Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003spie.5164..134s&link_type=abstract
UV/EUV and Visible Space Instrumentation for Astronomy II. Edited by Siegmund, Oswald H. W. Proceedings of the SPIE, Volume 516
Astronomy and Astrophysics
Astronomy
3
Scientific paper
The nitride-III semiconductors, in particular GaN (band gap energy 3.5 eV), AlN (band gap 6.2 eV) and their alloys AlxGa1-xN are attractive as UV photo-convertors with applications as photocathodes for position sensitive detector systems. These can "fill the gap" in the 150-400nm wavelength regime between alkali halide photocathodes (<2000Å), and the various optical photocathodes (>4000Å, mutlialkali & GaAs). Currently CsTe photocathodes have fairly low efficiency (Fig. 1) in the 100nm to 300nm regime are sensitive to contamination and have no tolerance to gas exposure. We have prepared and measured a number of GaN photocathodes in opaque and semitransparent modes, achieving >50% quantum efficiency in opaque mode and ~35% in semitransparent mode (Fig. 2). The GaN photocathodes are stable over periods of >1 year and are robust enough to be re-activated many times. The cutoff wavelength is sharp, with a rapid decline in quantum efficiency at ~380-400nm. Application of GaN photocathodes in imaging devices should be feasible in the near future. Further performance improvements are also expected as GaN fabrication and processing techniques are refined.
Malloy James
Martin Adrian
Siegmund Oswald H. W.
Tremsin Anton S.
Ulmer Melville P.
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