Browsing by Author "Juntunen, Mikko A."

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  • Black silicon n-Type photodiodes with high response over wide spectral range
    (2017) Heinonen, Juha; Juntunen, Mikko A.; Laine, Hannu S.; Vähänissi, Ville; Repo, Päivikki; Dönsberg, Timo; Savin, Hele
     A4 Artikkeli konferenssijulkaisussa
    Commercial photodiodes suffer from reflection losses and different recombination losses that reduce the collection efficiency of photogenerated charge carriers. Recently, we realized a near-ideal silicon photodiode, which steps closer to the physical performance limits of silicon photodiodes than any other silicon photodiode realized before. Our device exhibits an external quantum efficiency above 95% over the wavelength range of 235-980 nm, and provides a very high response at incident angles of up to 70 degrees. The high quantum efficiency is reached by 1) virtually eliminating front surface reflectance by forming a "black silicon" nanostructured surface having dimensions in the range of wavelength of optical light and 2) using an induced junction for signal collection, formed by negatively charged alumina, instead of a conventional doped p-n junction. Here, we describe the latest efforts in further development of the photodiode technology. In particular, we report improvements both in the short wavelength response via better control of the surface quality, and superior response to photons with energies close to the silicon bandgap.
  • Effect of anode sheet resistance on rise time of black silicon induced junction photodiodes
    (2022-03-04) Heinonen, Juha; Haarahiltunen, Antti; Vähänissi, Ville; Pasanen, Toni P.; Savin, Hele; Juntunen, Mikko A.
     A4 Artikkeli konferenssijulkaisussa
    Black silicon induced junction photodiodes have been shown to have nearly ideal responsivity across a wide range of wavelengths. Another important characteristic of a high-quality photodiode is rise time which can be used to approximate bandwidth of the photodiode. We show experimentally that the rise time of black silicon photodiodes is shorter than in planar photodiodes when alumina layer with similar charge is used to make an induced junction in both. Additionally, we show that the rise time can be rather well approximated using an analytical equation, which combines Elmore delay from equivalent circuit with standard RC-delay arising from series and load resistances.
  • Industrial Applicability of Antireflection-Coating-Free Black Silicon on PERC Solar Cells and Modules
    (2018) Pasanen, Toni; Vähänissi, Ville; Wolny, Franziska; Oehlke, Alexander; Wagner, Matthias; Juntunen, Mikko A.; Heikkinen, Ismo T. S.; Salmi, Emma; Sneck, Sami; Vahlman, Henri; Tolvanen, Antti; Hyvärinen, Jaakko; Savin, Hele
     A4 Artikkeli konferenssijulkaisussa
    Black silicon (b-Si) is of particular interest within the photovoltaic community due to its ability to texture diamond wire-sawn multicrystalline silicon wafers. In this work, we apply a deep dry-etched black silicon nanotexture, which possesses less than 1 % solar-weighted reflectance with no antireflection coating (ARC), to industrial Passivated Emitter and Rear Cells (PERC). Additionally, the cells are processed further into small solar modules, which are characterized by their electrical and optical performance. The fragile nanostructures remain intact during industrial cell and module fabrication, maintaining the excellent optical properties until the final product. We show that b-Si modules with a typical cover glass retain their performance until incident angles larger than 60°, whereas the heavily increased reflectance of acidic-textured modules decreases their efficiency already after a 30° tilt. Furthermore, at an incidence angle of 70°, the efficiency of b-Si modules has reduced only 7 %, while that of the acidic-textured equivalents has decreased more than 25 %. Hence, the excellent optical properties of ARC-free b-Si are maintained also at module level. The results demonstrate that deep dry-etched b-Si nanostructures are fully applicable to current industrial PERC production facilities.
  • N-Type induced junction black silicon photodiode for UV detection
    (2017) Juntunen, Mikko A.; Heinonen, Juha; Laine, Hannu S.; Vähänissi, Ville; Repo, Päivikki; Vaskuri, Anna; Savin, Hele
     A4 Artikkeli konferenssijulkaisussa
    Commercial photodiodes suffer from reflection losses and different recombination losses that reduce the collection efficiency. Recently, we realized a near-ideal silicon photodiode that exhibits an external quantum efficiency above 95% over the wavelength range of 235-980 nm, exceeds 100% below 300nm, and provides a very high response at incident angles of up to 70 degrees. The high quantum efficiency is reached by 1) virtually eliminating front surface reflectance by forming a "black silicon" nanostructured surface having dimensions proportional to the wavelength of light to be detected and 2) using an induced junction for signal collection instead of a conventional doped p-n junction, virtually eliminating Auger recombination at the light entry surface. This recombination prevention is especially important in ultraviolet detection since ultraviolet photons are absorbed very close to device surface, where conventional photodiodes have high doping concentration causing loss of signal, but induced junction diode is able to collect virtually all charge carriers generated. In this paper, we analyse the performance of our photodiodes under ultraviolet radiation.
  • Spatial uniformity of black silicon induced junction photodiode responsivity
    (2023-03-14) Heinonen, Juha; Haarahiltunen, Antti; Vähänissi, Ville; Pasanen, Toni P.; Savin, Hele; Toivanen, Juha; Juntunen, Mikko A.
     A4 Artikkeli konferenssijulkaisussa
    Black silicon induced junction photodiodes have nearly ideal responsivity across a wide range of wavelengths between 175-1100 nm, with external quantum efficiency over 99 % at visible wavelengths, when a single spot is measured using light beam between 1 to 2mm in diameter. The spatial uniformity of responsivity is also an important characteristic of a high-quality photodiode, when considering its usage as a reference in photometry. We study here the spatial uniformity of responsivity of large area (8mmx8mm) black silicon photodiodes at 405 nm wavelength. Our results show that the spatial non-uniformity is less than 0.5 % over 90 % of the surface area, and thus the photodiodes meet the thigh criteria typically set for reference standards and are hence suitable for such application.
  • Temperature dependency of responsivity and dark current of nearly ideal black silicon photodiodes
    (2021-03-05) Heinonen, Juha; Haarahiltunen, Antti; Serue, Michael; Kriukova, Daria; Vähänissi, Ville; Pasanen, Toni P.; Savin, Hele; Juntunen, Mikko A.
     A4 Artikkeli konferenssijulkaisussa
    A high-quality photodiode has high signal-to-noise ratio (SNR), which is ultimately defined by the responsivity and dark current of the photodiode. Black silicon induced junction photodiodes have been shown to have nearly ideal responsivity across a wide range of wavelengths between 175-1100 nm at room temperature (RT). Here we present their spectral responsivity stability and dark current at different temperatures. Both quantities show temperature dependencies similar to conventional pn-junction photodiodes, proving that black silicon photodiodes maintain their improved SNR also at temperatures other than RT.