A Model for Emission Yield from Planar Photocathodes Based on Photon-Enhanced Thermionic Emission or Negative-Electron-Affinity Photoemission

A general model is presented for electron emission yield from planar photocathodes that accounts for arbitrary cathode thickness and finite recombination velocities at both front and back surfaces. This treatment is applicable to negative electron affinity emitters as well as positive electron affinity cathodes, which have been predicted to be useful for energy conversion. The emission model is based on a simple one-dimensional steady-state diffusion treatment. The resulting relation for electron yield is used to model emission from thinfilm cathodes with material parameters similar to GaAs. Cathode thickness and recombination at the emissive surface are found to strongly affect emission yield from cathodes, yet the magnitude of the effect greatly depends upon the emission mechanism. A predictable optimal film thickness is found from a balance between optical absorption, surface recombination, and emission rate. Disciplines Mechanical Engineering Comments Sahasrabuddhe, K., Schwede, J., Bargatin, I., Jean, J., Howe, R., Shen, Z., & Melosh, N. (2012). A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negativeelectron-affinity photoemission. Journal of Applied Physics, 112(9), 094907. doi: 10.1063/1.4764106 Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. Author(s) Kunal Sahasrabuddhe, Jared W. Schwede, Igor Bargatin, Joel Jean, Roger T. Howe, Zhi-Xun Shen, and Nicholas A. Melosh This journal article is available at ScholarlyCommons: http://repository.upenn.edu/meam_papers/297 A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negative-electron-affinity photoemission Kunal Sahasrabuddhe, Jared W. Schwede, Igor Bargatin, Joel Jean, Roger T. Howe, Zhi-Xun Shen, and Nicholas A. Melosh Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA Department of Physics and Applied Physics, Stanford University, Stanford, California 94305, USA Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA Department of Mechanical Engineering and Applied Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA (Received 7 August 2012; accepted 9 October 2012; published online 6 November 2012) A general model is presented for electron emission yield from planar photocathodes that accounts for arbitrary cathode thickness and finite recombination velocities at both front and back surfaces. This treatment is applicable to negative electron affinity emitters as well as positive electron affinity cathodes, which have been predicted to be useful for energy conversion. The emission model is based on a simple one-dimensional steady-state diffusion treatment. The resulting relation for electron yield is used to model emission from thin-film cathodes with material parameters similar to GaAs. Cathode thickness and recombination at the emissive surface are found to strongly affect emission yield from cathodes, yet the magnitude of the effect greatly depends upon the emission mechanism. A predictable optimal film thickness is found from a balance between optical absorption, surface recombination, and emission rate. VC 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764106]