Pulsed sputtering selective epitaxial formation of highly degenerate n-type GaN ohmic contacts for GaN HEMT applications

Abstract

This study describes the selective formation process of highly degenerate n-type GaN (d-GaN) ohmic contacts for the source and drain regions of GaN high electron mobility transistors (HEMTs) using pulsed sputtering deposition (PSD). The selective formation process using SiO2 masks and PSD epitaxial growth enabled the uniform formation of d-GaN in micron-meter size. The optimally formed d-GaN exhibited a minimum resistivity as low as 0.16 mΩ·cm, an electron concentration of 3.6 × 1020 cm−3, and a mobility of 108 cm2 V−1 s−1. Transmission-line-method measurements demonstrated that the contact resistance of GaN HEMTs with d-GaN regrowth contacts was remarkably low at 0.28 Ω·mm, leading to the reasonable DC output characteristics with an on-resistance of 2.8 Ω·mm and a maximum current density of 850 mA mm−1. These findings suggest that PSD epitaxial regrowth of d-GaN is a promising approach for the high-throughput formation of low-resistivity ohmic contacts on large-area GaN HEMT wafers.