Carrier-Concentration Dependence of Electron-Phonon Scattering in Te-Doped GaSb at Low Temperature

The thermal conductivity K between 5 and 100^∘{}K was measured on Te-doped samples with excess donor concentrations n ranging between {~}10¹⁷ and 2×{}10¹⁸ cm^-3. At temperatures below that of the peak, K was observed to decrease with increasing n, this behavior being associated to electron-phonon scattering. The dependence of K on n was investigated by calculating the additional thermal resistivity Wₑₚ=1/K-1K₀ at 6^∘{}K, where K and K₀ are, respectively, the experimental and theoretical values of the thermal conductivity. The theoretical conductivity was deduced from the Callaway model, using as parameters the Casimir-boundary mean free path, point-defect scattering calculated from the Klemens relation, and phonon-phonon scattering deduced empirically from the results at higher temperatures. Wₑₚ was found to vary approximately as n₃₀₀^∘K1.7 or n_~6^∘K2.2. The excess thermal resistivity is most likely due to scattering of phonons by an electron gas. On the basis of the Ziman model, it is suggested that the observed Wₑₚ(n) behavior may arise from a variation of the effective mass m* with n, due to the nonparabolic (000) band. Tentatively, an alternative argument is considered. The low-temperature thermal conductivity of undoped p-type samples with hole concentrations of about 1.5×{}10¹⁷ cm^-3 was found to be much lower than that of Te-doped samples with comparable electron concentrations. This indicates that the strength of hole-phonon scattering in undoped material is more pronounced than that of electron-phonon scattering in Te-doped material.