Elimination of spectral shifts associated with tip-induced band bending in scanning tunneling spectroscopy of lightly doped silicon

It has been demonstrated in this letter that spectral shifts arising from the tip-induced band bending on the lightly doped silicon can be eliminated by forming an accumulation layer in p-type silicon or an inversion layer in n-type silicon by using a Pt–Ir tip. Illumination is also required for n-type silicon in order to eliminate shifts associated with deep depletion caused by tunneling leakage currents. Using the approaches described herein, energy gaps of approximately 1.1 eV are determined for both p-type and n-type silicon. Furthermore, identical bias polarity is observed in current–voltage curves for both n-type and p-type silicon, and can be explained by the direction of the band bending induced by Pt–Ir on lightly doped samples. These results suggest that scanning tunneling spectroscopy can be used to reveal various features associated with surface states and bulk properties in lightly doped samples by using high work function metals such as Pt–Ir in place of lower work function metals such as W.