Thermally robust RuOx Schottky diodes and HEMTs on III-nitrides

The potential usage of thermally robust RuOx Schottky contacts in III-nitride-based Schottky diodes and high electron mobility transistors (HEMTs) has been investigated. RuOx is deposited on nitride surface by sputtering Ru in Ar/O2 ambient. The influence of post sputtering annealing ambient and temperature on the characteristics of RuOx Schottky diodes on n-type GaN on Si(111) substrate is addressed. We also report the comparative study of thermal stability between RuOx and Ni/Au Schottky diodes on InxAl1-xN/GaN on Si(111) substrate in terms of the reverse bias leakage current and Schottky barrier height (SBH). RuOx contact shows a higher SBH of 1.24 eV and a lower leakage current of ∼10-5 Acm-2 (∼four orders of magnitude lower than that of Ni/Au) on InxAl1-xN/GaN at –40 V after annealing at 800 oC in N2. In addition, RuOx Schottky gate HEMT on InxAl1-xN/GaN on Si(111) substrate has shown a low gate leakage current of ∼6×10-8 A/mm at -8 V after annealing at 700 oC in N2 for 1 minute. The lower gate leakage current has resulted in a transistor ON/OFF current ratio of ∼105. The maximum transconductance and ON-resistance achieved by such HEMTs are about 0.18 S/mm and 8.33 Ωmm, respectively, for a gate length of 1.5 µm. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)