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作为一种新兴的超宽带隙半导体, Ga2O3在开发高性能的日盲紫外光电探测器方面具有独特的优势. 金属-半导体-金属结构因其制备方法简单、集光面积大等优点在Ga2O3日盲紫外光电探测器中得到了广泛的应用. 本文在传统的金属-半导体-金属结构Ga2O3日盲紫外光电探测器的基础上, 利用原子层沉积技术引入高介电性和绝缘性的氧化铪(HfO2)作为绝缘层和钝化层, 制备出带有HfO2插层的金属-绝缘体-半导体结构的Ga2O3日盲紫外光电探测器, 显著降低了暗电流, 提升了光暗电流比, 同时提高了器件的比探测率和响应速度, 为未来Ga2O3在高性能弱光探测器件制备提供了一种新通用策略.
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关键词:
- 氧化镓 /
- 紫外探测 /
- 金属-绝缘体-半导体 /
- 表面钝化
Solar-blind photodetector (PD) converts 200–280 nm ultraviolet (UV) light into electrical signals, thereby expanding application range from security communication to missile or fire alarms detections. As an emerging ultra-wide bandgap semiconductor, gallium oxide (Ga2O3) has sprung to the forefront of solar blind detection activity due to its key attributes, including suitable optical bandgap, convenient growth procedure, highly temperture/chemical/radiation tolerance, and thus becoming a promising candidate to break the current bottleneck of photomultiplier tubes. The Ga2O3-based solar blind PDs based on various architectures have been realized in the past decade, including photoconductive PDs, Schottky barrier PDs, and avalanche PDs. Till now, the metal-semiconductor-metal (MSM) structure has been widely used in developing photoconductive Ga2O3 solar-blind PDs because of its simple preparation method and large light collection area. Unfortunately, despite unremitting efforts, the performance metric of reported MSM-type Ga2O3 solar-blind PDs still lags behind the benchmark of commercial PMTs. Apparently, lack of solution to the problem has greatly hindered further research and practical applications in this field. One effective strategy for further enhancing the device performance such as detectivity, external quantum efficiency (EQE), and light-to-dark ratio heavily relies on blocking the dark current. In this work, high-quality single crystalline β-Ga2O3 with a uniform thickness of 700 nm is grown by using a metal organic chemical vapor deposition (MOCVD) technique. Then atomic layer deposition (ALD) fabricated ultrathin hafnium oxide (HfO2) films ($ \sim $ 10 nm) are introduced as inserted insulators and passivation layers. The 30 nm/100 nm Ti/Au interdigital electrodes (length: 2800 μm, width: 200 μm, spacing: 200 μm, 4 pairs) are fabricated by sputtering on the top of the film as the Ohmic contacts. Taking advantage of its novel dielectric and insulating properties, the leakage current on Ga2O3 thin film can be effectively inhibited by the inserted ultrathin HfO2 layer, and thus further improving the performance of PDs. Compared with simple MSM structured Ga2O3 PD, the resulting metal-insulator-semiconductor (MIS) device significantly reduces dark current, and thus improving specific detectivity, enhancing light-to-dark current ratio, and increasing response speed. These findings advance a significant step toward the suppressing of dark current in MSM structured photoconductive PDs and provide great opportunities for developing high-performance weak UV signal sensing in the future.-
Keywords:
- gallium oxide /
- ultraviolet detection /
- metal-insulator-semiconductor /
- surface passivation
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图 1 光电探测器结构示意图 (a) MSM结构S1; (b) MIS结构S2; (c) MIS-Passivation结构S3
Fig. 1. Schematic diagrams of the photodetector structure: (a) MSM structure S1; (b) MIS structure S2; (c) MIS-passivation structure S3.
图 2 Al2O3衬底上异质外延的β-Ga2O3薄膜的XRD谱图
Fig. 2. XRD patterns of epitaxial growth of β-Ga2O3 film on Al2O3 substrate.
图 3 所制备薄膜的紫外-可见吸收谱图 (a) 不同薄膜的光学吸收特性曲线; (b) (αhν)2与hν关系曲线
Fig. 3. UV-vis absorbance spectrum: (a) Optical absorption characteristics curves of different thin films; (b) the relationship of (αhν)2 and hν.
