Enhancing broadband response of hot-electron photodetectors by Au/TiO2 composite nanostructure
-
摘要: 宽谱响应光电探测器在图像传感和光通信等领域应用前景广阔。金属微纳结构通过激发表面等离激元共振效应可高效产生热载流子,将它们与宽带隙半导体构成异质结构,便可利用热载流子开发出低成本宽谱响应光电探测器。研究设计了一种基于Au/TiO2复合纳米结构的热电子光电探测器。其中TiO2层经退火后形成尺度约为百纳米的凹凸结构,Au纳米颗粒层与用作电极的保形Au膜共同组成了激发表面等离激元共振的纳米结构。由于Au/TiO2复合纳米结构的协同作用,该器件在400~900 nm范围内具有宽谱光吸收性能,器件的平均光吸收效率为33.84%。在此基础上,该器件能够探测TiO2本征吸收波段以外的入射光子。例如,在600 nm波长处,器件的响应率为9.67 μA/W,线性动态范围为60 dB,器件的上升/下降响应速度分别为1.6 ms和1.5 ms。此外,利用有限元法进行了仿真计算,通过电场分布图验证了Au/TiO2复合纳米结构中所激发的丰富表面等离激元共振效应是其实现宽谱高效探测的原因所在。Abstract:
Objective Hot electron photodetectors (HEPDs) with wide spectrum responses are promising in the fields of image sensors and optical communications, etc. Metallic micro/nano-structures can efficiently generate hot carriers by exciting surface plasmons. It is helpful to realize low-cost and wide-spectrum response photodetectors when the heterostructures form by combining metallic micro/nano-structures with wide bandgap semiconductors. This approach can also be applied to improve the performance of HEPDs made of other semiconductors. This work contributes to the development of advanced plasmonic devices. Methods During the fabrication, the wet-cleaned FTO glass substrates were first subjected to the surface plasma treatment for increasing the work function of FTO substrates. Then, TiO2 and Au films were prepared by radio frequency (RF) and direct current (DC) magnetron sputtering, respectively. In detail, a TiO2 layer with a thickness of 20 nm was deposited onto the FTO substrate, followed by the deposition of an ultrathin Au film with its thickness varying from 2 nm to 8 nm. Then, the as-prepared multiplayer samples were annealed in air at 500 °C. The annealing process could, simultaneously, transform the ultrathin Au film into a layer of Au NPs, and transform the amorphous TiO2 film into its polycrystalline anatase film structure with a rough profile. After that, another thin Au film was deposited onto the annealed samples by DC magnetron sputtering. Here, the thin Au film can act as the transparent electrode with its thickness fixed to 20 nm. Results and Discussions The proposed hybrid plasmonic nanostructure based HEPD has an architecture as shown in Figure 1. Here, the TiO2 layer formed a concave-convex nanostructure with a scale of about 100 nm after annealing process, the nanostructure constructed by the Au nanoparticle layer and the conformal Au film used as electrode is for exciting surface plasmons. With the assistance of the Au/TiO2 composite nanostructure, the device has a wide spectrum absorption in the range of 400 nm to 900 nm, and the average absorption efficiency is 33.84%. Therefore, the proposed device can detect the incident photons outside the intrinsic absorption band of TiO2. The responsivity and linear dynamic range of the device under the wavelength of 600 nm separately are 9.67 μA/W and 60 dB (Fig.2). Besides, the corresponding rise/fall response speed are 1.6 ms and 1.5 ms respectively. (Fig.3). The finite element method is also used for simulation calculation, and the electric field distribution diagrams verify that the rich surface plasmon resonances excited in the Au/TiO2 composite nanostructure, which is the reason for realizing the wide spectrum and high efficiency detection (Fig.5). Conclusions In summary, we demonstrated a TiO2-based HEPD by incorporating a hybrid plasmonic nanostructure made of Au NPs together with a conformal Au film. Different from other similar