Improved Ohmic Contact by Pre‐Metallization Annealing Process in Quaternary In_0.04Al_0.65Ga_0.31N/GaN HEMTs

Abstract

We report on the performance improvement of ohmic contact by a premetallization annealing process after mesa-isolation in quaternary InAlGaN/ GaN high electron mobility transistors (HEMTs). By employing a premetallization annealing, the contact and specific contact resistances are improved from 0.31 Ω Á mm and 3.67 Â 10 À6 Ω cm 2 to 0.21 Ω mm and 1.63 Â 10 À6 Ω 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 Ω mm and 400 mS mm À1 to 1.0 Ω mm and 618 mS mm À1 , respectively.