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The influence of oxygen partial pressure and annealing on the properties of thin films of β-Ga2O3 grown by pulsed laser deposition were studied. The Ga2O3 samples were deposited at a substrate temperature of 250 °C at an oxygen pressure of 0–50 mTorr and then annealed at a temperature of 600 °C. We observed the crystallinity of Ga2O3 enhanced with annealing and with increasing oxygen pressure. The full width at half maximum of annealed β -Ga2O3 ( 4 ¯ 01 ) peaks decreased, corresponding to the grain size increasing from 6.76 nm to 11.25 nm. The conductivity of the obtained, as-grown Ga2O3 films increased with oxygen pressure from 2.1 to 7.9 mScm−1. As a result, the conductance and the energy band gap of β-Ga2O3 without annealing were controlled by the oxygen partial pressure. This was attributed to the oxygen vacancies, based on the composition ratio between O and Ga ions. These results clearly showed that the energy band gap and conductance of β-Ga2O3 thin films could be controlled in such a way that could be utilized for high-performance photo-electronic devices.

We studied Si-doped Ga2O3 photodetectors with a metal-semiconductor-metal structure that were fabricated using pulsed laser deposition and a post-annealing process under an oxygen atmosphere in a temperature range from 500 °C to 800 °C. After post-annealing, the Si-doped Ga2O3 photodetectors with 500 °C was showed the highest photoresponsivity (0.34 A/W) and external quantum efficiency (166.23%), while the device with 800 °C was exhibited the fastest switching speeds (0.88 s/0.18 s) for the on/off switching. These results are due to changes in the defect densities from the chemical bond formation between Si and O atoms. Our results show that post thermal annealing of Si-doped β-Ga2O3 layers can modify the photodetector performance depending on applications for high photoresponsivity or fast response time.