Deposition of Ga2O3 thin films by liquid metal target sputtering

TL;DR

This study demonstrates a high-rate, reactive pulsed DC magnetron sputtering method using a liquid gallium target to deposit amorphous and crystalline Ga2O3 thin films with controlled microstructure and optical properties.

Contribution

It introduces a novel sputtering approach with higher deposition rates from a liquid gallium target, achieving epitaxial growth and detailed microstructural characterization.

Findings

Deposition rate up to 37 nm/min at room temperature

Crystalline ta-Ga2O3 appears at 500C

Epitaxial films formed on c-sapphire above 600C

Abstract

This paper reports on the deposition of amorphous and crystalline thin films of Ga2O3 by reactive pulsed direct current magnetron sputtering from a liquid gallium target onto fused (f-) quartz and c plane (c-) sapphire substrates, where the temperature of the substrate is varied from room temperature (RT) to 800{\deg}C. The deposition rate (up to 37 nm/min at RT on f-quartz and 5 nm/min at 800{\deg}C on c-sapphire) is two to five times higher than the data given in the literature for radio frequency sputtering. Deposited onto unheated substrates, the films are X-ray amorphous. Well-defined X-ray diffraction peaks of \b{eta}-Ga2O3 start to appear at a substrate temperature of 500{\deg}C. Films grown on c-sapphire at temperatures above 600{\deg}C are epitaxial. However, the high rocking curve full width at half maximum values of {\approx} 2.4-2.5{\deg} are indicative of the presence of defects. A dense and void-free microstructure is observed in electron microscopy images. Composition analysis show stoichiometry close to Ga2O3 and no traces of impurities. The optical properties of low absorptance (<1%) in the visible range and an optical band gap of approximately 5 eV are consistent with the data in the literature for Ga2O3 films produced by other deposition methods.