Low-resistivity V/Al/Mo/Au ohmic contacts on AlGaN/GaN annealed at low temperatures

Abstract

We investigated the electrical characteristics of V/Al/Mo/Au ohmic contacts on AlGaN/GaN heterostructure field effect transistors (HFETs). A minimum ohmic contact resistivity of 1.6 × 10-6 Ωcm2 was achieved after annealing at 550 °C by optimizing V thickness to 15 nm. Crosssectional transmission electron microscope (TEM) images exhibited a large difference in the extent of metal reaction between V/Al/Mo/Au and Ti/Al/Mo/Au. In addition to their lower contact resistivities, the low-temperature annealed V/Al/Mo/Au ohmic contacts exhibited better characteristics, such as enhanced breakdown voltages by about 100 V and smooth surface morphology, than the Ti/Al/Mo/Au ohmic contact annealed at the optimum annealing temperature. © 2010 The Japan Society of Applied Physics.