Non-destructive tuning of thermoelectric power factor of ZnO by surface-confined optical gating

We have studied the complex relationship between the thermoelectric properties of Zinc Oxide (ZnO) thin films and their interaction with various atmospheric conditions and ultraviolet (UV) illumination. We focused on the dynamic changes in the Seebeck coefficient (SC) and conductivity of ZnO under varied environments, which are crucial for tuning the thermoelectric power factor (PF). ZnO films showed pronounced variations in their carrier concentration and mobility when exposed to UV light in air and argon atmospheres, which can be attributed to the interplay of oxygen adsorption and desorption on the ZnO surface. The profound effect of the oxygen interaction, evidenced in a depletion layer wider than the ZnO film itself, significantly changed the electron concentration, and affected the surface conductivity and thus, the thermoelectric PF of ZnO. The experiments revealed that the SC decreased with increasing carrier concentration and mobility under UV illumination, while the thermoelectric PF increased in both atmospheres, providing pivotal insights into the nondestructive optimization of the thermoelectric properties of ZnO through controlled surface-sensitive reactions and optical gating.