High Power Factor in Polycrystalline InGaSb Thin Films via Nanoscale Compositional Fluctuations

III-V compound semiconductors are promising candidates for thin-film thermoelectric materials because their narrow-bandgap alloys can exhibit a thermoelectric response near room temperature. In this study, we systematically investigated polycrystalline InGaSb thin films deposited on glass substrates and identified the deposition temperature and In flux as key parameters governing phase competition and nanoscale compositional fluctuations. By modulating the In supply, discontinuous In-rich precipitates were formed while the matrix composition was systematically tuned. Variation of the deposition temperature further enabled control of structural disorder and nanoscale features, as evaluated by Raman analyses. At the highest deposition temperature (560 °C) that maintained continuous films, increased disorder correlated with an enhanced Seebeck coefficient without a significant reduction in electrical conductivity. As a result, a high power factor of 1200 µW m-1 K-2 was achieved near room temperature. These findings demonstrate that growth-parameter-driven microstructure and phase control provide an effective strategy for enhancing thermoelectric performance in multicomponent polycrystalline III-V thin films.