PAC2013 - List of Authors (Dimitrov, D.A.)

Paper	Title	Page
MOPBA21	Modeling Localized States and Band Bending Effects on Electron Emission Ion from GaAs	225
	D.A. Dimitrov, Y. Choi, C. Nieter Tech-X, Boulder, Colorado, USA I.V. Bazarov, S.S. Karkare, W.J. Schaff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I. Ben-Zvi, T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA
	Funding: The authors wish to acknowledge the U.S. Department of Energy (DOE) and the National Science Foundation for funding under grants DOE DE-SC0006246, NSF DMR-0807731, and DOE DE-SC0003965. High acceptor doping of GaAs and (Cs, O) or (Cs, F) surface coating leads to downward band bending terminating with effective negative electron affinity surface. The periodicity breaking at the surface together with the formed potential leads to one or more localized states in the band bending region together with effective Fermi level pinning. We report results on how to calculate the band bending potential, the Fermi level pinning, and localized states as functions of GaAs p-doping density, surface density of states, and temperature. We also consider how these surface properties affect electron emission.

TUPMA15	Monte Carlo Simulations of Charge Transport and Electron Emission from GaAs Photocathodes	616
	Y. Choi, D.A. Dimitrov, C. Nieter Tech-X, Boulder, Colorado, USA I.V. Bazarov, S.S. Karkare Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under SBIR grant DE-SC0006246 and Early Career DE-SC0003965. The need for a bright electron beam is increasing in the fields of x-ray science, electron diffraction and electron microscopy which are required for colliders. GaAs-based photocathodes have the potential to produce high-brightness, unpolarized and polarized, electron beams with performance that meets modern collider requirements. Even after decades of investigation, however, the exact mechanism of electron emission from GaAs is not well understood. Therefore, we investigate photoemission from a GaAs photocathode using detailed Monte Carlo electron transport simulations. Instead of a simple stepwise potential, we consider a triangular barrier including the effect of the image charge to take into account the effect of the applied field on the emission probability. The simulation results are compared with the experimental results for quantum eﬃciency, angular and energy distributions of emitted electrons without the assumption of any ad hoc parameters.

TUPSM30	Modeling the Development and Mitigation of Charge Accumulation for Photo Emission Electron Guns	700
	C. Nieter, Y. Choi, D.A. Dimitrov Tech-X, Boulder, Colorado, USA
	Funding: Project supported by DOE SBIR grant DE-SC0006246 One potential problem with the operation of photo emission electron guns is the potential for charge to accumulate on the emission surface depending on how the biasing voltage is applied to the gun. If the voltage is applied away from the emission surface there is the potential for charge to accumulate on the emission surface since not all electrons will necessarily be emitted. This charge accumulation may affect the gun operation by reducing the accelerating field in the gun. We report on simulations that demonstrate this potential issue as well as simulations that test a potential solution where a secondary voltage is applied periodically to clear the accumulated charge.

Paper

Title

Page

Modeling Localized States and Band Bending Effects on Electron Emission Ion from GaAs

225

D.A. Dimitrov, Y. Choi, C. Nieter
Tech-X, Boulder, Colorado, USA
I.V. Bazarov, S.S. Karkare, W.J. Schaff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I. Ben-Zvi, T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA

Funding: The authors wish to acknowledge the U.S. Department of Energy (DOE) and the National Science Foundation for funding under grants DOE DE-SC0006246, NSF DMR-0807731, and DOE DE-SC0003965.
High acceptor doping of GaAs and (Cs, O) or (Cs, F) surface coating leads to downward band bending terminating with effective negative electron affinity surface. The periodicity breaking at the surface together with the formed potential leads to one or more localized states in the band bending region together with effective Fermi level pinning. We report results on how to calculate the band bending potential, the Fermi level pinning, and localized states as functions of GaAs p-doping density, surface density of states, and temperature. We also consider how these surface properties affect electron emission.

TUPMA15

Monte Carlo Simulations of Charge Transport and Electron Emission from GaAs Photocathodes

616

Y. Choi, D.A. Dimitrov, C. Nieter
Tech-X, Boulder, Colorado, USA
I.V. Bazarov, S.S. Karkare
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under SBIR grant DE-SC0006246 and Early Career DE-SC0003965.
The need for a bright electron beam is increasing in the fields of x-ray science, electron diffraction and electron microscopy which are required for colliders. GaAs-based photocathodes have the potential to produce high-brightness, unpolarized and polarized, electron beams with performance that meets modern collider requirements. Even after decades of investigation, however, the exact mechanism of electron emission from GaAs is not well understood. Therefore, we investigate photoemission from a GaAs photocathode using detailed Monte Carlo electron transport simulations. Instead of a simple stepwise potential, we consider a triangular barrier including the effect of the image charge to take into account the effect of the applied field on the emission probability. The simulation results are compared with the experimental results for quantum eﬃciency, angular and energy distributions of emitted electrons without the assumption of any ad hoc parameters.

TUPSM30

Modeling the Development and Mitigation of Charge Accumulation for Photo Emission Electron Guns

700

C. Nieter, Y. Choi, D.A. Dimitrov
Tech-X, Boulder, Colorado, USA

Funding: Project supported by DOE SBIR grant DE-SC0006246
One potential problem with the operation of photo emission electron guns is the potential for charge to accumulate on the emission surface depending on how the biasing voltage is applied to the gun. If the voltage is applied away from the emission surface there is the potential for charge to accumulate on the emission surface since not all electrons will necessarily be emitted. This charge accumulation may affect the gun operation by reducing the accelerating field in the gun. We report on simulations that demonstrate this potential issue as well as simulations that test a potential solution where a secondary voltage is applied periodically to clear the accumulated charge.