Thermal conductivity of Si/Ge superlattices: A realistic model with a diatomic unit cell

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Abstract
This paper considers the effects of a realistic description of phonons in diamondlike semiconductors and their conversion on the abrupt heterointerfaces on the thermal conductivity of the superlattice (SL). Due to the much larger mass of Ge atoms in comparison to Si, the most probable acoustic phonons in Si layers at room temperature have no counterpart in Ge. In simplified models where Si and Ge are simulated by monatomic crystals with fitted parameters, this leads to the highly efficient trapping of high-energy acoustic phonons in Si layers and drastic reduction of the SL thermal conductivity. The proposed approach incorporates the optical branches and the effective conversion of the phonons at interfaces extends the temperature range for which the model is valid and thereby leads to corrections to predicted thermal conductivity.