Semiconductor-based thermal wave crystals

One-dimensional phononic crystals made of silicon (Si) and germanium (Ge), both of which are materials commonly used in semiconductor devices, are shown to be effective in inducing bandgaps in the dispersion of heat flow at the nanoscale. Numerical approaches are used to understand the dispersion and propagation of thermal waves in Si–Ge phononic crystals. The results show for the first time how nanostructuring could yield band gaps in the dispersion of thermal phonons in the GHz range. We arrive at conditions that can yield bandgaps as high as 40 GHz; this is a bandgap that exceeds the value reported thus far. Variations in the unit cell dimensions are studied to understand the corresponding evolution in the bandgap frequencies. The control of heat using such proposed media holds promise for better heat management solutions for modern electronic devices, nanoscale sensing as well as for novel applications including the development of thermal diodes and thermal cloaks.