Abstract
Thermal conductivity of bulk Si0.5 Ge0.5 at room temperature has been calculated using density functional perturbation theory and the phonon Boltzmann transport equation. Within the virtual crystal approximation, second- and third-order interatomic force constants have been calculated to obtain anharmonic phonon scattering terms. An additional scattering term is introduced to account for mass disorder in the alloy. In the same way, mass disorder resulting from n- and p-type dopants with different concentrations has been included, considering doping with III-group elements (p-type) such as B, Al, and Ga, and with V-group elements (n-type) such as N, P, and As. Little effect on the thermal conductivity is observed for all dopants with a concentration below 1021 cm−3. At higher concentration, reduction by up to 50% is instead observed with B-doping in agreement with the highest mass variance. Interestingly, the thermal conductivity even increases with respect to the pristine value for dopants Ga and As. This results from a decrease in the mass variance in the doped alloy, which can be considered a ternary system. Results are compared to the analogous effect on the thermal conductivity in doped Si.
Highlights
A detailed understanding of the mechanisms ruling over thermal transport is of great importance for many technological applications
Here, we focus on scattering events resulting from different mass variances and their effect on the lattice thermal conductivity in the Si0.5Ge0.5 alloy, which is of technological interest for thermoelectric applications
Since we focus on the influence of mass disorder without considering phonon–carrier interactions or effects from changes in chemical bonds, no further distinction is made between n- and p-type materials
Summary
A detailed understanding of the mechanisms ruling over thermal transport is of great importance for many technological applications. A promising approach in this respect is nanostructuration (Minnich et al, 2009; He, Donadio, and Galli, 2011; Ferre Llin et al, 2013; Savic et al, 2013). Another efficient way to reduce the thermal conductivity is through introduction of mass disorder, which can be achieved by alloying as successfully shown, for example, in SiGe materials (Steele and Rosi, 1958; Abeles, 1963; Garg et al, 2011; Melis and Colombo, 2014). Already at a Ge content as low as 3%, the thermal conductivity is reduced by a remarkable 84% with respect to pure Si (Garg et al, 2011)
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