Factors limiting carrier transport of ultrathin W-doped In2O3 films

Abstract

Polycrystalline ultrathin 5 nm-thick n-type W-doped In2O3 (p-IWO) films with a significantly high Hall mobility (μH) of 57.7 cm2 (Vs)−1 were successfully fabricated by the under-vacuum solid-state crystallization of amorphous IWO (a-IWO) films. a-IWO films with thicknesses (t) ranging from 5 to 50 nm were deposited on glass substrates without intentionally heating the substrates by reactive plasma deposition with direct current arc discharge. The source used for the film growth was a sintered In2O3 pellet with a WO3 content of 1.0 wt.% (corresponding to 0.6 at.%). We investigated the t dependence of the carrier transport mechanism of IWO films having the mean free paths of carrier electrons similar to t based on an empirical model with combined surface and interface scattering. The qualitative analysis of the relationship between μH and the ratio of the mean free path of carriers in the bulk material of n-type to t proved that the contribution of the combined scattering to μH is significantly dominant for p-IWO films at t of less than 10 nm. In such films that have very smooth surface with roughness of less than 0.78 nm and interface with roughness of less than 1 nm, the combined specularity parameter (≤ 2) is found to be 1.6 to 1.7, resulting in a high μH.