Quantifying thermal transport in amorphous silicon using mean free path spectroscopy

The wide application of amorphous materials in solar cells, memristors, and optical sensors has stimulated interest in understanding heat conduction in amorphous systems owing to their thermal management issues. Thermal transport in amorphous materials fundamentally differs from their crystalline counterparts due to the lack of long-range order. Despite great progress in understanding the thermal transport in crystalline materials over the past few decades from both first-principles computations and thermal transport characterizations, details of heat conduction in amorphous systems remain largely unknown. Here, we quantify different types of heat carriers in amorphous silicon using mean free path spectroscopy, with characteristic sizes down to 50 nm. We show that despite its disordered nature, more than half of thermal conductivity is contributed by propagating vibrational waves, which have mean free paths mostly above 100 nm. This provides direct evidence supporting the diversity of heat carriers in amorphous systems; some modes transport heat as propagating waves, while others do not. Our results suggest mean free path spectroscopy is a versatile tool for understanding thermal transport in disordered systems.