Growth and characterization of F-doped α-Ga2O3 thin films with low electrical resistivity

Abstract

F-doped α-Ga2O3 thin films with low electrical resistivity were epitaxially grown on c-plane α-Al2O3 substrates by means of mist chemical vapor deposition. The resistivity of the α-Ga2O3 thin films was decreased dramatically by incorporating F into α-Ga2O3, achieving a minimum resistivity of 6.2 × 10−2 Ω·cm in a 1050 nm thick film grown from a precursor solution with a [F]/[Ga] ratio of 20%. Further, the carrier concentration was 1.3 × 1019 cm−3, and the Hall mobility was 4.6 cm2/Vs with the [F]/[Ga] ratio of 20% and a film thickness of 1560 nm. Secondary ion mass spectrometry revealed that the F concentration incorporated into the α-Ga2O3 thin film was approximately 1 × 1020 cm−3, and the activation ratio was approximately 10%. The higher [F]/[Ga] ratio in the precursor solution caused lower crystallinity, as demonstrated by X-ray diffraction rocking curves. For all [F]/[Ga] ratios, as the film thickness increased to approximately 1000 nm, the electrical resistivity of the thin films drastically decreased. In the thinner films, the dislocations at the interface between the α-Ga2O3 thin films and the α-Al2O3 substrates are thought to trap electrons and compensate the free carriers or deteriorate the mobility.