Thermal conductivity of electron-irradiated CdS

Measurements were made of the change in low-temperature thermal conductivity of high-resistivity sulfur-compensated single-crystal CdS upon electron irradiation and annealing. Samples oriented parallel and perpendicular to the hexagonal c axis of CdS were irradiated with 2-MeV electrons below 25°K to fluences Φ totaling 7.8 × 10¹⁷ electrons/cm². The increase in the additive thermal resistivity at 11 °K on irradiation was found to be independent of the orientation of the sample, and $\frac{1}{K}-\frac{1}{K_0}=\left(5.5\times {10}^{-10}\right){\Phi }^{0.5}$ cm deg/W. Isochronal annealing measurements show almost complete annealing out of the additive thermal resistivity below room temperature, and recovery begins as low as 35 °K. There are three major annealing stages centered near 45, 75, and 225 °K. Annealing above 60 °K produces an anisotropic thermal conductivity for subsequent measurements below 20 °K. The anisotropic additive thermal resistivity is much greater if the temperature gradient is perpendicular to the c axis than if it is parallel. The anisotropic phonon scattering is attributed to the formation and temperature-dependent orientation of anisotropic defects. It is concluded that the defect orientation parallel to the c axis has the lowest energy, and measurements of the temperature dependence of the thermal conductivity parallel and perpendicular to the c axis give the equilibrium energy difference for reorientation to be ≈1.5×10⁻³ eV.