Cs Br ∕ Ga N heterojunction photoelectron source

Abstract

Formation of cesium peroxide and cesium superoxide on InP photocathode activated by cesium and oxygenNegative electron affinity group III-nitride photocathode demonstrated as a high performance electron source Experimental results on a new CsBr/ GaN heterojunction photocathode structure are presented. The results indicate a fourfold improvement in photoyield relative to CsBr/ Cr photocathodes. A model is presented based on intraband states in CsBr and electron injection from the GaN ͑with 1% addition of indium͒ substrate to explain the observed photoyield enhancement. The photocathode lifetime at high current density ͑Ͼ40 A / cm 2 ͒ is limited by laser heating of the small illuminated area. Calculations are presented for sapphire and diamond substrates, indicating a factor of 20 reduction in temperature for the latter. The results are encouraging for the realization of a high photoyield photocathode operating at high current density with long lifetime.

RobustCsBr/Cuphotocathodes for the linac coherent light source

“…This initial behavior is expected from the creation of color centers in the material and the transfer of Cs to the surface as described in Refs. [3][4][5][6], and differs from the UV surface cleaning shown in Fig. 1 samples was measured before coating.…”

“…In the case of CsBr=GaN photocathodes, due to the better alignment of the conduction bands of CsBr and GaN substrate, the direct electron injections from the GaN substrate through the CsBr film are enhanced. Thus CsBr=GaN cathodes offer a large enhancement in the quantum efficiency relative to CsBr=Cr photocathodes [5,6].…”

“…of many hundreds of hours when illuminated with 257 nm (4.8 eV) radiation either in the transmission or reflection modes [4]. Operation below the band gap of CsBr ( 7:3 eV) was attributed [3][4][5][6] to (i) intraband states present in the CsBr layer with an energy about 3.7 eV below the conduction band, and (ii) the direct electron injection from the metal to CsBr layer. Electrons occupying those intraband states can perform transitions to the continuum with an incident photon energy of only 4.8 eV.…”

Evaluation of electron energy spread in CsBr based photocathodes

“…The GaN photocathode structure 5 consists of a 100 nm thick GaN layer, p-type 1 ϫ 10 18 cm −3 ͑Mg doped͒ and an AlN buffer layer 500 Å thick molecular beam epitaxy grown on a c-axis double side polished sapphire substrate ͑0.5 mm thick͒. The GaN photocathode structure 5 consists of a 100 nm thick GaN layer, p-type 1 ϫ 10 18 cm −3 ͑Mg doped͒ and an AlN buffer layer 500 Å thick molecular beam epitaxy grown on a c-axis double side polished sapphire substrate ͑0.5 mm thick͒.…”

Analysis of surface electromagnetic wave resonant structures for potential application in an array of compact photoelectron sources

“…Robust CsBr photoemitters have been demonstrated and characterized, and they show significant promise for multiple electron-beam systems. [2][3][4][5] The virtual source size of an electron source is determined by the size of the emission area. Therefore, the laser spot, which controls the size of the photoemission area, determines the virtual source size.…”