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