Enhanced thermoelectric figure-of-merit in boron-doped SiGe thin films by nanograin boundaries

TL;DR

This study demonstrates that boron-doped SiGe thin films with nanograin boundaries exhibit significantly improved thermoelectric performance, achieving a record ZT of 0.2 at room temperature due to reduced in-plane thermal conductivity.

Contribution

The paper reports the first high ZT in boron-doped SiGe thin films with nanograin boundaries, enhancing thermoelectric efficiency through grain boundary engineering.

Findings

Achieved ZT of 0.2 at 300 K, doubling previous records.

Observed 50% lower in-plane thermal conductivity due to nanograin boundaries.

Demonstrated scalable LPCVD process for high-performance thermoelectric films.

Abstract

Boron-doped polycrystalline silicon-germanium (SiGe) thin films are grown by low-pressure chemical vapor deposition (LPCVD) and their thermoelectric properties are characterized from 120 K to 300 K for the potential applications in integrated microscale cooling. The naturally formed grain boundaries are found to play a crucial role in determining both the charge and thermal transport properties of the films. Particularly, the unique columnar grain structures result in remarkable thermal conductivity anisotropy with the in-plane thermal conductivities of SiGe films about 50% lower than the cross-plane values. By optimizing the growth conditions and doping level, a high figure of merit (ZT) of 0.2 for SiGe films is achieved at 300 K, which is about 100% higher than the previous record for p-type SiGe alloys, mainly due to the significant reduction in the in-plane thermal conductivity caused by nanograin boundaries. The low cost and excellent scalability of LPCVD render these high-performance SiGe films ideal candidates for thin-film thermoelectric applications.