Free-carrier localization and electron–phonon interaction in transparent conductive oxide films

Abstract

We present the size effects on the electrical and optical properties of high Hall mobility transparent conductive oxide (TCO) films, where the size effects were characterized by the disorder parameter. First, we deposited amorphous W-doped In₂O₃ (IWO) films with thicknesses ranging from 5 to 10 nm on glass substrates using reactive plasma deposition with dc-arc discharge. Then, we obtained polycrystalline IWO films by solid-phase crystallization, and elucidated the dominant factors determining the states of the carrier electrons and their carrier transport of the films. Decreasing the thickness from 10 to 5 nm, while retaining the carrier concentration, leading to a 2D-like films with induced a lattice disorder, resulting in reduced Hall mobility. A theoretically obtained electron–phonon coupling factor, which is found to be governed by the Debye temperature, carrier concentration, and disorder parameter, provided the cause of the above carrier transport behavior. In addition, based on the above electron–phonon coupling factor, we propose theoretical predictions of materials design to achieve high carrier transport ultra-thin TCO films.