THE AG/N-INSB(110) INTERFACE AT 10-K - 1ST OBSERVATION OF AN ANOMALOUS FERMI-LEVEL PINNING

The Fermi-level (E(F)) position at the Ag/n-InSb(110) interface has been studied via angle-resolved UV photoelectron spectroscopy (ARUPS) of the In and Sb 4d core levels and the valence band using synchrotron radiation. Ag films in the thickness range between 0.001 and 10 monolayers were deposited onto cleaved InSb(110) surfaces at T almost-equal-to 10 and T almost-equal-to 300 K. At 10 K layer-by-layer and at 300 K cluster growth occurs. The following phenomena, related to the E(F) position at the Ag/n-InSb(110) interface, are reported for the first time: (1) deposition of 0.06 +/- 0.02 monolayers of Ag at 10 K shifts E(F) 350 meV into the conduction band, thus forming a two-dimensional electronic channel at the interface (downward band bending); (2) heating to 300 K (after 10 K deposition) moves E(F) down to the level typical for 300 K deposition; (3) for Ag deposits of more than 0.1 monolayer, E(F) moves down to the conduction band minimum by further deposition at 10 K; (4) for 300 K deposition E(F) is almost independent of Ag coverage. We conclude that pinning of E(F) takes place through surface states of different types: (1) donor-type states introduced under adsorption of individual Ag atoms at 10 K, and (2) metal-induced states introduced through metallization of the Ag deposit.