Si content variation and influence of deposition atmosphere in homoepitaxial Si-doped β-Ga2O3 films by pulsed laser deposition

Abstract

Carrier concentration control by impurity dopants in epitaxial Ga2O3 thin films is progressing to deliver high mobility films for device structures. Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on (010) β-Ga2O3 substrates from Ga2O3 targets with 0.01–1 wt. % SiO2 yielding films with an electron mobility range consistent with other vapor growth techniques. Single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction was observed, with a high Si dopant level causing film tensile strain as indicated by both techniques. The influence of oxygen on conductivity using different O2 pressures during deposition and O2/Ar mixtures with a fixed working pressure of 1.33 Pa was determined. With this optimized deposition pressure and atmosphere condition, a carrier concentration and mobility range of 3.25 × 1019 cm−3–1.75 × 1020 cm−3 and 20 cm2/V s–27 cm2/V s was achieved in films from Ga2O3-0.025 wt. % SiO2 and Ga2O3-1 wt. % SiO2 targets, respectively. A highest conductivity of 798 S cm−1 was achieved in films deposited at 550 °C–590 °C with targets of 0.05–1 wt. % SiO2. The electrically active and chemical Si content in films deposited at 550 °C was found to exceed the expected Si ablation target composition in all cases except the highest 1 wt. % SiO2 target attributed to imprecise target manufacturer compositional control at low SiO2 doping levels. Diminished electrical and structural quality films resulted from all targets at a 450 °C deposition temperature.