Use of Auger Electron Spectroscopy in Determining the Effect of Carbon and Other Surface Contaminants on GaAs–Cs–O Photocathodes

Abstract

Auger electron spectroscopy has been used to measure quantitatively the amount of carbon contamination on GaAs–Cs–O photosurfaces. It appears that approximately one monolayer of carbon is sufficient to reduce the photoyield to zero.

Auger Electron Spectroscopy Study of GaAs Substrate Cleaning Procedures

“…Two samples were placed in the beam path to enhance the Si-N absorption. The very broad absorption region around 800 to 900 cm -1 is attributed to Si-N bonding (1,3,4,7). The feature around 1110 cm -1 is due to oxygen in bulk silicon ~.12), whereas silicon dioxide has an absorption band at 1060 cm -1…”

“…In addition, unwanted and uncontrolled residues left on the surface after cleaning can diffuse into the epitaxial layer during growth. Substrate cleaning procedures are generally developed empirically, only a few studies (1)(2)(3)(4) attempting to measure the actual composition of the substrate surface having appeared in the literature. Auger electron spectroscopy (AES) is a sensitive surface analytical probe and can provide semiquantitative measurement of residues left on the substrate surface after cleaning.…”

GaAs photocathode cleaning by atomic hydrogen from a plasma source

“…GaAs is used extensively to fabricate negative-electronaffinity (NEA) photocathodes [1][2][3][4][5][6][7][8][9][10][11]. To reduce the number of electrons emitted by purely thermal excitation, heavy p-doping, bringing the Fermi level close to the valence band, is used.…”

“…Chemical cleaning followed by heating in ultra-high vacuum (UHV) has been used as the standard procedure for cleaning the surfaces prior to NEA activation [2,8]. For GaAs, typical contaminants observed on the surface are chlorine, sulphur, oxygen and carbon [9]. Heat cleaning can remove chlorine, sulphur and oxygen, but the carbon is not removed and it dominates the problem of surface cleaning [7].…”

“…In the presence of carbon, an interfacial barrier of GaAs-C-Cs 2 O is formed that does not allow the low-energy electrons to escape into the vacuum. It has been shown that one monolayer of carbon is sufficient to reduce the photoemission to zero [9]. Chemical cleaning is a time-consuming process and does not provide a carbon-free surface.…”