【Member Papers】Doping-Engineered Modulation of Oxygen Vacancy Formation Energy in Gallium Oxide for High-Performance Solar-Blind UV Photodetectors

      Researchers from Hubei University have published a dissertation titled "Doping-Engineered Modulation of Oxygen Vacancy Formation Energy in Gallium Oxide for High-Performance Solar-Blind UV Photodetectors" in Rare Metals.

Background

      Solar-blind ultraviolet photodetectors eliminate visible light interference and play irreplaceable roles in power grid corona detection, fire alarm, UV communication and underwater imaging. β-Ga₂O₃ with intrinsic 4.6–4.9 eV solar-blind bandgap is the ideal candidate material. Intrinsic β-Ga₂O₃ generates massive oxygen vacancy defects during growth. Oxygen vacancies act as shallow donors to raise dark current, and deep traps to capture photocarriers, leading to slow response and blurry imaging. Existing N, Zn, Zr doping methods only slightly reduce defects and fail to simultaneously achieve ultrahigh PDCR, fast response and high detectivity. PLD/ALD equipment costs are high, while sol-gel introduces organic impurities. Low-cost CVD-compatible doping routes are scarce. Previous Mg-doped Ga₂O₃ works only characterize electrical performance without DFT quantitative analysis of vacancy formation energy. No integrated research combining defect suppression, bandgap widening and imaging demonstration has been reported, forming a major gap for industrial low-cost solar-blind photodetectors.

Abstract

      Solar-blind ultraviolet (UV) photodetectors (SBPDs) play a critical role in applications including UV communication and fire warning systems. Gallium oxide (Ga₂O₃) has emerged as a promising material due to its wide bandgap and low cost, but suffers from high dark current and slow response speed caused by oxygen vacancy (V_O) defects. This work proposes a defect engineering strategy using Mg doping to modulate oxygen vacancy formation energy, fabricating Mg-doped β-Ga₂O₃ (β-Ga₂O₃:Mg) thin-film photodetectors via low-cost chemical vapor deposition (CVD). The doping of Mg suppresses the generation of V_O and broadens the bandgap, which significantly improves the photodetection performance. Experimental results demonstrate that Mg doping achieves a 23% reduction in V_O concentration and increases the bandgap from 4.72 to 4.87 eV. The optimized device exhibits a photo to dark current ratio of 10⁶ (compared to 10⁴ for pristine Ga₂O₃), ultralow dark current of 2.67 ×10⁻¹² A at 20 V, detectivity of 1.576 ×10¹⁴ Jones and response times reduced to 14.7 ms (rise)/7 ms (decay) (318.1 ms/187.5 ms for undoped devices). The photodetector successfully demonstrates UV single-point scanning imaging, clearly displaying “H,” “U,” and “I” letter patterns, and maintains stable performance during 1500-second continuous illumination. This work combines defect engineering with low-cost fabrication to provide a cost-effective reliable solution for high-performance SBPDs.

Highlights

      Propose Mg doping defect engineering route based on low-cost CVD to raise oxygen vacancy formation energy and suppress V_Oconcentration by 23%.

      Realize bandgap widening from 4.72 eV to 4.87 eV, obtain PDCR up to 10⁶and ultralow dark current of 2.67 ×10⁻¹² A @ 20 V.

      Shorten rise/decay response time to 14.7 ms / 7 ms, greatly eliminate carrier trapping induced by oxygen vacancy deep defects.

      Complete DFT theoretical verification and single-point UV imaging test, prove practical application potential of Mg-doped Ga₂O₃ SBPD.

Conclusion

      This study employs a simplified CVD approach to fabricate Mg-doped β-Ga₂O₃ thin films and metal-semiconductor-metal ultraviolet photodetectors. The doping of Mg element was found to have a significant inhibitory effect on the oxygen vacancies present in gallium oxide, either directly or indirectly, by experimental methods such as XPS, EPR and Raman. DFT simulations further validate the underlying mechanism: Mg incorporation elevates V_O formation energy, thereby inhibiting V_O defect generation. The fabricated β-Ga₂O₃:Mg photodetectors exhibit exceptional performance metrics: ultralow dark current of 2.67 ×10⁻¹² A at 20 V, high PDCR of approximately 10⁶, rapid response times of 14.7 ms (rise)/7 ms (decay), and D* of 1.576 ×10¹⁴ Jones. Remarkably, these devices maintain stable performance during 1500 s continuous illumination without significant degradation. The successful demonstration of single-point imaging with clear letter pattern recognition (“H,” “U,” “T”) highlights the commercial potential of this technology. In summary, this work advances Ga₂O₃ doping methodologies, achieves an optimal balance between D* and response time, and provides a new technical pathway for optimizing solar-blind UV photodetector performance.

Project Support

      This work was financially supported by the Major Program of Hubei Province (Grant No. 2023BAA009) and the Natural Science Foundation of Hubei Province (Grant No. 2023AFB623).