Euro-Indo collaboration develops new photo-detector
Photo-detectors that analyse scattered light in the ultraviolet (UV) range of the spectrum are often used in situations where the rapid detection of hazardous biological and chemical agents in air is required. Each type of material demonstrates a sort of optical fingerprint; this can be shown, for example, by laser excitation. To this end, photo-detectors with an extremely narrow bandwidth are required, which only respond to particular wavelengths. Enter European and Indian scientists, who teamed up to offer the world an innovative solution. Their work was published in the journal Applied Physics Letters in February 2007.
Photo-detectors analyse scattered light in the ultraviolet (UV) range.
An international consortium of scientists, which includes the Paul Drude Institute for Solid State Electronics (PDI) in Berlin, Germany and colleagues from Spain and India, has developed such a detector for UV radiation. This particular detector has a bandwidth of only six nanometres (nm). This means its bandwidth is five times narrower than that of a comparable photo-detector. The device is also sensitive to polarised light, which helps to reduce the scattered background radiation.
Prof. Dr Holger T. Grahn from the PDI headed the team of researchers, who developed the detector using a photo-sensitive layer of non-polar gallium nitride (GaN) on a substrate of lithium aluminate (LiAlO2). The active GaN layer is 0.4 micrometres thick. To give you some idea of the size, it is 10 times smaller than the diameter of the average dust particle.
The GaN layer was produced at the Paul Drude Institute by Oliver Brandt, while the photo-detector was produced at the Universidad Polotécnica de Madrid in Madrid, Spain by Carlos Rivera, Jose Luis Pau and Eliaz Munoz. The necessary measurements were carried out at the Tata Institute of Fundamental Research in Mumbai, India by Sandip Ghosh.
The new device is suitable for the identification of airborne chemical and biological agents in real time. These agents are excited by a laser beam in order to produce fluorescence in the UV range of the spectrum. The detector is then used to extract the optical fingerprint from the scattered light. A large number of photo-detectors, with very narrow bandwidths, is necessary so as to simultaneously detect as many different substances as possible. This requires each device being sensitive to a particular wavelength. The photo-detector developed by the international consortium is merely the size of a pin head and detects UV radiation of only 360 nm.