Enhanced self-driven ultraviolet photodetection performance of high-k Ta2O5/GaN heterostructure

Abstract

Recently, high-k dielectric oxide-based MIS type ultraviolet (UV) photodetectors (PDs) have engrossed the researchers in the area of optoelectronics owing to their superior properties. The current work focuses on the preparation of symmetric interdigitated Au electrodes on Ta2O5/GaN heterojunction and to check its functioning as a photosensor in UV region. The impact of post-annealing procedure on the bandgap, crystalline quality, surface morphology and chemical composition has been investigated using UV-VIS, XRD, AFM and XPS techniques, respectively. The evaluated optical bandgaps from the Tauc's plots for the Ta2O5 films ranging from 4.52 eV to 4.92 eV. XRD analysis showed the formation of an orthorhombic phase after post-annealing temperature of 700 °C. The post-annealed Ta2O5 film surface morphology comprises prearranged atomic clusters with spherical shapes. The XPS exploration revealed the occurrence of the Ta5+ state and confirmed the formation of Ta2O5 phase. Photodetection parameters of the designed Au/Ta2O5/GaN MIS BB PDs are studied using I–V, responsivity and temporal responses as a function of the post-annealing process. At 0 V bias, with the illumination of 310 nm UV light, the 800 °C post-annealed MIS PD device exhibited peak responsivity of 212 mA/W, external quantum efficiency (EQE) of 86.8 % and detectivity of 1.5 × 1013 Jones. Further, under self-driven mode with 350 nm light illumination, the 800 °C post-annealed UV PD device generated faster rise and fall times of 90 ms and 790 ms, respectively. The post-annealed Au/Ta2O5/GaN heterostructure PD device demonstrates improved photoresponsivity, EQE and rise/fall times compared with the as-deposited PD device. This remarkable improvement in the photodetection performance is attributed to the best band configuration of the Ta2O5/GaN heterostructure because of substantial post-annealing process and facilitating broadband absorption from UV-C to A region with quicker generation, separation and transportation of photogenerated charge carriers. Consequently, the current research work emphasizes the significance of the combination of UV sensing Ta2O5 high-k oxide and n-GaN materials to serve the future necessities of the photodetection technology under self-driven mode i.e., without any external bias.