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Near-unity quantum efficiency of broadband black silicon photodiodes with an induced junction


Ideal photodiodes can detect all incoming photons independently of the wavelength, angle or intensity of the incident light. Present-day photodiodes notably suffer from optical losses and generated charge carriers are often lost via recombination. Here, we demonstrate a device with an external quantum efficiency above 96% over the wavelength range 250–950 nm. Instead of a conventional p–n junction, we use negatively charged alumina to form an inversion layer that generates a collecting junction extending to a depth of 30 µm in n-type silicon with bulk resistivity larger than 10 kΩ cm. We enhance the collection efficiency further by nanostructuring the photodiode surface, which results in higher effective charge density and increased charge-carrier concentration in the inversion layer. Additionally, nanostructuring and efficient surface passivation allow for a reliable device response with incident angles up to 70°. We expect the considered device to improve data quality, reduce the area of photodiodes as well as decrease the cost per pixel.

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Figure 1: Cross-section of the photodiode structure.
Figure 2: Spectral response and external quantum efficiency (EQE) of our photodiode and other state-of-the-art diodes.
Figure 3: Measured currentvoltage curves in the dark and under continuous-wave laser illumination.
Figure 4: Simulated electric field and charge-carrier concentrations as a function of depth from the device front surface.
Figure 5: Absorption spectra of b-Si textured and planar surfaces as well as the reflectance of b-Si at different incidence angles.


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The authors acknowledge Aalto University Micronova Nanofabrication Centre for providing facilities. M.A.J. was funded through the European Metrology Research Programme (EMRP) Project SIB57 NEWSTAR. P.R. was funded through EMRP project ENG53 ThinErgy. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. V.V., J.H. and D.V. were funded by the Finnish Funding Agency for Innovation TEKES through project Radi2014. The authors thank S. Juottonen for assembling sample diodes to substrates for connecting to the measurement set-ups, F. Manoocheri and A. Vaskuri for measuring the light response, V. Kübler for the angle-dependent reflectance measurements and Y. Bao for help with the electrical characterization.

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M.A.J., P.R., V.V. and H.S. conceived and designed the experiments. P.R and V.V. designed the sample manufacturing process. D.V. designed the device masks together with P.R. and V.V. and performed process simulations. J.H. performed the device simulations. P.R. and D.V. manufactured the samples. M.A.J., P.R., V.V., J.H. and H.S. analysed the data and wrote the paper.

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Correspondence to Hele Savin.

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The authors declare no competing financial interests.

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Juntunen, M., Heinonen, J., Vähänissi, V. et al. Near-unity quantum efficiency of broadband black silicon photodiodes with an induced junction. Nature Photon 10, 777–781 (2016).

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