The role of AlGaN/GaN heterostructure properties in barrier height variation of Au-free ohmic contacts

Abstract

In this work, the temperature dependence of the specific contact resistance in Au-free ohmic contacts formed on AlGaN/GaN heterostructures is studied for different barrier layer characteristics, i.e. thickness and surface roughness of the AlGaN layer, and Al mole fraction. It is demonstrated that a minimum in specific contact resistance and Schottky barrier is reached with decreasing the AlGaN thickness to an optimum at which a maximum polarization field-induced carrier density ND-2DEG is formed. The Schottky barrier height at the metal/AlGaN interface is shown to be strongly linked to the heterostructure and interface properties. The dependence of the Schottky barrier height is found to be linear with Al mole fraction. The predictions from the physical interface induced gap states (IFIGS) and chemical electronegativity concepts are discussed.