Thermal transport in molecular beam epitaxy grown Si1-xGex alloy films with a full spectrum of composition (x=0-1)

The thermal properties of Si1-xGex alloys are important for two major reasons: one is their applications in high-temperature thermoelectrics and the other is the increasing heat dissipation demand for high power density devices. However, the large lattice mismatch between silicon and germanium leads to tremendous difficulties to obtain high-quality Si1-xGex thin films, especially when x>0.5. In this study, we obtained a series of high crystalline quality Si1-xGex thin films with x covering all the way from 0 to 1 on Si substrates by molecular beam epitaxy. The out-of-plane thermal conductivities of these Si1-xGex films were measured by the time-domain thermoreflectance approach. Results show that while the thermal conductivity can vary significantly with composition, it only changes marginally in the temperature range of 100K-300K for a specific Ge content x. A theoretical analysis indicates that alloy and boundary scatterings are the dominant mechanisms for the thermal transport in these Si1-xGex (x=0-1) alloy films.