LONGITUDINAL PHONONS AND HIGH-TEMPERATURE HEAT-CONDUCTION IN GERMANIUM

Using the relaxation time approach, we present a new analysis of phonon conductivity which shows that at high temperature (T > theta(D), the Debye temperature), the longitudinal phonons are the dominant heat carriers in germanium. The present result, which is a consequence of the effect of phonon dispersion on the Callaway integral for lattice thermal conductivity, is contrary to the general belief that transverse phonons carry heat at T > theta(D). A qualitative justification has also been given for the three-phonon scattering parameters obtained.