Quantitative modeling of secondary electron emission from slow-ion bombardment on semiconductors

Abstract

When slow ions incident on a surface are neutralized, the excess potential energy is passed on to an electron inside the surface, leading to emission of secondary electrons. The microscopic description of this process, as well as the calculation of the secondary electron yield, is a challenging problem due to its complexity as well as its sensitivity to surface properties. One of the first quantitative descriptions was articulated in the 1950s by Hagstrum, who based his calculation on a parametrization of the density of states of the material. In this paper, we present a model for calculating the secondary electron yield, derived from Hagstrum's initial approach. We use first-principles density functional theory calculations to acquire the necessary input and introduce the concept of electron cascades to Hagstrum's model in order to improve the calculated spectra, as well as remove its reliance on fitting parameters. We apply our model to He + and Ne + ions incident on Ge(111) and Si(111) and obtain yield spectra that match closely to the experimental results of Hagstrum.

Negative ion formation by neutral hydrogen atom grazing scattering from a LiF(100) surface

“…and Z ¼ 3.5 a.u. cases, which is in reasonable agreement with the conclusion that electron transfer mainly occurs near the trajectory turning point (within the Z˛ [2,5] a.u. range) of the projectile trajectory.…”

“…In eqn (2), 20,28,37 which is created by the dipolar potential eld produced by the formed negative ion and the hole on the surface in the nal state of the electron capture reaction. U image (Z,v) is the image interaction between the formed H À and the image charge which produced by the eld polarization of the H À gas to the LiF crystal in the nal state of the electron capture reaction.…”

“…4(b) displays the electron capture probability P cap as a function of projectile velocity v for xed surface altitudes of Z ¼ 3,3.5,4 a.u. Considering the generally effective electron capture surface altitude range of Z˛ [2,5] a.u. 30,44 for a neutral atom under grazing scattering from an insulator surface with keV projectile energy, the Z averaged probability of hP cap (Z,v)i Z˛ [2,5] a.u.…”

“…The electron capture probability increases with projectile velocity v and decreases with surface altitude Z. The averaged probability hP cap (-Z,v)i Z˛ [2,5] a.u. is located between the electron capture probabilities of theZ ¼ 3.0 a.u.…”

“…Charged particle-surface interactions as an important eld have been intensively researched over several decades. Most studies have focused on, for instance, ion-or electron-induced sputtering and desorption, 1 ion stimulated surface electron emission, [2][3][4] energy loss, 5 and ion induced surface nanostructures. [6][7][8][9] The charge state in scattered beams aer projectile scattering from an insulator ionic-crystal surface has received much attention.…”