Scanning tunneling microscopy and spectroscopy for studying cross-sectioned Si(100)

Abstract

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are used to investigate a cross-sectional surface of Si(100) prepared by an ex situ cleave HF-dip technique. The agreement between the measured current–voltage spectra (I/Vs) and those calculated with an unpinned surface for both n- and p-type bulk surfaces is good, thus indicating that the prepared surface is unpinned and the model is valid. Both the experimental and calculated I/Vs show three components of current: tunneling out of valence-band states (VB), tunneling through dopant states (D), and tunneling into conduction-band states (CB). As demonstrated by experiment, in agreement with the model, the shape of the I/Vs allows the discrimination of n-type from p-type surfaces. Furthermore, the model indicates that by measuring the dopant state current D-component STM/STS is sensitive to the carrier density within the range of 1018–1021 cm−3. This suggests that this ex situ cleave sample preparation can be used to produce unpinned cross-sectional surfaces for ultra-shallow dopant profiles in Si(100). On such a surface STM/STS can be used to determine the carrier profile that results from the dopant profile.