Results from Cs activated GaN photocathode development for MCP detector systems at NASA GSFC

Norton, Timothy; Woodgate, B. E.; Stock, J.; Hilton, G. C.; Ulmer, M. P.; Aslam, Shahid; Vispute, R. D.

doi:10.1117/12.507528

Cited by 24 publications

(10 citation statements)

References 3 publications

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“…b Stabilized QE is obtained after the cesiated GaN has had a chance to stabilize. c Previously reported 4 . d Also previously reported, except a subsequent processing of the sample.…”

Section: Set Up and Proceduresmentioning

confidence: 95%

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

Stock¹,

Hilton

Woodgate

et al. 2005

SPIE Proceedings

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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.

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“…b Stabilized QE is obtained after the cesiated GaN has had a chance to stabilize. c Previously reported 4 . d Also previously reported, except a subsequent processing of the sample.…”

Section: Set Up and Proceduresmentioning

confidence: 95%

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

Stock¹,

Hilton

Woodgate

et al. 2005

SPIE Proceedings

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“…The GaN photocathode prepared by Machuca et al 5 had a quantum efficiency (QE) of 50% at 310 nm after Cs activation. Norton et al 6 achieved a high‐quality GaN emission layer with 40% QE at 185 nm by using Cs treatment. Du et al 7 discussed the adsorption mechanism of Cs based on first principles and showed that Cs adsorption can reduce work function which is consistent with the experimental results.…”

Section: Introductionmentioning

confidence: 99%

Structural and electronic properties of Cs‐adsorbed GaN monolayer and bilayer based on first principles

Liu

2021

Int J Energy Res

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A negative electron affinity photocathode can be obtained by adsorbing Cs on the emission layer surface of photocathode, which greatly improves the number of electrons escaped and the quantum efficiency. Based on first principles, this paper studies the structural and electronic properties of Cs-adsorbed GaN monolayer and bilayer. The results reveal that the Cs-adsorbed GaN monolayer is the most stable when Cs atom is adsorbed at T Ga site. There is a significant charge transfer between Cs atom and GaN monolayer, and the difference in electronegativity makes electrons of Cs atom transfer to GaN monolayer system. Cs adsorption can reduce band gap, work function, and electron affinity, which is conducive to the escape of electrons and improvement of quantum efficiency. Cs adsorption is helpful for tuning optical properties of GaN monolayer. For the GaN bilayer, greater stability and lower work function make the Cs adsorbed above the top layer of GaN bilayer be more beneficial to the improvement of photoelectric performance. Novelty StatementBased on first principles, this paper studies the structure and electric properties of Cs-adsorbed GaN monolayer and bilayer. Cs adsorption can reduce band gap, work function, and electron affinity, which is conducive to the escape of electrons and improvement of quantum efficiency. And for the GaN bilayer, greater stability and lower work function make the Cs adsorbed above the top layer of GaN bilayer be more beneficial to the improvement of photoelectric performance. K E Y W O R D Scharge transfer, Cs adsorption, first principles, GaN bilayer, GaN monolayer | INTRODUCTIONCs-activated GaN photocathode has been applied in flame detection, 1 corona detection, 2 ultraviolet communication, 3 and other fields. Because Cs activation plays an important role in reducing surface barrier and work function, it helps the photocathode achieve a negative electron affinity state which is beneficial to photoelectron emission. 4 In recent years, there are many theoretical and experimental studies on Cs-absorbed GaN surface reported successively. The GaN photocathode prepared by Machuca et al. 5 had a quantum efficiency (QE) of 50% at 310 nm after Cs activation. Norton et al 6 achieved a high-quality GaN emission layer with 40% QE at 185 nm by using Cs treatment. Du et al 7 discussed the adsorption mechanism of Cs based on first principles and showed that Cs adsorption can reduce

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“…For example, Norton et al used an ultrahigh vacuum system to cesiumize GaN and achieved a quantum efficiency greater than 40% at 185 nm. [ 3 ] Ulmer et al obtained the NEA state through a typical Cs or Cs, O activation process on p‐type GaN, the GaN photocathode in the reflection mode achieved a quantum efficiency of up to 56% at a wavelength of 200 nm, and that of the GaN photocathode in transmission mode is 30%. [ 4 ] Shahedipour et al and Uchiyama et al used Mg‐doped p‐type GaN materials to prepare a reflective NEA GaN photocathode with a quantum efficiency of more than 30%.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of Electron Collection and Light Trapping of Inclined GaN and AlGaN Nanowire Arrays

Liu

Zhangyang

2021

Energy Tech

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The structural design of excellent absorption and electron collection is the main challenge of the nanowire array (NWA) photocathode. Herein, the light trapping and photoemission performance of GaN and graded compositional AlGaN‐inclined NWA are systematically researched. The finite‐difference time domain method (FDTD) is used to calculate the light absorption under different inclined angles and array spacings. The results show that the NWA with an inclined angle of 0.4°–0.6° has greater light‐trapping capacity, which obtains up to 97% light absorption at a wavelength of 267 nm. The inclined graded compositional AlGaN NWA with a built‐in electric field has better photoemission performance. The external electric field further improves the electron collection capacity of the NWA cathode. The inclined AlGaN NWA cathode with the best parameters θ = 0.6°, L = 180 nm, and Eout = 2 V μm−1 obtains a quantum efficiency of 47.57% and collection efficiency of 31.09%. The study of the inclined graded compositional AlGaN NWA cathode assisted by the electric field provides an effective method for further utilization of incident light and emitted electrons.

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Results from Cs activated GaN photocathode development for MCP detector systems at NASA GSFC

Cited by 24 publications

References 3 publications

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

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

Structural and electronic properties of Cs‐adsorbed GaN monolayer and bilayer based on first principles

Enhancement of Electron Collection and Light Trapping of Inclined GaN and AlGaN Nanowire Arrays

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