重庆师范大学李万俊教授团队（宽带隙半导体材料与器件团队）在新型光电化学型自供电光电探测器（PEC-PD）研究中取得进展。该团队通过采用低成本氧空位调控的非晶态Ga2O3薄膜，实现了非晶态Ga2O3薄膜光电探测器中响应度和响应速度的同时提升，阐明了自供电PEC-PD中的载流子动力学，揭示了瞬态光电流尖峰与氧空位缺陷浓度之间的显著正相关关系。此外，团队还探索了自供电光电化学型光电探测器阵列在日盲水下成像中的潜在应用。相关成果以"Balancing Carrier Dynamics in Oxygen-Vacancy-Tuned Amorphous Ga2O3 Thin-Film Self-Powered Photoelectrochemical-type Solar-Blind Photodetector Arrays for Underwater Imaging"为题发表在《Advanced Science》杂志上。团队研究生丁科为第一作者，李万俊教授为通讯作者。
水下成像技术对于海洋探索与侦察任务至关重要，因此，研发具备高灵敏度、迅速响应能力和低成本优势的光电探测器（PDs）显得尤为迫切。在这一背景下，新型光电化学光电探测器（PEC-PDs）凭借其独特的优势脱颖而出，特别适用于水下环境，因为它们无需复杂的耐腐蚀封装和光刻工艺，即可直接置于电解质中工作。Ga2O3材料因其卓越的化学稳定性、自然形成的日盲光敏范围，以及避免复杂合金化工艺的需求，而备受瞩目。在前期工作中，团队研发的非晶态Ga2O3基PEC-PDs不仅展现出与晶相Ga2O3探测器相媲美的优异性能，更凭借其出色的柔韧性，为光电探测器领域注入了新的活力，预示着非晶态Ga2O3基PEC-PDs在未来水下探测应用中拥有巨大的潜力和广阔的应用前景（Journal of Materials Chemistry C, 2021, 9:10354；Applied Surface Science, 2023, 624: 157149；Advanced Optical Materials, 2024, 2400116）。然而，关于非晶态Ga2O3基PEC-PDs的研究仍面临以下挑战：
1. 响应度和响应速度不可兼得：传统光电探测器在追求高响应度与快速响应速度之间一直面临困境。而对于自供电PEC-PDs而言，其独特的固液界面引入了更为复杂的载流子动力学机制。在实验中，如何精妙地平衡这些动力学过程，以实现响应度与响应速度的同时提升，仍然是一个极具挑战性的难题。
2. 瞬态光电流尖峰的机制：光电探测器中出现的瞬态光电流尖峰现象，尤其是在自供电PEC-PD中更为显著，已吸引了广泛的科研关注。然而，关于这一现象的潜在机制，目前学术界仍存在诸多争议。深入研究和揭示这一机制，对于更加全面地理解自供电PEC-PD中的载流子动力学过程具有至关重要的意义。
针对这些问题，本研究通过采用低成本氧空位调控的非晶态Ga2O3薄膜，实现了非晶态Ga2O3薄膜光电探测器中响应度和响应速度的同时提升。阐明了自供电PEC-PD中的载流子动力学，揭示了瞬态光电流尖峰与氧空位缺陷浓度之间的显著正相关关系。此外，团队还探索了自供电光电化学型光电探测器阵列在日盲水下成像中的潜在应用。具体发现如下：
1. 氧空位介导的载流子动力学：虽然Ga2O3薄膜中氧空位增强了电催化反应、光电压并降低了界面转移电阻，这对PEC过程是有益的，但它们也导致了严重的载流子复合和陷阱效应，从而导致较低的响应度和较慢的响应速度。通过调节氧空位含量，可以在电催化反应、电荷转移、载流子复合和陷阱之间取得平衡，从而实现响应度和响应速度的同时提升。
2. 瞬态光电流的机制：观察到瞬态光电流尖峰与氧空位含量之间存在显著的正相关关系。从瞬态光电流中提取的空穴传输效率（HTE）随着氧空位的减少而增加，这为瞬态光电流起源于氧空位介导的间接复合提供了重要证据。
3. 日盲水下成像：优化后的PEC-PD表现出卓越的性能，实现了33.75 mA/W的响应度和12.8 ms（上升时间）及31.3 ms（衰减时间）的响应时间，优于绝大多数同类器件。此外，利用自供电PEC-PD阵列构建的日盲水下成像模块，在海水（来自渤海湾）中展现了清晰的成像能力。这项工作为开发低成本、高性能的非晶态Ga2O3薄膜基PEC-PD用于先进水下成像技术提供了参考。
Figure 1. Material Characterizations. a) Cross sectional SEM image and b) Line-scan EDS mapping of the Ga2O3 film. c) Dependence of film growth rate on oxygen flow. d) XRD patterns, e) Raman scattering spectra, and f) Plot of (𝛼h𝜈)2 versus h𝜈 for Ga2O3 films. g) XPS Ga 2p3/2 core-level spectra and h) EPR spectra of S0.0, S0.6, and S1.0. i) VO concentration as a function of oxygen flow. Models of amorphous Ga2O3 with different VO concentrations can be found in Note S1 (Supporting Information).
