Observation of tip-induced gap states in lightly doped Si(100) using scanning tunneling spectroscopy

Abstract

Scanning tunneling spectroscopy without shifts related to band bending was utilized to study tip-induced gap states in lightly doped Si(100) (ρ=12–25 Ω cm). The separation dependence of scanning tunneling spectroscopy revealed a reversible interaction between the tip and sample. A “U” shape curve of normalized differential conductivity versus sample bias in the band gap was also observed as the tip approached the sample, suggesting the evolution of a continuum of tip-induced gap states. These results can be explained in terms of an emission dominant-tunnel model where the tunneling current is controlled by electron emission from traps in the band gap. The experiments described herein demonstrate that scanning tunneling microscopy can be used as a powerful tool for probing the origin and evolution of the surface states.