β-Ga2O3 solar-blind deep-ultraviolet photodetector based on annealed sapphire substrate

A vacuum annealing was conducted on c-plane sapphire substrate in a plasma-assisted MBE system prior to the epitaxial growth of β-Ga2O3 film. Accordingly, both the crystal structures of epitaxial films and the device performance of fabricated metal-semiconductor-metal photodetectors were comparatively investigated based on the as-supplied and annealed sapphire substrates. The AFM result showed a large number of protrusions distributed uniformly on the surface of annealed sapphire substrate, proving an effective high-temperature reconstruction by such a pretreatment. Moreover, the β-Ga2O3 epitaxial film exhibited a significantly improved crystalline quality by adopting the annealed sapphire substrate as revealed by the XRD measurement. Accordingly, the carrier mobility could be improved due to the suppression of impurity scattering related to structural disorders, resulting in the observed significant increase of both dark and photo currents in photodetector. As a result, its DUV responsibility was improved from 44 A/W to 153 A/W. However, some degradations in photo-to-dark current ratio and response time appeared, which can be attributed to the reduction in the crystallographic defects impacting internal gain and carrier recombination, respectively. This work may pave an alternative way for the fabrication of high-performance β-Ga2O3 solar-blind DUV photodetector, especially for high responsibility.