Origin of Schottky Barriers in Gold Contacts on $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}(110)$

Gold contacts on $n$-type $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}(110)$ have been investigated using scanning tunneling microscopy and spectroscopy in cross-sectional configuration. In spatially resolved current voltage spectroscopy the Schottky barrier potential is visible. We find signatures of delocalized gap states at the interface decaying into the semiconductor and observe a defect density at the interface below $3\times {10}^{13}\mathrm{c}{\mathrm{m}}^{-2}$. Both findings support that the Fermi level pinning at the $\mathrm{A}\mathrm{u}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}(110)$ interface is dominated by metal-induced gap states.

Figure 1

(a) Cross-sectional measurement geometry and coordinate system. (b) $40\mathrm{n}\mathrm{m}$ by $40\mathrm{n}\mathrm{m}$ constant current topography of the $\mathrm{A}\mathrm{u}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}(110)$ interface taken at $U=-2.0\mathrm{V}$ and $I=200\mathrm{p}\mathrm{A}$. Gray scale range $110\mathrm{p}\mathrm{m}$. The letters $A$ to $F$ mark the areas over which the spectra of Fig. 2 were averaged.

Figure 2

Spatially resolved tunneling spectroscopy measurements of the $\mathrm{A}\mathrm{u}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}(110)$ contact. The spectra are taken and averaged in the stripe regions $A$ to $F$ indicated in Fig. 1b. The curves $B$ to $F$ are vertically shifted for clarity.

Figure 3

Images of $\mathrm{l}\mathrm{o}\mathrm{g}(dI/dU)$, averaged over different energy ranges near the band gap. Gray scale ${10}^{-13}$ to ${10}^{-10.5}\mathrm{A}/\mathrm{V}$. (a) $U=-0.6$ to $-0.8\mathrm{V}$. (b) $U=-0.8$ to $-1.0\mathrm{V}$. The region of the Au film is shaded black for better visibility.

Figure 4

Spatial decay of the differential conductivity $dI/dU$ perpendicular to the interface. (a) Sections through maps of $dI/dU$ for different bias voltages. (b) Decay length of the $dI/dU$ sections against voltage.