The doping-density dependence of scanning tunneling spectroscopy on lightly doped hydrogen-terminated Si(100) (resistivities in the range of 0.2–12 Ω cm) was investigated in air with and without illumination. The observed doping-density dependence is consistent with a generation model in which the changes in the three-dimensional depletion region, induced by a scanning tunneling microscopy tip, contributes to changes in the concentration of thermally and/or photogenerated carriers in lightly doped samples. These results suggest that scanning tunneling spectroscopy can be used to image variations in dopant density in lightly doped samples.

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.

In this article, a tunneling-generation-avalanche model has been proposed to explain the reverse bias current–voltage behavior observed at a tip/air/p-type silicon junction. Based on this model, under conditions where the applied bias is more negative than the flat band voltage, the current will be dominated by generation processes, which has significant doping density dependence. Since mechanically cut tips, used in this work, can have complicated geometries, geometric effects, such as extended gates and concentration of the electrical field must be taken into account. By taking these factors into account, good agreement between theory and experiments can be achieved. Finally, in the presence of illumination, p/p+ junctions can be delineated successfully by taking advantage of the generation process. These results demonstrate that scanning tunneling microscopy can be used as a powerful tool for characterizing semiconductor devices.

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.

The properties of the Sn-doped AlxGa1−xAs alloys with various compositions have been studied by deep level transient spectroscopy and photocapacitance methods. Two deep donor levels with the thermal activation energies of 0.19 and 0.32 eV are found in all of the samples. Detailed data for the thermal emission and capture activation energies, optical ionization energies, and their composition dependence are given for the first time. Because their electronic properties are similar to that of the typical Si DX level in AlxGa1−xAs, it is concluded that both Sn-related levels are the DX-like levels.