Thermal stability of W and WSix contacts on p-GaN

Abstract

The annealing temperature (400–1100 °C) and measurement temperature (25–300 °C) dependencies of current–voltage characteristics of W and WSi0.45 contacts on p-GaN have been compared to the more common Ni/Au metallization. At 25 °C, slightly rectifying characteristics were obtained for all three types of contact, but at 300 °C specific contact resistances in the 10−2 Ω cm2 range were obtained for WSi0.45 and Ni/Au. This is due to an increase in Mg acceptor ionization efficiency (from 10% at 25 °C to 57% at 300 °C) and more efficient thermionic hole emission across the metal-GaN interface. Both WSi0.45 and W contacts retained featureless surface morphology for annealing at >900 °C, whereas Ni/Au showed substantial islanding at ⩽700 °C.