Heavily doped, highly compensated epitaxial ScN thin films exceed Boltzmann thermopower limits

The Seebeck effect converts a temperature gradient into an electric voltage. However, conventional transport theories constrain this thermopower to a few millivolts per Kelvin in crystalline materials. We present experimental evidence of a Seebeck coefficient exceeding -124 millivolts per Kelvin near room temperature in heavily doped, highly compensated (HDHC) epitaxial scandium nitride (ScN) thin films. Random distribution of charged dopants in HDHC ScN are known to generate potential fluctuations that distort the electronic bands and give rise to percolative transport, and our results further reveal a power-law scaling between thermopower and electrical conductivity. In ultrathin films, the Rytova-Keldysh modifications of the Coulomb potential further amplify the potential fluctuations and enhance the Seebeck response. Our findings reveal a solid-state analog of electrolyte-like thermopower in a crystalline semiconductor.