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

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^∘{}K. A linear increase in the additive thermal resistivity near 50^∘{}K is observed upon bombardment. The results yield 1/K-1K₀=(3.15±0.2)×10^-19 cm-deg/W per 2-MeV electron/cm². The experimental ratio of the point-defect thermal resistivity to the induced lattice strain at 50^∘{}K is (1/K-1K₀)(3ΔLL)=(1.0±0.2)×10⁴ 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 1/K-1K₀=(94±10)×10²C 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^∘{}K with all measurements made at 50^∘{}K demonstrate low-temperature annealing in GaAs. Annealing is observed to begin near 55^∘{}K and accelerate near 190^∘{}K. About 70% of the additive thermal resistivity stable at 50^∘{}K anneals below 325^∘{}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^∘{}K the defects anneal as point defects. For anneal temperatures between 325 and 575^∘{}K the point defects no longer remain isolated, and clustering or precipitation is suggested.