Intrinsic Modulation Doping Enhances the Thermoelectric Performance of Monolayer GaGeTe

Modulation doping is a well-known approach for improving the efficiency of bulk thermoelectrics, yet its application to 2D materials has remained elusive. Our thorough first-principles calculations reveal a unique intrinsic modulation doping in monolayer GaGeTe that synergistically raises its electrical transport coefficients while dwarfing its lattice heat transport, resulting in a high thermoelectric figure of merit, zT. Herein, we envision 2D GaGeTe as a chair-like germanene monolayer shrouded by two GaTe layers. The germanene layer donates electrons to the outer GaTe, creating a spatial separation between the electron-donation center and charge transport channels, a feature that suppresses free carrier scattering. Our accurate electron–phonon calculations explain that electrical transport in GaGeTe results from the metallic nature of germanene combined with the Mexican-hat shape of the GaTe valence band. The superior electrical and poor heat transport coefficients turn GaGeTe into a promising p-type thermoelectric monolayer working at moderate carrier concentrations of ≈1013 cm–2. The presented results put forward a distinct design approach for identifying competent thermoelectrics among 2D materials whose frail structures cannot tolerate heavy doping.