The neutralization of 3 keV Li${}^{+}$ ions scattered from Si(111) is measured as a function of doping density, dopant type, and hydrogen coverage. When the surfaces are saturated with hydrogen to unpin the Fermi level, the neutral fractions decrease for lightly doped samples but become anomalously large for highly doped $n$-type Si. A simple model that includes the many-body band-gap narrowing effect predicts the neutralization to good accuracy using a tunneling mechanism similar to the free-electron gas jellium model normally employed for ion/metal interactions, but excluding levels in the gap.

• Received 10 September 2011

DOI:https://doi.org/10.1103/PhysRevB.85.165307