Modeling electron emission and surface effects from diamond cathodes

We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surf...

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Bibliographic Details
Published in:Journal of applied physics 2015-02, Vol.117 (5)
Main Authors: Dimitrov, D. A., Smithe, D., Cary, J. R., Ben-Zvi, I., Rao, T., Smedley, J., Wang, E.
Format: Article
Language:English
Subjects:
APPROXIMATIONS
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
DIAMONDS
EFFECTIVE MASS
ELECTRIC FIELDS
ELECTRON EMISSION
ELECTRONIC STRUCTURE
ELECTRONS
HYDROGENATION
PHOTOCATHODES
SEMICONDUCTOR MATERIALS
SURFACE POTENTIAL
SURFACES
THREE-DIMENSIONAL LATTICES
V CODES
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Summary:We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass, and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. Using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.
ISSN:0021-8979
1089-7550