approaches that were designed for high-efficiency hydrogen generation in the photocatalysts, a hybrid plasma nanostructure was used in photodetectors for realizing wide spectrum response. With the structural diversity of the hybrid plasmonic nanostructure, different surface plasmon resonances were excited, so that the device can respond to incident photons in a broadband wavelength range, covering UV-visible-NIR. The method of constructing hybrid plasmonic nanostructures has a guidance in developing high-performance optoelectronic devices. -
Key words:
- photodetectors /
- surface plasmon resonance /
- metal nanostructure /
- hot-electrons /
- wide spectrum
-
图 1 (a) 基于Au/TiO2复合纳米结构的热电子光电探测器结构示意图;(b) 器件中各功能层的能级结构图;(c) 器件的SEM侧视图;(d) 器件的SEM俯视图
Figure 1. (a) Schematic diagram of the proposed HEPD based on Au/TiO2 composite nanostructure; (b) Structural diagram of the energy levels of the materials used in the proposed HEPD; (c), (d) Cross-sectional and top-view SEM images of the proposed device respectively
2 (a) 具有不同TiO2膜厚度(tTiO2)器件的暗态I-V曲线图。器件在偏压0 V、tTiO2 = 20 nm时的性能表征图:(b) 光吸收谱;(c) 外量子效率;(d) 响应率;(e) 线性动态范围。(f) 热电子在Au/TiO2肖特基结界面处的产生及传输示意图
2. (a) I-V curves of devices with different thicknesses of TiO2 film (tTiO2) in the dark state. The response characteristics of the device with tTiO2 = 20 nm under 0 V bias: (b) Absorption spectra; (c) External quantum efficiency (EQE); (d) Responsivity; (e) Linear dynamic range. (f) Schematic diagram of hot electron generation and transfer process over the Au/TiO2 Schottky barrier
图 4 具有不同TiO2膜厚度 (tTiO2) 和顶层保形Au膜厚度 (tAu) 器件的响应性能对比:(a)、(c) 瞬态光电流的对比图;(b)、(d) 光电流与其对应的平均光吸收效率对比曲线图
Figure 4. Comparison of response performance of devices with different tTiO2 and tAu respectively: (a), (c) Transient photocurrents; (b), (d) Photocurrents and the corresponding average light absorption efficiencies
图 5 (a) 具有不同 tn-Au 器件的瞬态光电流对比图;(b) 随tn-Au变化的光电流及平均光吸收效率曲线对比图。归一化电场分布图(|E|2):(c) tn-Au = 4 nm时的最优器件及(d) 参比器件
Figure 5. (a) Comparison of the transient photocurrents for the devices with different tn-Au; (b) Comparison diagram between the photocurrents and average absorption efficiencies of the devices with different tn-Au. The normalized electric field distributions (|E|2): (c) The optimal device with tn-Au = 4 nm and (d) the reference device
图 6 具有Au-film、Ag-film、Cu-film顶层保形金属膜器件的响应性能对比:(a) 瞬态光电流;(b) 光电流与其对应的平均光吸收效率
Figure 6. Comparison of response performance of devices with top conformal metal films of Au-film, Ag-film and Cu-film: (a) Transient photocurrents; (b) Photocurrents and the corresponding average light absorption efficiencies
-
[1] Shao W, Yang Q, Zhang C, et al. Planar dual-cavity hot-electron photodetectors [J]. Nanoscale, 2019, 11(3): 1396-1402. doi: 10.1039/C8NR05369C [2] Knight M W, Sobhani H, Nordlander P, et al. Photodetection with active optical antennas [J]. Science, 2011, 332(6030): 702-704. doi: 10.1126/science.1203056 [3] Wang L, He S J, Wang K Y, et al. Dual-plasmonic Au/graphene/Au-enhanced ultrafast, broadband, self-driven silicon Schottky photodetector [J]. Nanotechnology, 2018, 29(50): 505203. doi: 10.1088/1361-6528/aae360 [4] Yang Z, Du K, Wang H, et al. Near-infrared photodetection with plasmon-induced hot electrons using silicon nanopillar array structure [J]. Nanotechnology, 2019, 30(7): 075204. doi: 10.1088/1361-6528/aaf4a6 [5] Qiu Kaifang, Zhai Aiping, Wang Wenyan, et al. Research progress on surface plasmon hot-carrier photodetectors [J]. Semiconductor Technology, 2020, 45(3): 