Photodiode innovation offers ozone depletion monitoring benefits

Photodiode innovation offers ozone depletion monitoring benefits

Technology News |
By eeNews Europe

Although UVC radiation does not normally reach the Earth’s surface, it can leak through to below the hole in the ozone layer. Monitoring the radiation is a way of tracking the hole in the ozone layer, and photodiodes that measure UVC are also used as flame sensors and for space communications.

Shinji Nakagomi and colleagues at Ishinomaki Senshu University in Japan have built a photodiode that can detect the whole range of UVC light while remaining insensitive to visible light from the sun.  Both features have previously eluded designers of existing devices. The photodiodes claim to be ‘solar blind’ and are more sensitive to the UVC range.

Many photodiodes are based on a p-n junction, in which a semiconductor that carries a positive charge is put in contact with the same semiconductor that instead carries negative charge (electrons). When light with sufficient energy (short wavelength) strikes atoms near the interface between the two semiconductors – called p-type and n-type, respectively – it generates mobile electrons and holes, boosting electrical current across the p-n junction and signaling the presence of light.

Other photodiodes made from materials like aluminum nitride and diamond are sensitive only to a limited range of UVC light. But recently, gallium oxide has shown promise because it is sensitive to the entire UVC range and is ‘solar blind’. The problem, however, is that it is difficult to make p-type gallium oxide.

Instead of a photodiode based on a conventional p-n junction, the researchers built one based on a heterojunction, which is a p-n junction that incorporates two different semiconductors. The team used gallium oxide and silicon carbide, and found that their device responds quickly to UV light – within milliseconds – and has little dark current, which is the intrinsic electrical current that flows through the device even in the absence of light. Minimal dark current is important for a sensitive photodiode.

"The most important aspect about our device is that it is based on a heterojunction between gallium oxide and silicon carbide," said Nakagomi. "This gallium oxide and silicon carbide photodiode is promising for the detection of UV light."

The paper entitled ‘Deep ultraviolet photodiodes based on B-Ga2O3/SiC Heterojunction’ is authored by Shinji Nakagomi, Toshihiro Momo, Syuhei Takahashi, and Yoshihiro Kokubun and appears in the journal Applied Physics Letters.

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