Investigating the role of oxygen and related defects in the self-biased and moderate-biased performance of β-Ga₂O₃ solar-blind photodetectors

Abstract

High-performance, low-cost, self-powered deep-ultraviolet photodetectors (DUV-PDs) are essential for military and civil applications. β-Ga2O3 stands alone among all the solar-blind materials in its suitability for use in next-generation DUV-PDs. However, deep traps by oxygen vacancies critically affect the photogenerated carriers, and hence the photodetector’s final efficiency. Notwithstanding, both a lack of and an excess of oxygen in β-Ga2O3 ultimately lead to leakage channels, carrier scattering and sub-bandgap absorption. However, no studies on the impact of extremes of oxygen (oxygen-poor and oxygen-rich) on β-Ga2O3 photodetector efficiency are available in the literature. Therefore, in the present work, we aim to understand the impact of varied oxygen flow rates from 0% to 4% on material properties and photodetector performance. Photoluminescence, time-resolved photoluminescence (TRPL), x-ray photoelectron spectroscopy and the electrical properties of fabricated photodetectors confirmed the critical role of oxygen in β-Ga2O3. TRPL measurements revealed that β-Ga2O3 with 1% oxygen flow had a reported shortest decay time of nearly 50 ps. A very low dark current of 0.9 pA and a maximum photo-to-dark current of >103 were achieved at zero bias for β-Ga2O3 under optimum oxygen flow. The responsivity, external quantum efficiency, detectivity and dark current for a sample at moderate bias fabricated under optimum oxygen flow were found to be 190.08 A W−1, 9.42 × 104%, 1.22 × 1015 Jones and 21 nA, respectively. Hence, the measurements showed that for better device performance and self-powered response, oxygen concentrations that are neither too low nor too high are needed, and the detailed mechanism behind this is discussed. Comparison of the figures of merit with those of other reported devices in both self-powered and high bias mode reveals the far superior performance of the present device.

Ga2O3/GaN Heterointerface-Based Self-Driven Broad-Band Ultraviolet Photodetectors with High Responsivity

“…The time-resolved photoluminescence (TRPL) spectrum was obtained to determine the decay constants of the Ga 2 O 3 film inset (Figure b). The TRPL data were fitted using the following two-order exponential decay formula R ( t ) = A 1 + B 1 0.25em normale − t / τ 1 + B 2 0.25em normale − t / τ 2 where A 1 is the constant component, τ 1 and τ 2 are relaxation time constants (fast and slow), B 1 and B 2 are constant amplitudes, and t is the time. The τ 1 relates to the fast decay component, commonly attributed to the surface recombination of the carriers.…”

Aqueous‐Printed Ga2O3 Films for High‐Performance Flexible and Heat‐Resistant Deep Ultraviolet Photodetector and Array

“…[ 38,39 ] In spite of the similar element ratios of S350 and S900 (Figure S2, Supporting Information), the following phenomena further support the crystallization process of Ga 2 O 3 in the S900 film during 900 °C annealing, including i) reduction of oxygen vacancies reflected by the decreased ratio of O II /(O I +O II ) (Figure 2c), [ 24,40 ] ii) enhancement of intrinsic ultraviolet emission caused by the recombination of free electrons and self‐trapped holes, iii) suppression of visible‐light (blue and green) emission attributed to the excitation of vacancy and interstitial defects of both oxygen and gallium (Figure 2d), [ 41,42 ] and iv) inhibition of carrier lifetime possibly due to the diminished defect‐induced traps (Figure 2e). [ 43,44 ] These results solidly demonstrate that the printed Ga 2 O 3 film obtains higher crystallinity and the intrinsic defects are significantly reduced during the annealing process. To investigate the optical properties of the samples, the transmission spectra of the S350 and S900 films both display almost 100% transmittance to visible light and strong absorption of DUV range.…”

“…τ 1 and τ 2 represent the fast‐response component and slow‐response component, respectively. The response time (τ r1 /τ r2 ) and decay time (τ d1 /τ d2 ) of the photodetector were calculated to be 0.313/2.894 and 0.026/0.221 s. The great improvement of the response speed of the S900 device should be ascribed to the decrement of the oxygen vacancy‐induced traps, and the increment of the recombination centers formed during the N ‐annealing process, [ 24,44 ] consistent with the results of TRPL spectra. Based on the systematic comparison, the S900 photodetector exhibits an extremely improved comprehensive performance compared to all control devices, demonstrating the superiority of these optimized Ga 2 O 3 films for ultraviolet photodetection.…”

Superflexible, Self-Biased, High-Voltage-Stable, and Seal-Packed Office-Paper Based Gallium-Oxide Photodetector

“…Oxygen gas (1%) was purged over the entire deposition as it ensures the high quality of grown thin film. The experimental details for the same can be found elsewhere . A high quality a-Ga 2 O 3 thin film of thickness nearly ∼250–300 nm was then deposited at room temperature (RT) on top of the electrodes at 100 W RF power confirmed by ellipsometry.…”

“…The experimental details for the same can be found elsewhere. 27 A high quality a-Ga 2 O 3 thin film of thickness nearly ∼250−300 nm was then deposited at room temperature (RT) on top of the electrodes at 100 W RF power confirmed by ellipsometry. The substrate stage was continuously rotated at 11 rpm to ensure a highly uniform film.…”