169-178. (in Chinese) [6] He Weidi, Su Dan, Wang Shanjiang, et al. Progress of surface plasmon nanostructure enhanced photodetector (Invited) [J]. Infrared and Laser Engineering, 2021, 50(1): 20211014. (in Chinese) [7] Sun R N, Peng K Q, Hu B, et al. Plasmon enhanced broadband optical absorption in ultrathin silicon nanobowl array for photoactive devices applications [J]. Applied Physics Letters, 2015, 107(1): 013107. [8] Wu B H, Liu W T, Chen T Y, et al. Plasmon-enhanced photocatalytic hydrogen production on Au/TiO2 hybrid nanocrystal arrays [J]. Nano Energy, 2016, 27: 412-419. doi: 10.1016/j.nanoen.2016.07.029 [9] Yan Xianyong, Zhai Aiping, Shi Linlin, et al. Research progress on solar water splitting based on hot carrier effect of surface plasmon polaritons [J]. Semiconductor Technology, 2021, 46(8): 581-590, 616. (in Chinese) [10] Ishii S, Shinde S L, Nagao T. Nonmetallic materials for plasmonic hot carrier excitation [J]. Advanced Optical Materials, 2018, 7(1): 00603. [11] Jang Y J, Chung K, Lee J S, et al. Plasmonic hot carriers imaging: promise and outlook [J]. ACS Phontonics, 2018, 5(12): 4711-4723. [12] Ho Y-L, Tai Y-H, Clark J K, et al. Plasmonic hot-carriers in channel-coupled nanogap structure for metal–semiconductor barrier modulation and spectral-selective plasmonic monitoring [J]. ACS Photonics, 2018, 5(7): 2617-2623. doi: 10.1021/acsphotonics.7b01307 [13] Li W, Valentine J G. Harvesting the loss: Surface plasmon-based hot electron photodetection [J]. Nanophotonics, 2017, 6(1): 177-191. doi: 10.1515/nanoph-2015-0154 [14] Zayats A V, Maier S. Hot-electron effects in plasmonics and plasmonic materials [J]. Advanced Optical Materials, 2017, 5(15): 1700508. [15] Kösemen A, Alpaslan Kösemen Z, Canimkubey B, et al. Fe doped TiO2 thin film as electron selective layer for inverted solar cells [J]. Solar Energy, 2016, 132: 511-517. doi: 10.1016/j.solener.2016.03.049 [16] Wang Qilong, Li Yupei, Zhai Yusheng, et al. Progress of surface plasmon enhanced near-infrared photodetector based on metal/Si Schottky heterojunction [J]. Infrared and Laser Engineering, 2019, 48(2): 0203002. (in Chinese) [17] Zhang C, Qian Q, Qin L, et al. Broadband light harvesting for highly efficient hot-electron application based on conformal metallic nanorod arrays [J]. ACS Photonics, 2018, 5(12): 5079-5085. doi: 10.1021/acsphotonics.8b01389 [18] Tanzid M, Ahmadivand A, Zhang R, et al. Combining plasmonic hot carrier generation with free carrier absorption for high-performance near-infrared silicon-based photodetection [J]. ACS Photonics, 2018, 5(9): 3472-3477. doi: 10.1021/acsphotonics.8b00623 [19] Mirzaee S M A, Lebel O, Nunzi J M. Simple unbiased hot-electron polarization-sensitive near-infrared photodetector [J]. ACS Appl Mater Interfaces, 2018, 10(14): 11862-11871. [20] Luo X, Zhao F, Liang Y, et al. Facile nanogold-perovskite enabling ultrasensitive flexible broadband photodetector with pW scale detection limit [J]. Advanced Optical Materials, 2018, 6(23): 1800996. [21] Gao Linhua, Cui Yanxia, Liang Qiangbing, et al. Research progress in metal-inorganic semiconductor-metal photodetectors [J]. Infrared and Laser Engineering, 2020, 49(8): 20201025. (in Chinese) [22] Wu K, Zhan Y, Wu S, et al. Surface-plasmon enhanced photodetection at communication band based on hot electrons [J]. Journal of Applied Physics, 2015, 118(6): 063101. doi: 10.1063/1.4928133 [23] Fang Z, Liu Z, Wang Y, et al. Graphene-antenna sandwich photodetector [J]. Nano Letters, 2012, 