ElFys Oy

Black silicon photodiodes


Schematic of Black silicon photodiode.

ElFys Oy offers induced junction black silicon photodiodes with external quantum efficiency (EQE) greater than 96% over a broad range of wavelengths (250 to 950 nm). The collection efficiency has been enhanced by employing a surface nanostructuring technique combined with a conformal ALD alumina coating. This results into reliable and nearly ideal device response with incident angles up to 70 degrees. The induced junction virtually eliminates  Auger recombination of light generated charge carriers and this way prevents the formation of a dead layer. Additionally, the applied highly effective surface passivation technology, eliminates surface recombination. This combination significantly boosts the collection efficiency of signal charges generated really close to the photodiode top surface, yielding an exceptional over 100% quantum efficiency for ultraviolet light. Furthermore, a nearly ideal response is maintained over the entire optical spectrum shown in figures (see also reference [1]). Integrating this technology into silicon imaging detectors leads to significant performance improvements in terms of sensitivity and spectral range particularly in ultraviolet region [2].

Corresponding response curve and comparison to typical pn-junction and UV-enhanced silicon photodiodes. Ideal response corresponding to 100% EQE is also shown for reference.


[1] M. A. Juntunen, J. Heinonen, V. Vähänissi, P. Repo, D. Valluru, and H. Savin, “Near-unity quan-tum efficiency of broadband black silicon photodiodes with an induced junction”. Nature Photonics, 10(12), 777-781, 2016

[2] M. A. Juntunen, J. Heinonen, H. S. Laine, V. Vähänissi, P. Repo, A. Vaskuri and H. Savin, ”N-type Induced junction Black Silicon photodiode for UV detection”. Proc. SPIE 10249, Integrated Pho-tonics: Materials, Devices, and Applications IV, 102490I, 2017


A silicon wafer and black silicon photodiodes.

Individual photodiodes are available with active areas e.g. 2,4 x 2,4 mm2, Ø 5mm (19,6 mm2) and 5 x 5 mm2. We can also manufacture custom design sizes and shapes as well as arrays and matrices of photodiodes, which enable a drop in replacement of your current photodiode

  • Maximum chip size about 50 x 70 mm2
  • Minimum individual active area size about 0,1*0,1mm2
  • Typical parameters of black silicon photodiodes are listed in Table I

The high EQE results from zero reflection of black silicon surface combined with no dead layer of induced junction. These innovations improve the absorption of light and collection of generated charge carriers. In the ultraviolet light region this means 2-3 times higher response compared to other silicon photodiodes optimized for UV detection. Similarly, the black silicon photodiodes give around 30% more signal in scintillator applications compared to standard photodiodes as the broad and high EQE improves overall response to emission spectrum of typical scintillator materials.

Table I Typical leakage current, response and capacitance values of the Black Silicon photodiodes.

Lekage current pA/mm2 Response A/W Capacitance (pF/mm2)
at 10 mV at -5 V at -100 V at 250 nm at 400 nm at 910 nm at 0 V at -1 V
8 35 50 0.23 0.30 0.70 2.81 1.15



ElFys Oy was founded in fall 2017 to commercialize the black silicon photodiode technology invented by a group of university researchers. The company owns the intellectual property rights to the technologies of both planar and black silicon n-type induced junction photodiodes. The company utilizies the state-of-the-art processing facilities of Micronova Nanofabrication Center, which are suitable for both flexible R&D and semi-mass production. One main aspect of the technology is the sub-micron structures of black silicon that result into longer optical path and close to zero reflection within wide ranges of wavelengths and acceptance angles. When combined with ALD deposited aluminium oxide layer, an induced junction is formed which results into nearly ideal photodetector [1].  Integrating this technology into silicon imaging detectors leads significant performance improvements in terms of sensitivity and spectral range particularly in ultraviolet region [2].

Partners of the company also have vast expertise on silicon photovoltaics and related research. The structure and operation principles of solar cells and photodiodes are very similar and thus innovations from solar cells can often be applied to photodiodes and vice versa. Topics like surface passivation and defect engineering are integral parts of the manufacturing process and essential for achieving the superior response of our photodiodes.


ElFys, Inc. is participating in the ESA Business Incubation Centre Finland.

22.11.2018 ElFys has joined the ESA Business Incubation Centre Finland.

In the ESA BIC Finland, ElFys aims to develop its involvement in space applications and pursue a deep market penetration of the high-performance radiation detection for both space and terrestrial applications.


Photo: Mikko Raskinen, Aalto University.

30.8.2018 CEO Mikko Juntunen introduced Black Silicon Photodiode technology to the President of France

During his official state visit to Finland, the French President Emmanuel Macron visited Startup Sauna of Aalto University in Otaniemi Campus to see the Finnish innovation system in action. He was hosted by the prime minister of Finland Juha Sipilä. ElFys Chief Executive Officer Dr. Mikko A. Juntunen was invited to the event by the French Embassy in Helsinki due to ElFys participating in the YEi program of France (see the news of June 11). Mikko introduced the Black Silicon Photodiode technology to the President, gave feedback of the YEi program, and discussed about ElFys interests regarding French partnering and market potential.  The program is cofinanced by French Institute in Finland, French embassy in Finland, Business Finland and Business France.


