Researchers at the Indian Institute of Science have designed a new high speed device that can detect ultraviolet (UV) light more efficiently. The device is also cheaper than the existing UV photodetectors.
A photodetector is a sensor that can sense light. We come across photodetectors in numerous places like in a simple TV remote, automatic opening of doors in malls to cameras. They are also used in light based communication, and for detecting energy from outer space.
The fabricated device can have several applications like in chemical and biological analysis for example: ozone, pollutants, and most organic compounds characterization etc., in flame detection (fire alarms, missile warning etc.), in optical communications (inter-satellite communications), for emitter calibration (instrumentation, UV lithography), for Astronomical studies and radiation detection etc.
"In our case, the UV photodetector is simple, less expensive, has high photodetection speed with visible blind UV illumination sensitive only (highly selective)", said Abha Misra, Assistant Professor, Department of Instrumentation and Applied Physics, Indian Institute of Science, who led the work along with research scholar Buddha Boruah.
Speed, detection sensitivity and cost are the important parameters for such detectors. "In silicon based photodetectors, it is very difficult to perform only visible blind UV photo detection due to its intermediate optical band gap. Other detectors are commercially expensive and difficult to miniaturize", said Misra. They devised a smart way of addressing these issues.
The material Zinc Oxide (ZnO) is a semiconductor, similar to the silicon used in solar cells. It is highly preferable in ultraviolet photodetection due to its unique optical properties. However, ZnO has a high resistivity – it opposes the flow of current – and hence is slow in the detection of UV illumination.
The proposed device has ZnO in the form of 'quantum dots' – miniaturized tiny particles which have a large surface area. ZnO is integrated with graphene, a 2D material known for its excellent electronic properties. When the device is illuminated with UV light, a large photocurrent is generated, as graphene and ZnO form a special type of contact such that current can flow only in one direction. Electrons are known to travel at a very high speed in Graphene. Thus the device response is very rapid. Also, due to the energy difference between ZnO and Graphene, there is very little current leakage when there is no UV illumination. This implies better detection efficiency and thus device performance.
About the authors:
Abha Misra is an Assistant Professor with the Department of Instrumentation and Applied Physics (IAP), Indian Institute of Science. http://iap.iisc.ernet.in/~abha/
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