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M. Baylac, JLab baylac@jlab

Atomic hydrogen exposure of strained layer GaAs photocathodes. M. Baylac, JLab baylac@jlab.org. P. Adderley, J. Brittian, J. Clark, A. Day, J. Grames, J. Hansknecht, M. Poelker, P. Rutt, C. Sinclair, M. Stutzman. . N. GaAs. e. QE =. N. . -. -. +. +. -. N - N. N + N. e. e.

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M. Baylac, JLab baylac@jlab

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  1. Atomic hydrogen exposure of strained layer GaAs photocathodes M. Baylac, JLab baylac@jlab.org P. Adderley, J. Brittian, J. Clark, A. Day, J. Grames, J. Hansknecht, M. Poelker, P. Rutt, C. Sinclair, M. Stutzman

  2. N GaAs e QE = N  - - + + - N - N N + N e e e P = Quantum Efficiency: ~ 0.3% e e e ~ 75% Polarization: Polarized electrons • Nuclear physics program requires an electron source with High efficiency & High polarization • Photoemission out of strained layer GaAs semiconductors -100 kV

  3. ~ G Atomic hydrogen source wafer ~300C • Semiconductor samples cleaned by exposure to atomic hydrogen • H2 dissociation via RF inductive discharge • Voltage can be applied on wafer to enhance/reduce effect of ions 15 cm 100 MHz 20 W Mc.Alpine & Schildknecht, Proceeding of IRE, 1959 (2099) H2, or D2

  4. P (dose) – P (bare) ~ -10% at bandgap e e Polarization vs Hydrogen dose • Significant depolarization • Wavelength dependent • Effect seen with and w/o ions

  5. Why this depolarization? • Related to strain? Tested and ruled out • Hydrogen trapped in material? Increased anneal cycle (12 h instead of 2): no effect • Variation of angle of incidence of light onto wafer? Roughness measurements with high resolution profilometry (Andy Wu @ Jlab ): Bare surface: RMS ~ 155 A Hydrogen exposed: RMS ~ 8500 A

  6. Conclusions • Atomic hydrogen exposure necessary to obtain high QE with anodized samples • Heavy dose depolarizes semiconductor significantly • Depolarization with/without H ions, unexplained enhancement • Excessive dose can reduce QE • Surface analysis shows roughened surface which can explain depolarization (underway) • Need prepare clean sample with minimal hydrogen exposure

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