Interpretation of low-energy feature in energy spectra measured from surfaces with low or negative electron affinity

The secondary electron distribution generated in wide bandgap material, suc h as diamond, is dominated by a high concentration of very low-energy elect rons. Previous work has used the appearance of a low-energy feature in meas ured energy spectra to establish the presence of a negative electron affini ty (NEA) at the emitting surface. In this letter, secondary electron emissi on spectroscopy is used to study the energy distribution of secondary elect rons emitted from semiconductor surfaces having different electron affiniti es. We conclusively show that the emitted electron distribution depends str ongly on the position of the vacuum level relative to the internal electron distribution. In fact, a low-energy peak is observed in energy spectra mea sured at GaN, diamond, and Si surfaces having a small but positive electron affinity. and the intensity and width of the peak increase steadily as the electron affinity decreases. Consequently, a low-energy structure in measu red energy spectra is not sufficient evidence of a NEA. (C) 1999 Elsevier S cience B.V. All rights reserved.