Oxygen mediated optical and electrical property modification of RF sputtered Ga2O3 thin films for photodetector application

The deep UV photodetectors (DUV-PDs) are technologically important for diverse applications, ranging from environmental monitoring, space communication etc. Among all solar blind materials Ga₂O₃ thin film shows its strong contention owing to its intrinsic solar-blind nature. However, the PD’s efficiency can be significantly affected by the defects such as oxygen vacancies (VO). Both the deficiency and surplus of oxygen during Ga₂O₃ thin film deposition can result in the formation of carrier scattering centers, sub-bandgap absorption, and leakage channels. In this work, we have studied the impact of oxygen flow rate (OFR) on the optical and electrical properties of RF sputtered Ga₂O₃ thin film. The Ga₂O₃ thin films were deposited on p-Si at room temperature, where the Ar to O₂ ratio has been varied from 1:0, 1:1, to 1:2 to maintain the O₂ poor and O₂ rich condition. The XRD spectrum shows the presence of two peaks positioned at ~33.0° , and ~64.5° , which are further identified as β(-202), and β(-313), respectively for samples grown without oxygen. The top view FESEM images confirm the uniform film growth for both O₂ rich conditions while some isolated bubble-like and grain-like structures are witnessed in ratios 1:0, and 1:1, respectively. The change in optical bandgap for all the samples is determined using diffuse reflectance spectra which show the bandgap values lie in the range of 4.1 eV-4.2 eV. Furthermore, the deconvoluted photoluminescence spectra (in the range of λ=300-500 nm) show the change in different types of V_o defects originating due to OFR induced structural asymmetry in the Ga₂O₃ thin film. Finally, the change in dark current in Ga₂O₃/p-Si heterojunctions is estimated from current-voltage (I-V) characteristics to understand the effect of OFR on its electrical properties for future DUV detectors.