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 SiO _2 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 × 10 ^20 cm ^−3 , and a mobility of 108 cm ^2 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.