Key Takeaways & Executive Findings
- •• • At an oxygen vacancy concentration of 38.88%, the Schottky barrier height drops to 0.54 eV, enabling a responsivity of 1880 mA/W; however, this comes at the cost of a degraded photo-to-dark current ratio (PDCR) and slower response speed, limiting its use in high-sensitivity detection applications. • • Reducing the oxygen vacancy concentration to 30% increases the barrier height to 0.70 eV, which suppresses dark current to 28.4 pA and boosts detectivity to 1.44×10^13 Jones and PDCR to 3.42×10^4, making it suitable for low-noise, high-sensitivity deep-UV photodetection. • • The S3 device exhibits a higher conductance of 5.80×10^-8 S and a carrier concentration of 1.97×10^16 cm^-3, but its abundant oxygen vacancies trap electrons, resulting in slower photo-response speed, which is detrimental for high-speed communication and imaging systems. • • The S5 device, with a larger barrier height and wider depletion region, demonstrates superior detection sensitivity (PDCR of 3.42×10^4) and faster response speed, highlighting that barrier height engineering can effectively balance responsivity and detectivity for specific application requirements.
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Abstract
The optimization of device performance through tunable elemental doping is a critical aspect of semiconductor engineering. This study employs plasma-enhanced chemical vapor deposition to fabricate Sn-doped Ga2O3 films with Sn concentrations ranging from 0 to 1.14 at.%. The oxygen vacancy (OII) concentration is found to modulate the conductivity and the atypical Schottky-type junction behavior at the Ti/Sn-Ga2O3 interface, thereby influencing carrier transport and the detection performance of Au/Ti/Sn-Ga2O3/Ti/Au photodetectors. At an OII concentration of 38.88%, the interfacial Schottky barrier height decreases to 0.54 eV, facilitating electron tunneling and yielding a responsivity of 1880 mA/W. Conversely, a reduced OII concentration of 30% reinforces the barrier height to 0.70 eV, restricting dark current to 28.4 pA while improving detectivity to 1.44×10^13 Jones and the photo-to-dark current ratio to 3.42×10^4. These results underscore the trade-off between doping concentration and performance optimization, demonstrating the potential of interface engineering in regulating electronic transport and device performance.
1. Introduction
Gallium oxide (Ga2O3) has emerged as a promising wide-bandgap semiconductor for deep-ultraviolet (DUV) photodetectors due to its high critical breakdown field, excellent transparent conductivity, and superior radiation hardness compared to GaN. Its bandgap of 4.5–5.2 eV enables inherent sensitivity to DUV radiation, making it ideal for applications such as remote sensing of wildland fires, non-line-of-sight communication, ozone hole monitoring, and missile tracking. However, achieving p-type doping in Ga2O3 is challenging due to the difficulty in forming free holes, which limits the design of advanced device structures. n-type doping via higher-valence elements like Sn, Si, Ge, In, W, Mo, and Nb is more feasible, with Sn acting as a donor by substituting for six-fold coordinated Ga (GaVI).
Despite progress in Sn-doped Ga2O3 photodetectors, the trade-off between responsivity and detectivity remains a critical bottleneck. Heavy doping can enhance conductivity but often increases dark current and reduces sensitivity. Light doping, on the other hand, allows precise regulation of material properties and band structures, but the optimal doping concentration and its impact on interfacial barrier height are not fully understood. This study addresses this gap by systematically varying Sn doping concentration (0–1.14 at.%) in Ga2O3 films via plasma-enhanced chemical vapor deposition and investigating the resulting oxygen vacancy concentrations, barrier heights, and photodetector performance. The findings reveal that tailoring the interfacial barrier height through oxygen vacancy engineering can effectively balance responsivity and detectivity, providing a pathway for optimizing DUV photodetectors for specific applications.
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Lili Yang, Shan Li, Muzi Li, Maolin Zhang, Zeng Liu, Zhang Zhang, Weihua Tang (2025). Sn Doping Induced Interfacial Barrier Height Tailoring in Ga2O3 Deep-Ultraviolet Photodetector. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3509-0
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Frequently Asked Questions
What is the trade-off between responsivity and detectivity in Sn-doped Ga2O3 photodetectors, and how does oxygen vacancy concentration influence it?
The trade-off is evident: at high oxygen vacancy concentration (38.88%), the barrier height decreases to 0.54 eV, boosting responsivity to 1880 mA/W but degrading PDCR and response speed. At lower oxygen vacancy concentration (30%), the barrier height increases to 0.70 eV, reducing dark current to 28.4 pA and improving detectivity to 1.44×10^13 Jones and PDCR to 3.42×10^4. Thus, oxygen vacancy concentration directly modulates barrier height and the balance between sensitivity and speed.
How does the Sn doping concentration affect the oxygen vacancy concentration and the resulting device performance?
Sn doping concentration (0–1.14 at.%) influences oxygen vacancy concentration, which in turn modulates the Schottky barrier height at the Ti/Sn-Ga2O3 interface. Higher Sn doping leads to increased oxygen vacancies, lowering the barrier height and enhancing conductivity and responsivity, but at the expense of detectivity and response speed. Lower Sn doping results in fewer oxygen vacancies, higher barrier height, and improved detectivity and PDCR.
What are the failure mechanisms under prolonged UV exposure or electrical stress for these photodetectors?
The study does not explicitly address long-term reliability, but the presence of oxygen vacancies can act as electron traps, leading to persistent photoconductivity and slow response. Under prolonged UV exposure, the accumulation of trapped charges may degrade the barrier height stability and increase dark current over time. Further stress tests are needed to quantify degradation rates.
What are the scalability and cost challenges for fabricating Sn-doped Ga2O3 photodetectors using PECVD?
PECVD is a scalable technique compatible with industrial processes, but precise control of Sn doping at low concentrations (0–1.14 at.%) and oxygen vacancy concentration requires tight process control. The cost of Sn precursors and the need for high-vacuum systems may impact manufacturing costs. However, the use of earth-abundant Sn and the potential for large-area deposition could offset these costs at scale.
How does the performance of these Sn-doped Ga2O3 photodetectors compare to commercial DUV photodetectors based on AlGaN or SiC?
The reported responsivity of 1880 mA/W and detectivity of 1.44×10^13 Jones are competitive with AlGaN-based photodetectors, which typically show responsivities of 100–200 mA/W and detectivities around 10^12 Jones. However, Ga2O3 offers advantages in radiation hardness and potentially lower cost. The PDCR of 3.42×10^4 is also comparable to commercial devices, but response speed may be a limitation due to oxygen vacancy trapping.
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