ABSTRACT
We explain the significant reduction in the in-plane thermal conductivity of GaAs/AlAs superlattices as observed by T. Yao, Appl. Phys. Lett. 51, 1798 (1987.) We estimate that the average bulk-phonon mean free path l mfp = 115 nm is significantly longer than the superlattice layer thickness d = 5–50 nm. The GaAs/AlAs interfaces are generally smooth but does contain a finite density of both microroughness and monolayer island defects which cause an enhanced elastic and anharmonic phonon scattering. We treat this interface scattering as diffusive, i.e., providing a complete phonon thermalization. The resulting phonon Knudsen flow within the individual superlattice layers can account for the observed reduction of the in-plane superlattice thermal conductivity. We also consider the effects of a finite probability for reflection at the interfaces.
