Study on photoemission mechanism for negative electron affinity GaN vacuum electron source

Abstract

The whole process including photoelectron excitation, transportation from bulk to surface and escape to vacuum by traversing surface barrier was analyzed in detail. Photoelectron excitation relates to the band structure of photocathode material and the absorption coefficient of the material. In the bulk of GaN photocathode, the photoelectrons mainly are transited into Γ valley first, when the energy is great enough, the photoelectrons can scatter into higher M‐L valley or A valley from Γ valley. The electrons excitated in conduction band will move from bulk to surface by diffusing or drifting. The diffuse length for GaN photocathode is about 3μm by calculating. After the thermal electrons of Γ valley move into surface band bend area, they will drift to the surface because of the electric field of band bend area. The transmission coefficient relates to the incident electron energy, the height and width of the surface potential. The quantum yield formulas of NEA GaN photocathode were gotten by solving the diffuse equation of non‐equilibrium carriers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detection of Aqueous Solvated Electrons Produced by Photoemission from Solids Using Transient Absorption Measurements

“…In vacuum, this combination of properties is referred to as negative electron affinity (NEA). − An important property of NEA materials is that the efficiency of electron emission increases greatly compared with materials having positive electron affinity. While many materials exhibiting NEA are known, ,, the vast majority are highly reactive with water, making them unsuitable for intentional creation of solvated electrons by photoelectrochemical processes.…”