Current missile warning systems operating in the ultraviolet (UV) part of the spectrum are quite cost-intensive and require large installation space. The systems are based on image intensifier systems and complex filter structures, since missile detection in solar-blind UV (UV-C, < 280 nm) can only be achieved with the very high gain of an intensifier tube with MCPs (micro channel plates).
Semiconductor detectors made of materials such as silicon (Si), silicon carbide (SiC) or gallium phosphide (GaP) do not achieve the necessary specifications in terms of sensitivity and dark current to be considered as an alternative solution. In addition, these materials are not solar-blind, so the complex filter structures would still be needed.
Detectors based on AlGaN could be a possible alternative in the future. Due to the relatively large band gap, AlGaN is intrinsically blind to visible and infrared light ("visible blind"). Variations in the composition also make it possible to design the semiconductor material "solar-blind". Furthermore, AlGaN detectors are characterized by their radiation resistance even at high optical powers. The solarization that often occurs with external filters can be avoided thanks to the integrated filter structure.
AlGaN-based detectors were developed in a cooperation of several Fraunhofer Institutes with different applications in mind: Water treatment, exhaust gas analysis, UV curing of paints and adhesives, remote sensing, and detection of missiles.
A scanning line scan camera based on AlGaN line sensors was developed at Fraunhofer IOSB. The spectral sensitivity of the camera can be selected by changing the sensor used. Currently UV-A, UV-B and UV-C detectors are available. The graph below (right) gives an impression of the spectral properties of these detectors. The developed line scan camera is shown on the left. The last image shows the view from the laboratory window in three spectral ranges and illustrates the advantage of solar-blind detectors.
In case you are in need of a sensor solution for this interesting spectral range, please contact us. We will be happy to advise you and work with you to find possible solutions.