Transition of photoconductive and photovoltaic operation modes in amorphous Ga ₂ O ₃ -based solar-blind detectors tuned by oxygen vacancies

Abstract

We report on the transition of photovoltaic and photoconductive operation modes of the amorphous Ga 2 O 3 -based solar-blind photodetectors in metal-semiconductor-metal (MSM) configurations. The conversion from Ohmic to Schottky contacts at Ti/Ga 2 O 3 interface is realized by tuning the conductivity of amorphous Ga 2 O 3 films with delicate control of oxygen flux in the sputtering process. The abundant donor-like oxygen vacancies distributed near the Ti/Ga 2 O 3 interface fascinate the tunneling process across the barrier and result in the formation of Ohmic contacts. As a consequence, the serious sub-gap absorption and persistent photoconductivity (PPC) effect degrades the performance of the photoconductive detectors. In contrast, the photovoltaic device with a Schottky contact exhibits an ultra-low dark current less than 1 pA, a high detectivity of 9.82×10 12 cm•Hz 1/2 •W −1 , a fast response time of 243.9 µs, and a high ultraviolet C (UVC)-toultraviolet A (UVA) rejection ratio of 10 3 . The promoting performance is attributed primarily to the reduction of the subgap states and the resultant suppression of PPC effect. With simple architecture, low fabrication cost, and easy fusion with modern high-speed integrated circuitry, these results provide a cost-effective way to realize high performance solar-blind photodetectors towards versatile practical applications.

Anion Engineering Enhanced Response Speed and Tunable Spectral Responsivity in Gallium-Oxynitrides-Based Ultraviolet Photodetectors

“…The only altered processing condition was the nitrogen flux, which was 0, 10, 40, and 120 sccm, and the resultant Ga 2 O 3 and GaON films are labeled as S0, S1, S2, and S3, respectively. According to our previous study, no obvious changes were observed in growth rate and the film thickness is about 125 nm for all samples . The RT-sputtered Ga 2 O 3 and GaON are in typical amorphous states, as evidenced by the characterization of the grazing incidence X-ray diffraction (GIXRD) spectra in Figure a, where no diffraction peaks related to Ga 2 O 3 are observed.…”

“…The amorphous Ga 2 O 3 detector (S0) exhibits a peak photoresponsivity of 10.35 A/W at the energy position of 4.95 eV with a sharp cutoff edge at 4.35 eV. The corresponding external quantum efficiency is as high as 5260%, which is a typical sign of a persistent photoconductivity effect mediated by a minority-carrier trapping effect as reported in most of Ga 2 O 3 PDs. − With nitrogen incorporation, the photoresponse spectrum for sample S1 exhibits a remarkable reduction in photoresponsivity with an external quantum efficiency (EQE) of about 28%, which is a result of the suppression of the PPC trapping effect due to the reduction of V O and the increased recombination probability induced by nitrogen. A higher nitrogen composition in nitrogen-rich GaON leads toa quite low EQE (even less than 1%), which is resulted from the abundant recombination centers with subgap DOS near VBM .…”

“…Gallium oxide (Ga 2 O 3 ) is a promising candidate for developing solar-blind photodetectors (SBPDs) due to its intrinsic solar blindness with a desirable bandgap of about 4.8 eV, and high resistance against radiation . To date, high efficient SBPDs based on Ga 2 O 3 in various forms of bulk crystals, epitaxial films, nanostructures, and heterostructures have been demonstrated. − In particular, amorphous Ga 2 O 3 was proven to deliver high performance SBPDs and X-ray detectors due to its unique advantages of low-thermal-budget synthesis on flexible substrates and easy fusion with modern high-speed integrated circuitry. − Although high deep-UV (DUV) responsivity could be simply achieved, the response time, a key figure-of-merit for Ga 2 O 3 detectors, was degraded . The unexpected photoconductive gains with the sacrificed slow response speed is resulted from the persistent photoconductivity (PPC) effect induced by the trapping effect involved in oxygen vacancies (V O ) that are abundant in nonstoichiometric Ga 2 O 3 films. − Therefore, the overall performance of the reported amorphous Ga 2 O 3 photodetectors is still far from practical applications.…”

Recent Progress of Deep Ultraviolet Photodetectors using Amorphous Gallium Oxide Thin Films

“…[ 29 ] Zhang et al reported the conversion of Ti/a‐Ga 2 O 3 contact from ohmic to Schottky by tuning the conductivity of a‐Ga 2 O 3 films with the help of a delicate control of oxygen flux during the sputtering process. [ 44 ] Kikuchi et al investigated the electrical and optical properties of a‐Ga 2 O 3 /Cu(In,Ga)Se 2 (CIGS) heterojunction photodiodes where gallium oxide layer is used as a hole‐blocking layer and buffer layer. The oxygen partial pressure during Ga 2 O 3 deposition was optimized to minimize the dark current.…”

“…Zhang et al demonstrated a conversion behavior from ohmic to Schottky contacts at Ti/Ga 2 O 3 interface by regulating the conductivity of a‐Ga 2 O 3 films with delicate control of oxygen flux in the RF‐sputtering process. [ 44 ] For a‐Ga 2 O 3 film deposited without oxygen, abundant donor‐like V O defects near the metal‐Ga 2 O 3 interface facilitated the tunneling process across the barrier, resulting in the contact conversion from Schottky to ohmic, which elevated the photocurrent and dark current simultaneously but degraded the light‐to‐dark ratio. On the contrary, Vu et al showed a different result with a‐Ga 2 O 3 film grown by PLD at 250 °C with a modulation of various oxygen partial pressures from 0 to 50 mTorr during the deposition process.…”