Semiconductor surfaces with negative electron affinity

Abstract

The review of the studies of GaAs and GaN surfaces performed by the authors at the Institute of Semiconductor Physics (Novosibirsk) are presented. The results of these studies are used for further elucidation of the physics of photoemission from the surfaces with negative electron affinity (NEA) and improving the performance of NEA-photocathodes. In particular, the requirements to III-V semiconductor surfaces, which are necessary for the preparation of NEA photocathodes with ultimate parameters, are analyzed. To meet these requirements, the experimental procedures aimed at preparing atomically clean and flat surfaces with certain reconstructions, which are subsequently activated to the state of NEA in ultra-high vacuum by coadsorption of cesium and oxygen, are developed. The surface morphological, structural, and electronic phenomena occurring on various stages of these preparation procedures are studied, and the relation of these phenomena to the physical limits of NEA-photocathode performance are discussed.

Photoelectron Transportation Dynamics in GaAs Photocathodes

“…In other words, solving a gradient-doped device in general can be converted into solving a uniform-doping problem for n e f f (x,t) and then multiplying the result with exp − A 2 x + 1 2 v d t . This global exponential term can be viewed effectively as a descending exponential envelope propagating at a speed of 1 2 v d toward the device surface (i.e., the -x direction). It is the embodiment of the so-called drift-assisted carrier transportation 24 , which accelerates the accumulation of photoelectrons on the device surface.…”

“…Negative-electron-affinity (NEA) III-V semiconductor photocathodes have been widely used in night vision, ultraviolet detection, polarized-electron generation, and photonenhancement in emission tubes [1][2][3] . Compared to the traditional metal-or alkali-based photocathodes, III-V photocathodes are able to achieve higher quantum efficiencies (QE) 4,5 .…”