Detector tiny detects airborne pollutants

New device measures and analyzes UV radiation

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Scientists have developed a new, pin-head-sized detector that can quickly and accurately detect toxins and other threatening substances in the air.


A laser excites molecules to glow and the high-precision photodetector measures and analyzes the backscattered light in the ultraviolet (UV) range. Each substance has a kind of optical fingerprint on which it can be safely determined.

Tiny active layer

Extremely narrow-band photodetectors, which are only sensitive to specific wavelengths, are necessary for this work. The new component, presented by scientists from the Paul Drude Institute for Solid State Electronics (PDI) together with colleagues from India and Spain in the journal Applied Physics Letters, has a detection bandwidth of only six nanometers and is thus five times narrower than comparable photodetectors. In addition, the detector can detect the polarization of the light. This helps to filter out disturbing background radiation.

The international team of scientists led by Holger Grahn (PDI) developed the detector using a photosensitive layer of non-polar gallium nitride (GaN) on a substrate of lithium aluminate (LiAlO2). The active GaN layer is only 0.4 microns thick - about one tenth of the diameter of a speck of dust. display

The GaN layer was produced at the PDI. Scientists led by Carlos Rivera, Jose Luis Pau and Elias Muñoz structured the photodetector at Madrid's Universidad Politécnica de Madrid and measurements were taken by Sandip Ghosh at the Tata Institute of Fundamental Research in Mumbai, India.

Many photosensitive elements

The new detector is suitable for the real-time detection of biological and chemical substances in the air. In order to be able to detect as many substances as possible at once, many small photosensitive elements are required, each of which reacts exactly to very specific, different wavelengths, ie have a narrow spectral bandwidth.

The element that the international team now unveiled is about the size of a pinhead and detects only ultraviolet radiation with a wavelength of 360 nanometers.

(idw - Forschungsverbund Berlin, 06.06.2007 - DLO)