Thermal atomic layer deposition of Ga2O3 films using trimethylgallium and H2O

Abstract

The Atomic Layer Deposition (ALD) technique is regarded as an effective method for fabricating high-quality Ga2O3 thin films. Trimethyl gallium (TMG), with its high vapor pressure at room temperature (227 Torr), is widely utilized as a gallium precursor in this technique. For oxygen precursors, common choices include O3 and O2 plasma. However, the impact of H2O as an oxygen precursor on Ga2O3 thin films during Thermal Atomic Layer Deposition (TALD) remains insufficiently explored. This study investigates the temperature window and growth characteristics of Ga2O3 thin films, deposited using TMG and H2O as precursors, on sapphire substrates within the temperature range of 250–500 °C. At 250 °C, deposited Ga2O3 films exhibit an amorphous structure, whereas within the 300–500 °C substrate temperature range, they transition to the α-phase. The half-peak width (FWHM) narrows as the temperature increases, with characteristic peaks of the (0006) facets shifting to higher angles at 500 °C. STEM analysis reveals complete coherence between α-Ga2O3 films and the sapphire substrate, indicating a pseudo-crystalline structure formation. The growth rate of the films at 450 °C is 0.083 Å/cycle. Ga2O3 films prepared with H2O as the oxygen precursor exhibit Ga-rich properties, with (Ga + Al)/O atomic ratios between 0.88 and 0.91 across the 250–500 °C temperature range. The films’ roughness (Ra) ranges from 0.453 to 0.646 nm. Island-like particles form on the film surface within the 400–500 °C range, smoothing out as the temperature rises. The film’s band gap peaks at 5.50 eV at 450 °C. The reaction of TMG with H2O on sapphire substrates yields Ga2O3 films and CH4 by-products, akin to the trimethylaluminum process.