CCD backside coatings optimized for 200-300 nm observations

The high QE and large variety of formats makes modern back illuminated Charge-coupled devices (CCDs) nearly ideal detectors for most scientific imaging applications. In the ultraviolet (UV), however, quantum efficiency (QE) instability with temperature and with environmental conditions has limited their widespread use, especially for space applications. We have developed several techniques to achieve stable and high QE in the 200-300 nm wavelength range with back illuminated CCDs fabricated by various manufacturers. In this paper we report peak QE of over 90% at 240 nm (uncorrected from quantum yield). We describe a series of tests which demonstrate stability of these devices with temperature, humidity, and UV illumination. These results are all based in the chemisorption backside coating processes developed at the Steward Observatory CCD Laboratory.