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.
Highlights
Si content variation and influence of deposition atmosphere in homoepitaxial Si-doped -Ga2O3 films by pulsed laser deposition
The emerging field of β-Ga2O3 devices addressing future power switching applications is expanding to a large extent as a result of recent materials improvements including high quality native substrates and the ability to shallow dope epitaxial β-Ga2O3. β-Ga2O3 substrates have been fabricated by the Czochralski,[1,2,3,4] floating-zone,[5,6] and edge-defined film fed (EFG)[7,8] growth methods only EFG is currently commercially available
Initial field effect transistors (FETs) have been shown with channel layers of Sn-doped Ga2O3 by molecular beam epitaxy (MBE),[9,10,11] Si ion implanted Ga2O3 by MBE,[12,13] Sn-doped Ga2O3 by metal organic vapor phase epitaxy (MOVPE),[14,15] and Sidoped Ga2O3 by hydride vapor phase epitaxy (HVPE).[16]
Summary
Si content variation and influence of deposition atmosphere in homoepitaxial Si-doped -Ga2O3 films by pulsed laser deposition. (Received 5 July 2018; accepted 11 September 2018; published online 1 October 2018)
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