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 Ω · mm and 3.67 × 10−6 Ω cm2 to 0.21 Ω mm and 1.63 × 10−6 Ω cm2, 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 In3d5/2, Al2p1/2, and Ga2p3/2 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−1 to 1.0 Ω mm and 618 mS mm−1, respectively.