Ultrahigh Detectivity Broad Spectrum UV Photodetector with Rapid Response Speed Based on p-β Ga 2 O 3 /n-GaN Heterojunction Fabricated by a Reversed Substitution Doping Method.

An excellent broad-spectrum (220-380 nm) UV photodetector, covering the UVA-UVC wavelength range, with an ultrahigh detectivity of ≈10 15  cm Hz 1/2 W -1 , is reported. It is based on a p-β Ga 2 O 3 /n-GaN heterojunction, in which p-β Ga 2 O 3 is synthesized by thermal oxidation of GaN and a heterostructure is constructed with the bottom n-GaN. XRD shows the oxide layer is (-201) preferred oriented β-phase Ga 2 O 3 films. SIMS and XPS indicate that the residual N atoms as dopants remain in β Ga 2 O 3 . XPS also demonstrates that the Fermi level is 0.2 eV lower than the central level of the band gap, indicating that the dominant carriers are holes and the β Ga 2 O 3 is p-type conductive. Under a bias of -5 V, the photoresponsivity is 56 and 22 A W -1 for 255 and 360 nm, respectively. Correspondingly, the detectivities reach an ultrahigh value of 2.7 × 10 15  cm Hz 1/2 W -1 (255 nm) and 1.1 × 10 15  cm Hz 1/2 W -1 (360 nm). The high performance of this UV photodetector is attributed mainly to the continuous conduction band of the p-β Ga 2 O 3 /n-GaN heterojunction without a potential energy barrier, which is more helpful for photogenerated electron transport from the space charge region to the n-type GaN layer.