High thermoelectric performance of high‐mobility Ga‐doped ZnO films via homogenous interface design

Abstract

AbstractGa‐doped ZnO (GZO) thin films grown on sapphire substrates have been widely investigated as a promising transparent thermoelectric (TE) material. However, due to the large lattice mismatch and thermal expansion between the sapphire substrate and GZO film, strain‐induced lattice distortion impedes the transport of electrons, leading to low carrier mobility. In this study, ZnO homo‐buffer layers with different thicknesses were inserted between sapphire substrates and GZO films, and their effect on the TE properties was investigated. A thin ZnO interlayer (10 nm) effectively reduced the lattice mismatch of the GZO film and improved the carrier mobility, which contributed to the large enhancement in the electrical conductivity. Simultaneously, energy filtering occurred at the interface between GZO and ZnO, resulting in a relatively high density of states (DOS) effective mass and maintaining a high Seebeck coefficient compared to that of the unbuffered GZO films. Consequently, the GZO film with a 10 nm thick ZnO buffer layer possessed a high power factor value of 449 μW m−1 K−2 at 623 K. This study provides a facile and effective method for optimizing the TE performance of oxide thin films by synergistically improving their carrier mobility and enhancing their effective mass.