Effect of interface band structure on hot-electron attenuation lengths in Au thin films

The hot-electron attenuation length in thin Au films has been determined by means of ballistic electron emission microscopy on $\mathrm{Au}∕\mathrm{Si}\left(111\right)$, $\mathrm{Au}∕\mathrm{Si}\left(001\right)$, and $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$ Schottky diodes. The attenuation length measured for $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$ was approximately ten times shorter than attenuation lengths measured on the Si substrates. In addition, the slope of the attenuation length vs tip bias decreases above the $X$ conduction band minimum in GaAs. These observations are attributed to differences in the amount of allowed parallel momentum at the interfaces of both semiconductors. These results suggest that these apparent attenuation lengths are not an intrinsic property of the metal and can be utilized as a powerful method to probe the band structure at metal-semiconductor interfaces.

Figure 1

Typical BEEM spectra obtained from a $19\mathrm{nm}$ thick $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$ Schottky diode with a tunneling current of $5.0\mathrm{nA}$. The three threshold voltages were found to occur at $V_1=0.76$, $V_2=1.03$, and $V_3=1.18\pm 0.04\mathrm{eV}$. The inset shows the derivative of the BEEM spectra.

Figure 2

(200) x-ray pole figures for $26\mathrm{nm}$ thick Au: (a) $\mathrm{Au}∕\mathrm{Si}\left(111\right)$, (b) $\mathrm{Au}∕\mathrm{Si}\left(001\right)$, (c) GaAs(001) (substrate only), and (d) $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$.

Figure 3

Normalized BEEM current as a function of Au thickness for a tip bias of $1.2\mathrm{eV}$ obtained using $\mathrm{Au}∕\mathrm{Si}\left(111\right)$, $\mathrm{Au}∕\mathrm{Si}\left(001\right)$, and $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$ samples. The solid lines represent the fits to Eq. (1).

Figure 4

(a) Energetic dependence of the attenuation length measured using $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$, $\mathrm{Au}∕\mathrm{Si}\left(001\right)$, and $\mathrm{Au}∕\mathrm{Si}\left(111\right)$ Schottky diodes. (b) Enlarged plot of the attenuation lengths measured on the $\mathrm{Au}∕\mathrm{Ga}\mathrm{As}\left(001\right)$ samples.