detectors technology
Extreme ultraviolet imaging with hybrid AlGaN arrays
Silicon extreme ultraviolet detector arrays require non-standard methods to be prevented from receiving longer wavelength radiation, e.g. by using multiple filters. Switching to AlGaN equivalents increases robustness and eliminates the need to block out visible and infrared light, which in turn boosts detector performance, say IMEC’s Pawel Malinowski, Kyriaki Minoglou and Piet De Moor.
A
t first glance, the fields of solar astronomy and silicon chip manufacture are poles apart. But they do have one thing in common – the need for efficient and reliable imaging of extreme ultraviolet (EUV) radiation, which spans the range 10-120 nm.
In solar physics, there is tremendous interest in phenomena occurring on the Sun’s surface (photosphere) and in its atmosphere (chromosphere and corona), such as coronal mass ejections and flares that cause staggering amounts of radiation to be emitted towards the Earth. Such processes occur at extremely high energies, so very short wavelength detectors are needed to observe what is taking place.
Meanwhile, the silicon industry is continuing its never- ending goal of shrinking transistor sizes by starting to develop lithographic processes involving EUV patterning. This requires detectors sensitive at these wavelengths, which can aid efforts to find and refine techniques for controlling the properties of the UV beam. Solar scientists and silicon engineers can use existing silicon devices for
the EUV detection needs. But greater performance is possible by turning to detectors based on GaN, which have an inherently simpler system design and are more robust to UV radiation.
Silicon’s weaknesses One of the biggest advantages of using silicon to build any device is that this material and its related process technology are mature, and consequently well understood. However, its bandgap of 1.12 eV means that it absorbs not only ultraviolet radiation, but the entire visible spectrum too, plus infrared radiation up to around 1100nm (see Figure 1). This makes silicon the perfect material for the most common digital cameras and advanced imagers operating in the visible part of the spectrum. But if silicon is employed as the active material for detecting ultraviolet radiation, its sensitivity to the longer wavelengths must be taken into account.
Image Courtesy of
In solar science this is important considering the fact that the solar spectrum is several orders of magnitude more intense in the EUV than in the visible range. In practice,
NASA/SDO and the AIA, EVE, and
HMI science teams. January / February 2011
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