Chemical Tuning of Metal-Semiconductor Interfaces

We report a study of the Schottky barrier for Pb films grown on Si surfaces terminated by various metals (Ag, In, Au, and Pb) to explore the atomic-scale physics of the interface barrier and a means to control the barrier height. Electronic confinement by the Schottky barrier results in quantum well states in the Pb films, which are measured by angle-resolved photoemission. The barrier height is determined from the atomic-layer-resolved energy levels and the line widths. A calculation based on the known interface chemistry and the electronegativity yields predicted barrier heights in good agreement with the experiment.

Figure 1

(A) Photoemission intensity as a function of energy and film thickness for Pb films deposited on the Au-$6\times 6$ terminated Si(111) surface. The intensity maxima (brighter regions) correspond to quantum well states. (B) The solid curves indicated the evolution of the quantum well energies based on a simultaneous fit to the data for the four systems. The quantum number $n$ for each branch is indicated. The dashed lines indicate the branches based on the alternate quantum number $p=N-2n-1$ used previously for rough films.

Figure 2

Width of quantum well peaks as a function of energy for the four terminations studied. The vertical line in each case denotes the position of the confinement edge as the midpoint between the adjacent confined and resonant peak widths.

Figure 3

Experimental (circles) and predicted (line) Schottky barrier heights plotted against the interface Si charge parameter $Q$.