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Whispering gallery modes enhance the near-infrared photoresponse of hourglass-shaped silicon nanowire photodiodes


Silicon photodiodes are widely used in applications that require the measurement of the intensity, colour and position of visible light. Silicon is an attractive material for these systems owing to its low cost, low noise, and easy on-chip integration with read-out electronics. However, silicon cannot effectively be used to detect near-infrared (NIR, at wavelengths of 700–1,000 nm) light and short-wave infrared (SWIR, 1,000–1,700 nm) light because of its bandgap of 1.12 eV, which is equivalent to a wavelength of 1,100 nm. Here, we report silicon photodiodes based on hourglass-shaped silicon nanowires that use whispering-gallery-mode resonances to enhance their photoresponse in the NIR–SWIR region of the spectrum. The upper, inverted nanocone of the nanowires increases absorption probability by extending the dwell time of NIR–SWIR photons via the generation of whispering-gallery-mode resonances, whereas the lower nanocone with its low reflectance reabsorbs the light incident from surrounding nanowires. Our devices exhibit a higher responsivity and external quantum efficiency than existing silicon photodiodes at 700–1,100 nm. Furthermore, the responsivity at 1,000 nm is similar to that of commercial InGaAs photodiodes and light at 1,400 nm can also be detected. Using our devices, we demonstrate a heart-rate measurement system that offers performance comparable to commercial setups.

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Fig. 1: Hourglass-shaped SiNW PD.
Fig. 2: Electrical and optical characteristics of the fabricated PDs.
Fig. 3: Spectral characteristics of the fabricated PDs.
Fig. 4: Optical simulations of the hourglass-shaped SiNW PD.
Fig. 5: Demonstration of a heart-rate measurement system.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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We acknowledge financial support from the Ministry of Science and ICT, Korea, under the ‘ICT Consilience Creative program’ (IITP-2019-2011-1-00783) and ‘Development of highly sensitive Si photodetector and optimization technique of its characterization of Nd:YAG laser’ (grant number 2018-0-01283) supervised by the Institute for Information and communications Technology Promotion (IITP), under the ‘Smart Industrial Energy ICT Convergence Consortium’ (NIPA-C1601-17-1007) supervised by the National IT Industry Promotion Agency (NIPA), and under the ‘Nano·Material Technology Development Program’ (2009-0082580) and ‘Development of high responsivity and high resolution silicon near-infrared sensor for autonomous vehicles using hourglass nanowire resonator structure’ (NRF-2019R1C1C1005692) supervised by the National Research Foundation of Korea (NRF). This work was also supported by MSS & TIPA under ‘Development of mass productive mid-temperature thermoelectric module based on top-down process technology’ (S2714114).

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Authors and Affiliations



K.K. conceived the idea, designed the experiments, fabricated PD devices, analysed the data, and wrote the paper. S.Y. characterized the PD, analysed the data and wrote the paper. M.S. performed the FDTD simulations and wrote the paper. S.L. and H.C. supported fabrication and characterization of devices. M.M. supported the research, provided advice on the experimental work and contributed to manuscript preparation. C.-K.B. supervised the research. All authors discussed the results and commented on the manuscript.

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Correspondence to Chang-Ki Baek.

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Supplementary Information

Supplementary Figures 1–6 and Tables 1–2.

Supplementary Video 1

Demonstration of the heart-rate measurement system.

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Kim, K., Yoon, S., Seo, M. et al. Whispering gallery modes enhance the near-infrared photoresponse of hourglass-shaped silicon nanowire photodiodes. Nat Electron 2, 572–579 (2019).

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