  We present a detailed study of the charge transport, 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 acoustical phonon scattering alone. We
applied the first order non-parabolicity 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
the light of doping dependent studies of the infrared optical reflectivity. The
thermal conductivity behavior as a function of temperature shows 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 ~0.8 at 700K
at 1.5 x 10^{19}$ cm^-3.