12.7.2018 European Space Agency contracted a technology development project from ElFys

ElFys Oy is proud to announce that we have signed a contract with European Space Agency (ESA) for technology development project “Application of Black Silicon Surface Treatment to Photodiodes and Silicon Drift Detectors”. The goal of the project is to evaluate the benefits of the superior sensitivity achieved with black silicon and induced junction in space applications. In addition to optical characterization, we will also investigate our detectors’ response to X-rays. We are extremely excited to see if our technology can revolutionize also the X-ray spectroscopy measurements. Another equally exciting part of the ESA project will be an extensive environmental and radiation stress campaign. These tests will reveal how well our detectors can tolerate the extreme conditions of space.

11.6.2018 ElFys has been selected to participate the YEi program in France

ElFys has been selected to participate the YEi program in Young Enterprise initiative Start in France program organized by the French ministry of Europe and foreign affairs and Scientific Offices in French Embassies. 30 companies have been selected globally to this program and ElFys is proud to be one of them. The program is cofinanced by French Institute in Finland, French embassy in Finland, Business Finland and Business France

28.4.2018 ElFys in startup column in Tekniikka&Talous

The articles shortly presents ElFys and the several business opportunities related to ElFys’s exceptional sensitive black silicon photodiode.

4.3.2018 Hele Savin’s interview in Kauppalehti Optio

Hele Savin is one of the co-founders of ElFys. This article describes the basic research and the achieved results using black silicon in the silicon solar cells. Read the article here (only in Finnish).


D.Sc. (Tech) Mikko A. Juntunen, CEO

email: firstname.lastname(at)elfys.fi
phone +358 40 860 9663


Mikko Juntunen serves as Chief Executive Officer of ElFys Oy. He is a key inventor of the Black Silicon Photodiode technology which combined his background knowledge and experience of radiation and photodetectors to the world class understanding of semiconductor physics and photovoltaics of Aalto University Electron Physics Group where he worked as a senior scientist between 2013 and 2017. Juntunen has vast experience in developing, industrializing and selling science-based innovations, including starting new companies and development units. He is a physicist by education, M.Sc. in 1994 and D.Sc. in 2013 and has spent years developing detectors, first to scientific instrumentation in CERN and later to medical imaging and various other applications in Detection Technology, Inc. Juntunen holds several detector technology related patents, latest one related to Black Silicon Photodiodes. He also has industrial experience in consumer electronics manufacturing including semiconductor packaging with Nokia Mobile Phones.

D.Sc. (Tech) Antti Haarahiltunen, CTO

email: firstname.lastname(at)elfys.fi
phone +358 40 739 6048

Antti Haarahiltunen has worked at ElFys Oy as a Chief Technical Officer from 2/2018 and is one of the co-founders. Antti received his Lic. Med. degree from University of Helsinki Finland in 2018, and his M.Sc. (Tech.) and D.Sc. (Tech.) degrees in electrical engineering from the Helsinki University of Technology (TKK), Finland, in 2002 and 2007, respectively. Antti worked 2000-2016 at the Department of Micro and Nanosciences, Aalto University (formerly TKK), Finland. He was the senior scientist in several research projects  and has developed strong background in silicon material characterization, device processing and physical modeling in field of IC, PV and MEMS.  Antti is an author of over 40 journal articles, and has delivered presentations on his work throughout the world.

M.Sc. (Tech) Juha Heinonen, Project Manager

email: firstname.lastname(at)elfys.fi
phone +358 41 545 2606


Juha Heinonen has been a project manager at ElFys Oy since the beginning of 2018 and is in charge of setting up the photodiode production. He has vast expertise on the entire black silicon photodiode fabrication process including layout and process design as well as characterization of the finalized devices. Juha completed his Master’s degree in Micro and Nanosciences at Aalto University, Finland in 2016 and currently continues to pursue Ph.D. at the same university, as a side project. Topic of his and Ph.D. thesis is also related to black silicon photodiodes and thus it nicely complements his work at ElFys Oy.

D.Sc. (Tech) Chiara Modanese, Project Engineer

email: firstname.lastname(at)elfys.fi
phone +358 40 191 1886

Chiara Modanese joined ElFys Oy as a Project Engineer in the summer of 2018. She received her Ph.D. in Materials Science and Engineering from the Norwegian University of Science and Technology (NTNU), Norway in 2012, and she has then been a researcher both at NTNU (2012-2015) and at Aalto University Department of Electronics and Nanoengineering (2016-2018). She has experience in applied research along the value chain of silicon photovoltaics, from ingot crystallization to prefabricates processing in the cleanroom and characterization.


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Contact Info

+358 40 860 963
Tekniikantie 12
FI-02150 Espoo