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.