Progress on development of UV photocathodes for photon-counting applications at NASA GSFC

Abstract

The development of high quantum efficiency photoemissive detectors is recognized as a significant advancement for astronomical missions requiring photon-counting detection. For solar-blind NUV detection, current missions (GALEX, STIS) using Cs 2 Te detectors are limited to ~10 % DQE. Emphasis in recent years has been to develop high QE (>50%) GaN and AlGaN photocathodes (among a few others) that can then be integrated into imaging detectors suitable for future UV missions.We report on progress we have made in developing GaN photocathodes and discuss our observations related to parameters that affect efficiency and stability, including intrinsic material properties, surface preparation, and the vacuum environment. We have achieved a QE in one case of 65% at 185 nm and are evaluating the stability of these high QEs. We also discuss plans for incorporating GaN photocathodes into imaging and non-imaging sealed devices in order to demonstrate long term stability.

MCP detector development for UV space missions

“…It is expected that the first cesium layer is strongly bound on GaN, but even at room temperature other cesium layers sublimate slowly if the cesium partial vapor pressure within the volume to which the photocathode is exposed is too low. This is an expected behavior as we have measured it ourselves and as reported by Stock et al (2005) 17 . Again, our measurements shortly before and after sealing show that at the given temperature and duration of the sealing process in our UHV system there is no major change in the response of the photocathode.…”

Study on photoemission mechanism for negative electron affinity GaN vacuum electron source

“…Negative electron affinity (NEA) gallium nitride (GaN) photocathode has many good performance characteristics, such as high quantum efficiency, low dark current and concentrated electron energy distribution and so on [1][2][3]. As a proper candidate for vacuum electron source material, NEA GaN photocathode is made up of by sapphire (substrate), AIN (buffer layer) and activated layer (covered Cs or Cs/O).…”

Reactivation of gallium nitride photocathode with cesium in a high vacuum system

“…With the robust characteristics as rapid spectral response, high quantum efficiency and stable physical and chemical properties, GaN photocathode can be widely used in ultraviolet detection, photon-counting and vacuum electron source area [1][2][3][4][5][6][7]. Recently, comparatively high quantum efficiencies of GaN photocathode have been achieved, including more than 70% QE for reflection mode and about 35% QE for transmission mode by some groups [1,2].…”