Properties of Amorphous Transparent Conductive In-Ga-Zn Oxide Films Deposited on Fused Quartz by the PLD Method

Abstract

Transparent conductive oxide (TCO) films of In-Ga-Zn-O were deposited by sputtering, for applications involving shorter wavelengths than visible light wavelengths. The films were deposited on fused quartz at a substrate temperature of 250° by pulsed laser deposition (PLD) using a pulsed KrF excimer laser (λ=248 nm). The targets were synthesized by mixing In2O3-Ga2O3-6ZnO powders and Ga2O3+3ZnO powders. Weight % of the mixed Ga2O3+3ZnO powders was estimated by x, where x was changed from 0 to 0.2 in order to increase the fraction of Ga atoms in the film. Near the stoichiometric composition of In, Ga and Zn, we obtained low resistivity films and high carrier mobility. All the films deposited were amorphous. The optical bandgap energy was increased with increasing Ga content. With appropriate incorporation of extra Ga in the target, we could deposit stoichiometric In-Ga-Zn-O amorphous films. We obtained the lowest resistivity of 3 × 10-3 Ωcm and a high Hall mobility of 20-25 cm2/Vs. The carrier concentration was 1 × 1020 cm-3. The optical band gap energy was changed from 3.91 to 4.06 eV with increasing x value from 0 to 20 wt%. It was confirmed that the slight deviation from the stoichiometric composition did not influence the electrical properties. Even for a thickness of 50-80 nm, the film properties were the same as those of much thicker films. The present films are very homogeneous and the surface is very flat, due to the fact that the films are amorphous. [DOI: 10.1380/ejssnt.2009.273]