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, such as diamond, is dominated by a high concentration of very low-energy electrons. Previous work has used the appearance of a low-energy feature in measured energy spectra to establish the presence of a negative electron affinity NEA.at the emitting surface. In this letter, secondary electron emission spectroscopy is used to study the energy distribution of secondary electrons emitted from semiconductor surfaces having different electron affinities. We conclusively show that the emitted electron distribution depends strongly on the position of the vacuum level relative to the internal electron distribution. In fact, a low-energy peak is observed in energy spectra measured at GaN, diamond, and Si surfaces having a small but positiÍe electron affinity, and the intensity and width of the peak increase steadily as the electron affinity decreases. Consequently, a low-energy structure in measured energy spectra is not sufficient evidence of a NEA. q1999 Elsevier Science B.V. All rights reserved.