Optical Imaging of Light-Induced Thermopower in Semiconductors

The traditional measurement of the thermoelectric Seebeck coefficient gives a global value for a given material. This method requires heating and electrical contacts. Here, we report a local optical measurement of carrier populations which are not in thermal equilibrium with the lattice of the material. This contactless method enables access to the local gradients of the two fundamental thermodynamical properties, namely the temperature and the electrochemical potential. Therefore, we can determine the Seebeck coefficient related to the light-induced thermoelectric properties of the material. Moreover, we demonstrate the linear relationship between voltage and temperature gradients at a micrometer scale.