Photoelectron Emission from Si–Gd–O Cathode

Electronic and emission properties of photocathodes fabricated on the basis of multilayered structures of oxidized Gd atoms deposited on the Si(100) surface and additionally covered with fresh layers of Gd atoms have been studied as functions of the structure holding time under vacuum, by using the methods of photoelectron (h nu = 1.9 divided by 10.2 eV) and Auger electron spectroscopies. It is found that, although the photocathode work function is equal to about 0.5 eV at some research stages, the photoemission is registered only at h nu >= 2.8 eV. The analysis of the results allowed us to propose a model for the energy structure of the photocathode that agrees with experimental data. According to this model, the near-surface region of a photocathode, about 1 nm in thickness, consists of Gd2O3 with the energy gap width of about 5.3 eV. The distance from the Fermi level to the conduction band bottom equals about 2.7 eV in the Gd2O3 bulk. In the forbidden gap below the Fermi level, the bulk states and filled surface states associated with structural defects. A complicated dipole layer appears on the surface, and this gives the substantial reduction of the work function.