12(7): 3808-3813. doi: 10.1021/nl301774e [24] Zhang C, Wu K, Ling B, et al. Conformal TCO-semiconductor-metal nanowire array for narrowband and polarization-insensitive hot-electron photodetection application [J]. Journal of Photonics for Energy, 2016, 6(4): 042502. doi: 10.1117/1.JPE.6.042502 [25] Nusir A I, Abbey G P, Hill A M, et al. Hot electrons in microscale thin-film Schottky barriers for enhancing near-infrared detection [J]. IEEE Photonics Technology Letters, 2016, 28(20): 2241-2244. doi: 10.1109/LPT.2016.2591261 [26] Nazirzadeh M A, Atar F B, Turgut B B, et al. Random sized plasmonic nanoantennas on Silicon for low-cost broad-band near-infrared photodetection [J]. Sci Rep, 2014, 4: 7103. [27] Qi Z, Zhai Y, Wen L, et al. Au nanoparticle-decorated silicon pyramids for plasmon-enhanced hot electron near-infrared photodetection [J]. Nanotechnology, 2017, 28(27): 275202. doi: 10.1088/1361-6528/aa74a3 [28] Besteiro L V, Kong X T, Wang Z, et al. Understanding hot-electron generation and plasmon relaxation in metal nanocrystals: quantum and classical mechanisms [J]. ACS Photonics, 2017, 4(11): 2759-2781. doi: 10.1021/acsphotonics.7b00751 [29] Ratchford D C, Dunkelberger A D, Vurgaftman I, et al. Quantification of efficient plasmonic hot-electron injection in gold nanoparticle-TiO2 films [J]. Nano Lett, 2017, 17(10): 6047-6055. doi: 10.1021/acs.nanolett.7b02366 [30] Gundlach L, Ernstorfer R, Willig F. Escape dynamics of photoexcited electrons at catechol: TiO2(110) [J]. Physical Review B, 2006, 74(3): 035324. [31] Tobaldi D, Piccirillo C, Rozman N, et al. Effects of Cu, Zn and Cu-Zn addition on the microstructure and antibacterial and photocatalytic functional properties of Cu-Zn modified TiO2 nano-heterostructures [J]. Journal of Photochemistry Photobiology A: Chemistry, 2016, 330: 44-54. doi: 10.1016/j.jphotochem.2016.07.016 [32] Shinotsuka H, Tanuma S, Powell C J, et al. Calculations of electron inelastic mean free paths. X. data for 41 elemental solids over the 50 eV to 200 keV range with the relativistic full Penn algorithm [J]. Surface and Interface Analysis, 2015, 47(9): 871-888. doi: 10.1002/sia.5789 [33] Fang Y, Jiao Y, Xiong K, et al. Plasmon enhanced internal photoemission in antenna-spacer-mirror based Au/TiO2 nanostructures [J]. Nano Letters, 2015, 15(6): 4059. doi: 10.1021/acs.nanolett.5b01070 [34] Liang F X, Wang J Z, Wang Y, et al. Single-layer graphene/titanium oxide cubic nanorods array/FTO heterojunction for sensitive ultraviolet light detection [J]. Applied Surface Science, 2017, 426: 391-398. doi: 10.1016/j.apsusc.2017.07.051 [35] Hartland G V, Besteiro L V, Johns P, et al. What’s so hot about electrons in metal nanoparticles? [J]. ACS Energy Letters, 2017, 2(7): 1641-1653. doi: 10.1021/acsenergylett.7b00333 [36] Zhang H, Govorov A O. Optical generation of hot plasmonic carriers in metal nanocrystals: The effects of shape and field enhancement [J]. The Journal of Physical Chemistry C, 2014, 118(14): 7606-7614. doi: 10.1021/jp500009k [37] Moskovits M J S. Hot electrons cross boundaries [J]. Science, 2011, 332(6030): 676-677. [38] Shiraishi Y, Yasumoto N, Imai J, et al. Quantum tunneling injection of hot electrons in Au/TiO2 plasmonic photocatalysts [J]. Nanoscale, 2017, 9(24): 8349-8361. doi: 10.1039/C7NR02310C [39] Li Y, Guo Y, Li Y, et al. Fabrication of Cd-doped TiO2 nanorod arrays and photovoltaic property in perovskite solar cell [J]. Electrochimica Acta, 2016, 200: 29-36. doi: 10.1016/j.electacta.2016.03.091