CONTROL OF SCHOTTKY AND OHMIC INTERFACES BY UNPINNING FERMI-LEVEL

We propose the first systematical method to control Schottky barrier h eights of metal/semiconductor interfaces by controlling the density of interface electronic states and the number of charges in the states. The density of interface states is controlled by changing the density of surface electronic states, which is controlled by surface hydrogena tion and flattening the surface atomically. We apply establishing hydr ogen termination techniques using a chemical solution, pH controlled b uffered HF or hot water, Also, slow oxidation by oxygen gas was used t o flatten resultant semiconductor surfaces. The density of interface c harges is changeable by controlling a metal work function. When the de nsity of surface states is reduced enough to unpin the Fermi level, th e barrier height is determined simply by the difference between the wo rk function of a metal phi(m) and the flat-band semiconductor phi(s)(F B). In such an interface with the law density of interface states, an ohmic contact with a zero barrier height is formed when we select a me tal with phi(m) < phi(s)(FB). We have already demonstrated controlling Schottky and ohmic properties by changing the pinning degree on silic on carbide (0001) surfaces. Further, on an atomically-flat Si(111) sur face with monohydride termination, we have observed the lowering of an Al barrier height. Moreover, we found the recovery of an ohmic proper ty after TiC formation at Ti/6H-SiC interface at 700 degrees C whereas conventional 5% HF rinsed Schottky Ti/6H-SiC interfaces still have Sc hottky properties after TiC formation.