Control of Thermoelectric Properties of ZnO using Electric Double Layer

TL;DR

This study demonstrates how an electric double layer transistor can effectively tune the thermoelectric properties of ZnO by controlling carrier concentration, inducing metallic behavior and optimizing the power factor.

Contribution

It introduces a method to modulate ZnO's thermoelectric properties using EDLT, providing a new approach for thermoelectric material optimization.

Findings

Resistivity and thermopower decrease with gate voltage above 2V.

Metallic behavior emerges with weak temperature dependence of resistivity.

Induced metallic layer estimated to be about 10nm thick.

Abstract

We have successfully controlled thermoelectric properties of ZnO by changing carrier concentration using an electric double layer transistor (EDLT) which is a feld effect transistor gated by electrolyte solution. The resistivity and the thermopower decreased abruptly by applying gate voltage larger than a threshold voltage ( 2V), indicating the increase of carrier concentration on the ZnO surface. The temperature dependence of resistivity became metallic, which is characterized by weak temperature dependence of the resistivity, when gate voltage exceeded 2V. Corresponding to the resistivity, the temperature dependence of thermopower changed remarkably. The thickness of the induced metallic layer was estimated to be about 10nm from the critical carrier concentration of metal-insulator transition, and the power factor was calculated to ~8*10-5Wm-1K2. Although the power factor is not as large as bulk ZnO ceramics of optimum doping condition, EDLT is considered to be a useful way to optimize thermoelectric properties by tuning carrier concentration.