We present a detailed study of the charge transport, infrared optical reflectivity, and thermal transport properties of $n$-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustic phonon scattering alone. We applied the first-order nonparabolicity approximation to extract the density-of-states effective mass as a function of doping both at room temperature and at 700 K. The results are compared to those of a parabolic band model and in light of doping-dependent studies of the infrared optical reflectivity. The thermal conductivity behavior as a function of temperature shows a strong deviation from the expected Debye-Peierls high-temperature behavior (umklapp dominated) indicating an additional heat-carrying channel, which we associate with optical phonon excitations. The correlation of the thermal conductivity observations to the high-temperature carrier mobility behavior is discussed. The thermoelectric figure of merit exhibits a promising value of $\sim$ 0.8 at 700 K at $\sim 1.5\times {10}^{19}$ cm${}^{-3}$.

• Received 10 August 2011

DOI:https://doi.org/10.1103/PhysRevB.84.155207