A team from Aalto University in Espoo, Finland, has created a black silicon photodetector that has exceeded 100%—the first to surpass what was thought to be the theoretical limit for external quantum efficiency.
The newly developed photovoltaic material has supposedly attained 130% efficiency. "When we saw the results, we could hardly believe our eyes. Straight away, we wanted to verify the results by independent measurements," said Professor Hele Savin, Electron Physics research group head, in the press release from Aalto University.
They requested independent measurements from another institute—the German National Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB). The German metrology institute, headquartered in Brunswick, boasts the most accurate measurement capabilities in the European continent.
"After seeing the results, I instantly realized that this is a significant breakthrough—and at the same time, a much-welcomed step forward for us metrologists dreaming of higher sensitivities," said Dr. Lutz Werner, Head of the Laboratory of Detector Radiometry at the PTB.
The study is already submitted to the American Physical Society (APS Physics).
An External Quantum Efficiency Breakthrough
Ultraviolet sensors have a wide variety of applications, from metrology to biotechnology to industrial environments. The research team has noted that the efficiency of currently available UV sensors is relatively low.
The external quantum efficiency is set at 100%, theoretically achieved when a single photon enters a system and generates one electron in output. With the Aalto University black silicon photodetector breaking the so-called "one proton - one electron barrier," they have posted a 130% efficiency—for every single incoming proton, the material generates about 1.3 electrons in output.
In the study, it was identified that the unusually high external quantum efficiency was brought about by the charge-carrier multiplication that occurs inside silicon nanostructures. Furthermore, this process is triggered by high-energy particles, like protons. Researchers have not yet observed this charge-carrier multiplication property due to electrical and optical losses. These factors leave the material's external quantum efficiency to less than 100%.
"We can collect all multiplicated charge carriers without a need for separate external biasing as our nanostructured device is free of recombination and reflection losses," Savin added.
Applications of a Super-Efficient UV Photodetector
"Our detectors are gaining a lot of attraction at the moment, especially in biotechnology and industrial process monitoring," said Dr. Mikko Juntunen, CEO of Elfys Inc.—a company specializing in photodetectors and light detection applications founded by Aalto University researchers.
A recent study led by Chinese researchers has demonstrated the possibility of a UV photodetector, promising applications in both military and civilian uses. Their solar-blind photodetector, which does not detect infrared, visible, and near-UV light but senses UV lights, can operate within a narrow range with high responsivity. However, its posted external quantum efficiency is at 32%, and it is already above conventional values.
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One of the most important applications of UV photodetectors is in spectroscopy, the study of how matter responds to electromagnetic radiation. Photodetectors, such as the black silicon developed by Aalto University, are responsible for taking the light (optical energy) and converting it into an electrical current, which then gives the readout needed by the equipment. A light sensor with increased efficiency could theoretically provide more precise readings, eliminating the need to compensate for different kinds of losses.
