29 July 2010 Gallium nitride photocathodes for imaging photon counters
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Abstract
Gallium nitride opaque and semitransparent photocathodes provide high ultraviolet quantum efficiencies from 100 nm to a long wavelength cutoff at ~380 nm. P (Mg) doped GaN photocathode layers ~100 nm thick with a barrier layer of AlN (22 nm) on sapphire substrates also have low out of band response, and are highly robust. Opaque GaN photocathodes are relatively easy to optimize, and consistently provide high quantum efficiency (70% at 120 nm) provided the surface cleaning and activation (Cs) processes are well established. We have used two dimensional photon counting imaging microchannel plate detectors, with an active area of 25 mm diameter, to investigate the imaging characteristics of semitransparent GaN photocathodes. These can be produced with high (20%) efficiency, but the thickness and conductivity of the GaN must be carefully optimized. High spatial resolution of ~50 μm with low intrinsic background (~7 events sec-1 cm-2) and good image uniformity have been achieved. Selectively patterned deposited GaN photocathodes have also been used to allow quick diagnostics of optimization parameters. GaN photocathodes of both types show great promise for future detector applications in ultraviolet Astrophysical instruments.
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Oswald H. W. Siegmund, Oswald H. W. Siegmund, Jeffrey S. Hull, Jeffrey S. Hull, Anton S. Tremsin, Anton S. Tremsin, Jason B. McPhate, Jason B. McPhate, Amir M. Dabiran, Amir M. Dabiran, } "Gallium nitride photocathodes for imaging photon counters", Proc. SPIE 7732, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, 77324T (29 July 2010); doi: 10.1117/12.857863; https://doi.org/10.1117/12.857863
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