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

Scanning tunneling spectroscopy without shifts related to band bending was utilized to study tip-induced gap states in lightly doped Si(100) (rho = 12 -25 Omega 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 ban d gap was also observed as the tip approached the sample, suggesting the ev olution of a continuum of tip-induced gap states. These results can be expl ained in terms of an emission dominant-tunnel model where the tunneling cur rent is controlled by electron emission from traps in the band gap. The exp eriments described herein demonstrate that scanning tunneling microscopy ca n be used as a powerful tool for probing the origin and evolution of the su rface states. (C) 1999 American Institute of Physics. [S0003-6951(99)00908- 0].