Figure 2. Self-Powered Photodetection Performance of the PEC-PDs. a) Schematic illustration of the fabrication process for a-Ga2O3 film photoanodes. b) Schematic diagram of a typical PEC system used for evaluating the photoresponse behaviors of the a-Ga2O3 PEC-PDs. c) Dark currents and d) photoresponse behavior of a-Ga2O3 PEC-PDs with different oxygen flow. e) PDCR and responsivity as functions of oxygen flow at 0 V. f) i–t curves normalized to the steady-state photocurrent. g) 𝜏r and 𝜏d as functions of oxygen flow. h) Comparison of the characterization parameters of self-powered a-Ga2O3 PEC-PDs with other Ga2O3-based PEC-PDs. Detailed comparisons are listed in Table S1, (Supporting Information). i) Long-term stability tests in Na2SO4 electrolyte and seawater (sourced from Bohai Bay).
Figure 3. Charge-Transfer Properties of PEC-PDs. a–c) Photovoltage and photocurrent analyses of S0.0, S0.6, and S1.0. d) ΔOCP-1 and ΔOCP-2/ΔOCP-1 of different devices. e,f) Nyquist plots and Bode phase curves of S0.0, S0.6, and S1.0. g) Schematic diagram of charge transfer in self-powered a-Ga2O3 PEC-PDs with different VO defects.
Figure 4. Mechanism of Transient Spike Currents. a) Typical transient photocurrent behavior and b) schematic representation of carrier dynamics in transient currents of a-Ga2O3 PEC-PDs. c) i–t curves normalized to the steady-state photocurrent. d) HME and CQR as functions of oxygen flow. e) Photoresponse of S0.6 under illumination at 254 nm with various light power intensities from 10 to 400 μWcm−2. (f) HME and CQR of S0.6 as functions of light power intensities.
Figure 5. Proof-of-Concept Demonstration of Solar-Blind Underwater Imaging. a) Schematic of the solar-blind underwater imaging system with a-Ga2O3 PEC-PD arrays. b–d) 3D current mapping of a-Ga2O3 PEC-PD arrays irradiated in the dark, and 254 nm with 100 and 400 μWcm−2 light intensity, respectively. e,f) Underwater imaging based on a-Ga2O3 PEC-PD arrays, clearly distinguishing the shapes of the characters “C”, “N”, and “U”.
论文信息：
Ke Ding, Hong Zhang, Jili Jiang, Jiangshuai Luo, Rouling Wu, Lijuan Ye, Yan Tang, Di Pang, Honglin Li and Wanjun Li*. Balancing Carrier Dynamics in Oxygen-Vacancy-Tuned Amorphous Ga2O3 Thin-Film Self-Powered Photoelectrochemical-type Solar-Blind Photodetector Arrays for Underwater Imaging. Advanced Science, 2024, 2407822.
论文链接：
https://doi.org/10.1002/advs.202407822.
重庆师范大学宽禁带半导体材料与器件团队
https://www.x-mol.com/groups/li_wanjun
