Key Takeaways & Executive Findings
- •• • Dark current as low as 30.9 fA at the lowest oxygen vacancy content enables ultra-low-noise operation, critical for photon-starved astronomical and medical imaging where signal-to-noise ratio dictates detection limits. • • SBUV responsivity of 237 A W−1 and photo-to-dark current ratio of 8.7 × 10^8 under 254 nm illumination demonstrate high sensitivity and strong solar-blind/visible rejection, essential for flame detection and UV astronomy. • • X-ray sensitivity of 10,736 μC cm−2 Gy_air−1 is 477 times higher than conventional a-Se detectors, offering a pathway to lower patient dose in medical radiography and improved contrast in non-destructive testing. • • Response speed (τr1/τd1) of 155/34 ms under SBUV and stable performance under long-term X-ray irradiation indicate sufficient temporal resolution for imaging applications and robust operational lifetime.
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Abstract
β-Ga2O3 metal-semiconductor-metal photodetectors were fabricated on MOCVD-grown films with controlled oxygen vacancy content via the Foxy/FTEGa precursor ratio. Increasing Foxy/FTEGa improved crystallinity and reduced oxygen vacancy concentration. The optimal device exhibited a dark current of 30.9 fA, a photo-to-dark current ratio of 8.7 × 10^8, and a responsivity of 237 A W−1 under 254 nm solar-blind ultraviolet illumination, with rise/decay times of 155/34 ms. Under X-ray irradiation, the detector achieved a sensitivity of 10,736 μC cm−2 Gy_air−1, 477 times higher than conventional a-Se detectors, and maintained stable performance during prolonged X-ray exposure. Energy-band analysis under different photoinjection conditions clarified the distinct roles of oxygen vacancies in SBUV and X-ray photoresponse, linking defect density to responsivity and response speed. These findings provide a mechanistic framework for engineering Ga2O3-based detectors with optimized comprehensive performance for astronomical imaging, medical diagnostics, and harsh-environment applications.
1. Introduction
Wide-bandgap semiconductors such as GaN, SiC, and diamond have been explored for ultraviolet and X-ray detection, yet their performance is often limited by material quality, defect density, and device architecture. β-Ga2O3, with its ~4.9 eV bandgap, intrinsically absorbs solar-blind ultraviolet light and exhibits high X-ray attenuation efficiency, making it a promising candidate for dual-band detection. However, the mechanisms governing SBUV and X-ray photoresponse in Ga2O3 remain poorly understood, particularly the role of oxygen vacancies, which hinders rational device optimization.
Existing Ga2O3 detectors have achieved high responsivity and rejection ratios, but the trade-off between dark current, response speed, and sensitivity under different irradiation conditions persists. This study addresses the bottleneck by systematically modulating oxygen vacancy content through the Foxy/FTEGa ratio during MOCVD growth. By correlating defect density with photoresponse under SBUV and X-ray illumination, the work clarifies the differential roles of oxygen vacancies and provides a design strategy for high-performance, low-noise detectors with stable operation.
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Shunjie Yu, Xiaohu Hou, Yan Liu, Xiaolong Zhao, Shibing Long (2025). High-performance β-Ga2O3 solar-blind UV/X-ray photodetector enhanced by oxygen vacancy modulation. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3495-8
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Frequently Asked Questions
What is the dark current and its impact on detector noise?
The device with the lowest oxygen vacancy content achieved a dark current of 30.9 fA, which is among the lowest reported for Ga2O3 MSM photodetectors. This low dark current directly reduces shot noise and enables high signal-to-noise ratios, critical for detecting weak signals in astronomical and medical imaging.
How does the X-ray sensitivity compare to commercial a-Se detectors?
The X-ray sensitivity of 10,736 μC cm−2 Gy_air−1 is 477 times higher than that of conventional a-Se detectors. This dramatic improvement could allow for lower X-ray doses in medical diagnostics while maintaining image quality, reducing patient exposure.
What are the response times under SBUV illumination?
The rise and decay times (τr1/τd1) are 155 ms and 34 ms, respectively. These values are adequate for many imaging applications but may limit use in high-speed detection scenarios; further optimization of device geometry and defect passivation could improve speed.
How stable is the detector under prolonged X-ray irradiation?
The device maintains stable performance under long-term X-ray irradiation, with no significant degradation reported. This stability is attributed to the high crystal quality and low oxygen vacancy content, which mitigate defect generation and charge trapping.
What is the role of oxygen vacancies in SBUV versus X-ray photoresponse?
Oxygen vacancies act as trap states that influence carrier lifetime and transport. Under SBUV, they primarily affect responsivity and response speed by modulating recombination. Under X-ray, they contribute to gain mechanisms but can also increase dark current. The study shows that minimizing oxygen vacancies enhances both sensitivity and stability.
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