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At present ultraviolet sensors are utilized in numerous fields ranging from various spectroscopy applications via biotechnical innovations to industrial process control. Despite of this, the performance of current UV sensors is surprisingly poor. Here, we break the theoretical Shockley-Queisser limit and demonstrate a device with a certified external quantum efficiency (EQE) above 130% in UV range without external amplification. The record high performance is obtained using a nanostructured silicon photodiode with self-induced junction. We show that the high efficiency is based on effective utilization of multiple carrier generation by impact ionization taking place in the nanostructures. While the results can readily have a significant impact on the UV-sensor industry, the underlying technological concept can be applied to other semiconductor materials, thereby extending above unity response to longer wavelengths.

Ikonen, E. (2017). Predictable quantum efficient detector based on n-type silicon photodiodes. Metrologia, 54(6) AbstractThe predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO 2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al 2 O 3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatiallyOriginal content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.

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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.