Mechanisms of Schottky Barrier Control on n-Type Germanium Using Ge3N4 Interlayers

The influence of a few monolayers of crystalline and amorphous Ge3N4 on the Schottky barrier height of n-type Ge has been investigated. Low temperature capacitance-voltage measurements are used to accurately determine the barrier height. Both amorphous and epitaxial Ge3N4 effectively eliminate pinning of the Fermi level at the metal/Ge interface. Metal/Ge3N4/n-Ge contacts therefore show a linear dependence of the Schottky barrier height with metal work function. Our results indicate that the Fermi level unpinning is achieved mainly due to the passivation of interface states related to defects at the metal/Ge interface. Aluminum on amorphous and epitaxial Ge3N4 delivers barrier heights of 0.09+/-0.05 and 0.0+/-0.1 eV, respectively, resulting in Ohmic behavior. The formation of epitaxial Ge3N4 requires temperatures above 600 degrees C, whereas amorphous layers can be formed at much lower temperatures. Amorphous Ge3N4 can therefore be used to form Ohmic contacts at a low thermal budget. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3545703] All rights reserved.