ\else\textdegree\fi{}K. Definite minima are observed in the temperature dependence of the thermal conductivity, suggesting localized-impurity-mode scattering. The annealing, however, takes place over too large a temperature range to be due to a single thermally activated process. The change in shape of the temperature dependence of the thermal conductivity upon annealing indicates that below 325\ifmmode^\circ\else\textdegree\fi{}K the defects anneal as point defects. For anneal temperatures between 325 and 575\ifmmode^\circ\else\textdegree\fi{}K the point defects no longer remain isolated, and clustering or precipitation is suggested.