图 4 在黑暗和254 nm紫外光照条件下, 不同结构β-Ga2O3紫外光电探测器的I-V特性曲线(对数坐标)(插图为引入氧化铪后器件等效电路图)
Fig. 4. I-V curves (logarithmic coordinate) of different devices with and without 254 nm UV light irradiation (Inset is the equivalent circuit of the device after the insertion of HfO2).
图 6 (a) 50 V偏压下, 光电流与入射光功率强度的对应关系; (b) 1000 μW/cm2的254 nm紫外光照射下, 线性动态范围与外部偏置电压的对应关系
Fig. 6. (a) Relationship of photocurrent and light intensity at 50 V bias; (b) linear dynamic range vs. external bias voltage under 254 nm light illumination with an intensity of 1000 μW/cm2.
图 7 在50 V偏置电压下, 三种不同结构器件的性能参数 (a) PDCR, (b) R, (c) EQE和(d) D*随入射光强的变化曲线
Fig. 7. (a) PDCR and (b) R and (c) EQE and (d) D* of the photodetectors replying on the light intensity under 50 V bias voltage.
图 8 入射光强固定在500 μW/cm2, 三种不同结构器件的性能参数(a) PDCR, (b) R, (c) EQE和(d) D*随偏置电压的变化
Fig. 8. (a) PDCR, (b) R, (c) EQE, and (d) D* of the photodetector varies with the bias voltage under 500 μW/cm2 illumination.
图 9 (a)三种不同结构器件S1, S2, S3在20 V偏压下对254 nm紫外光的光响应I-t特征曲线; (b) S1, (c) S2和(d) S3器件上升及下降沿I-t拟合曲线
Fig. 9. (a) Photoresponse of three different structural devices (S1, S2, and S3) under 254 nm light at a 20 V bias; Rise and decay I-t fitting curves of (b) S1, (c) S2, and (d) S3 photodetectors.
图 10 光电探测器在外加偏置电压下的能带结构及载流子转移过程 (a) 黑暗条件下的MSM结构探测器; (b) 254 nm紫外光照下的MSM结构探测器; (c) 黑暗条件下的MIS结构探测器; (d) 254 nm紫外光照下的MIS结构探测器. (e) 钝化前β-Ga2O3薄膜表面状态示意图; (f) 钝化后β-Ga2O3薄膜表面状态示意图
Fig. 10. Band structures and carriers transfer processes of photodetectors under applied bias voltage: (a) MSM photodetector in the dark; (b) MSM photodetector under 254 nm light; (c) MIS photodetector in the dark; (d) MIS photodetector under 254 nm light. The schematic diagrams in (e) and (f) show the surface states of a β-Ga2O3 film before and after passivation, respectively.
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[1] Chen X, Ren F, Gu S, Ye J 2019 Photonics Res. 7 381
Google Scholar
[2] Kan H, Zheng W, Fu C, Lin R, Luo J, Huang F 2020 ACS Appl. Mater. Interfaces 12 6030
Google Scholar
[3] 郭道友, 李培刚, 陈政委, 吴真平, 唐为华 2019 物理学报 68 078501
Google Scholar
Guo D Y, Li P G, Chen Z W, Wu Z P, Tang W H 2019 Acta Phys. Sin. 68 078501
Google Scholar
[4] Qian L X, Wu Z H, Zhang Y Y, Lai P T, Liu X Z, Li Y R 2017 ACS Photonics 4 2203
Google Scholar
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[10] Wang Y, Li H, Cao J, Shen J, Zhang Q, Yang Y, Dong Z, Zhou T, Zhang Y, Tang W, Wu Z 2021 ACS Nano 15 16654
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Google Scholar
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Google Scholar
[30] 李秀华, 张敏, 杨佳, 邢爽, 高悦, 李亚泽, 李思雨, 王崇杰 2022 物理学报 71 048501
Google Scholar
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Google Scholar
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Google Scholar
Zhou S R, Zhang H, Mo H L, Liu H W, Xiong Y Q, Li H L, Kong C Y, Ye L J, Li W J 2021 Acta Phys. Sin. 70 178503
Google Scholar
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