Thermal annealing behaviour of Al/Ni/Au multilayer on n-GaN Schottky contacts

Recently GaN-based high electron mobility transistors (HEMTs) haverevealed the superior properties of a high breakdown field and highelectron saturation velocity. Reduction of the gate leakage currentis one of the key issues to be solved for their further improvement.This paper reports that an Al layer as thin as 3 nm was insertedbetween the conventional Ni/Au Schottky contact and n-GaN epilayers,and the Schottky behaviour of Al/Ni/Au contact was investigatedunder various annealing conditions by current--voltage (I--V)measurements. A non-linear fitting method was used to extract thecontact parameters from the I--V characteristic curves.Experimental results indicate that reduction of the gate leakagecurrent by as much as four orders of magnitude was successfullyrecorded by thermal annealing. And high quality Schottky contactwith a barrier height of 0.875 eV and the lowest reverse-biasleakage current, respectively, can be obtained under 12 minannealing at 450°C in N₂ ambience.