Improved Ohmic Contact by pre-Metallization Annealing Process in Quaternary In0.04Al0.65Ga0.31N/GaN HEMTs

Abstract

We report on the performance improvement of ohmic contact by a pre-metallization annealing process after mesa-isolation in quaternary InAlGaN/GaN high electron mobility transistors (HEMTs). By employing a pre-metallization annealing, the contact and specific contact resistances are improved from 0.31 Omega . mm and 3.67 x 10(-6) Omega cm(2) to 0.21 Omega mm and 1.63 x 10(-6) Omega cm(2), respectively. The angle-resolved X-ray photoelectron spectroscopy (AR-XPS) confirm the formation of nitrogen vacancies from the reduced atomic ratio of nitrogen and the binding energy shift of In3d(5/2), Al2p(1/2), and Ga2p(3/2) toward the higher energy after the pre-metallization annealing. Nitrogen vacancies that act as n-type dopants make the effective Schottky barrier thinner leading to the improved contact resistance. When the pre-metallization annealing process is employed to fabricate 200-nm-long gate HEMTs, the on-resistance and the maximum transconductance are improved from 1.7 Omega mm and 400 mS mm(-1) to 1.0 Omega mm and 618 mS mm(-1), respectively.