Thermal conductivities of quantum well structures

This work analyzes the size and the boundary effects of a gallium arsenide- (GaAs) based quantum well (QW) structure on the thermal conductivity of the well material. Calculations show that the order of phonon mean free path (MFP) is equal to or even longer than the typical dimension of the well (-200 A or less). Holland's model is applied to match the thermal conductivity data of bulk GaAs from 2 to above 600 K. The equation of phonon radiative transfer (EPRT) developed from the Boltzmann transport equation is then introduced for the heat transport in the QW structure. Boundary conditions are built from the diffuse phonon mismatch theory, and approximate solutions are obtained for the cases of heat flow perpendicular and parallel to the well. Results show that the thermal conductivity of the quantum well can be one order-of-magnitude lower than that of its corresponding bulk form at room temperature. The size and boundary effects also cause anisotropy of the thermal conductivity, even though the unit cell of GaAs is cubic.