Thermal emittance measurements for electron beams produced from bulk and superlattice negative electron affinity photocathodes

Abstract

Extremely low emittance electron beams are required for next generation accelerators. GaAs semiconductor photocathodes with negative electron affinity ͑NEA͒ surfaces have an intrinsic advantage for generating such low emittance beams and the thermal emittance as low as 0.1 mm mrad is expected in ideal case. The thermal emittance of photoelectrons was measured for two different NEA photocathodes: a bulk-GaAs photocathode and a GaAs-GaAsP superlattice strained photocathode. The normalized root-mean-sqare emittances for the beam radius of 1.0 mm were as low as 0.20− 0.29± 0.02 and 0.15± 0.02 mm mrad, respectively. A comparison of these results shows that the superlattice photocathode minimizes the thermal emittance for photon excitation energies higher than the band gap energy.

Highly spin-polarized electron photocathode based on GaAs–GaAsP superlattice grown on mosaic-structured buffer layer

“…Spin-polarized electrons were characterized by the NPES-3 [15] and the JPES-1 [13]. These systems were designed and fabricated in Nagoya University and consist of a gun and a Mott polarization analyzer.…”

Phonon-mediated desorption of image-bound electrons from dielectric surfaces

“…Interesting in this respect are also electronegative dielectric structures used in electron emitting devices such as cesium-doped silicon oxide films [22][23][24] and GaAs-based heterostructures. [25][26][27] In contrast to intrinsic surface states, 28 originating either from the abrupt disappearance of the periodic lattice potential or unsaturated bonds at the surface, image states are not localized at the edge but typically a few Å in front of the solid. An external electron approaching the solid from the vacuum with a kinetic energy below the lowest unoccupied intrinsic electron state of the surface may thus get trapped ͑adsorbed͒ in these states provided it can get rid of its excess energy.…”

Negative electron affinity GaAs wire-array photocathodes

“…Recently, with the rapid development of space detection, high-resolution night-vision imaging, next-generation electron accelerators, lowenergy electron microscopes, and electron beam lithography, an ever-pressing demand has arisen for photocathodes with higher sensitivity, wider spectral response range, higher emission current density, and higher spin polarization. Thus, some new GaAs-based photoemission material structures, such as graded doping/band-gap [6][7][8], strained [9], and superlattice structures [10][11][12], have been proposed to increase the quantum efficiency or spin polarization of GaAs-based photocathodes. However, all of these new photoemission materials rely on GaAs-based epitaxial thin films as the active layers of photocathodes.…”