COMMUNICATION 1700638 (1 of 8) © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advopticalmat.de Trap Assisted Bulk Silicon Photodetector with High Photoconductive Gain, Low Noise, and Fast Response by Ag Hyperdoping Xiaodong Qiu, Xuegong Yu,* Shuai Yuan, Yuhan Gao, Xuemei Liu, Yang Xu, and Deren Yang* DOI: 10.1002/adom.201700638 suffer from high cost, complementary metal–oxide–semiconductor (CMOS) incompatibility, and not being environ- ment friendly. Design and fabrication of a low-cost and CMOS-compatible silicon- based photoconductor is always urgent for current and future optoelectronics applica- tion. Unfortunately, silicon-based photo- conductors usually exhibit a certain degree of latency in the photocurrent fluctuation when light is on or off, usually around 1–10 ms. [13–15] Meanwhile, they also suffer from a very large dark current, due to the extrinsic charge injection under reverse bias voltage, which causes the shot noise, weakens the detection sensitivity, and increases the power wastage. [12,16] Recently, the chalcogen (S, Se, and Te) and some transition metals (Au, Ti, etc.) hyperdoping in silicon has been recognized to be a potential for the fab- rication of silicon-based photodetec- tors. [3,4,17–31] It has been reported that the chalcogen hyperdoped silicon photodetector can exhibit a high photoconductive gain under illumination while pre- serve a diode-rectifying effect in the dark. [24–26,29–31] This provides a novel path to the silicon-based photoconductors with a low noise and a high detect sensitivity. It was reported that the charge carrier trap states may play an essential role in the enhanced photoresponse. [24] However, this phe- nomenon has not yet been reported in the transition metal hyperdoped silicon photodetectors, and the related mechanism and its operating principle for this type of silicon photo- conductors are still open for question. Meanwhile, theoretical calculations suggest that chalcogen dopant hyperdoping in silicon is not the best choice for the fabrication of photo- conductors. [32,33] The silver (Ag) hyperdoping in silicon has a relatively higher optical figure of merit (v, defined by the ratio of carrier lifetime to transmit time), which is expected to have stronger potential in the optoelectronic application. [32,33] However, this interestingly theoretical prediction is still lack of the verification of related experiments. Here, we report a highly sensitive and room-temperature operated bulk silicon photodetector based on Ag hyperdoped silicon (Si:Ag). The Si:Ag samples were prepared by thermal evaporation deposition of Ag films and subsequent femto- second pulsed laser melting (fs-PLM). A large density of Silicon-based photoconductors, with their low cost, high sensitivity, and complementary metal–oxide–semiconductor (CMOS) compatibility, have great potential for high-resolution imaging, light-activated switching, and single- photon counting. However, they usually suffer from a large dark leakage current and a long response time, which greatly limits their applications. Here, a high- performance bulk silicon photodetector is fabricated working at room tempera- ture with a broad spectral response range from 300 to 1200 nm through silver (Ag) hyperdoping. The detector shows a low dark current of 3.8 × 10 -7 A cm -2 and a high external quantum efficiency of 266.0% for 800 nm at -1 V reverse bias, indicating a photoconductive gain. Moreover, the Si:Ag photodetector has a very low noise and a high detectivity (≈1.84 × 10 12 Jones at -1 V), and meanwhile exhibits a rapid response speed with the rise time of 12.5 μs and fall time of 15.9 μs. By combining with the deep level transient spectrum measurements, it is believed that the operating mechanism of the detector is based on the electron traps with an average energy level of E c – 0.28 eV induced by the Ag hyperdoping. These results are of significance for the fabri- cation of silicon-based photodetectors with high performances. X. Qiu, Prof. X. Yu, Dr. S. Yuan, Y. Gao, Prof. D. Yang State Key Laboratory of Silicon Materials and School of Materials Science and Engineering Zhejiang University Hangzhou, Zhejiang 310027, China E-mail: yuxuegong@zju.edu.cn; mseyang@zju.edu.cn X. Liu, Prof. Y. Xu College of Information Science and Electronic Engineering Zhejiang University Hangzhou, Zhejiang 310027, China Silicon Photodetectors Photodetectors, which can achieve the conversion of optical to electrical signals, have been widely used in a variety of fields, including telecommunication, environmental sensing, biomed- icine, monitoring, security equipments, etc. [1–8] For an effective photodetector, some stringent requirements must be satisfied, e.g., high responsivity, low noise, and high response speed at its working wavelength range. Photoconductor is an attractive candidate for highly sensitive photodetectors due to its ability to trigger intrinsic photocurrent amplification, and therefore they have been adopted in high resolution imaging, fiber-optical communication, and single photon counting. [9–12] Commer- cially available photoconductors to date are mostly fabricated with CdS, PbS, and CdTe. However, these materials generally Adv. 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