Thermovoltaic Effect, a Novel Phenomenon on Nonpolar ZnO (1010) Surfaces

The discovery of a novel physical phenomenon will open up a new field of study. Here, we demonstrate a novel phenomenon, the thermovoltaic effect observed on a nonpolar ZnO (101̅0) surface, which is completely different from the pyroelectric and thermoelectric effects. Temperature variation and the temperature gradient are not needed in this thermovoltaic effect. The short-circuit current and open-circuit voltage of the ZnO thermovoltaic device are 0.64 μA and 0.88 mV, respectively, under the thermal radiation of a rod-shaped heater (9.0 W). The thermovoltaic effect arises from the spontaneous electric field (Es) in the polar [0001] direction on the ZnO (101̅0) surface. The Es drives the directional movement of thermally created electrons along the [0001] direction, and the thermovoltaic effect is thus observed. This thermovoltaic effect opens the door to the study of thermovoltaic cells and provides direct evidence for the general polar structure theory.