need help on microfabrication electronics hw

4. You have 3 metals available to form a contact with an n-type silicon wafer. These metals are Al, Au, and Cu, whose work functions are 4.28 ev, 5.1 ev, and 4.65 eV, respectively. Which metal would you choose to form the smallest Schottky barrier? The susceptibility (x ) of silicon is 4.05 eV. Assume that Schottky's theory correctly predicts the behavior of all of these contacts