Fully Ion Implanted Normally-Off GaN DMOSFETs with ALD-Al₂O₃ Gate Dielectrics

• Main Authors: Michitaka Yoshino, Yuto Ando, Manato Deki, Toru Toyabe, Kazuo Kuriyama, Yoshio Honda, Tomoaki Nishimura, Hiroshi Amano, Tetsu Kachi, Tohru Nakamura
• Format: Article
• Language: English
• Published: MDPI AG 2019-02-01
• Series: Materials
• Subjects: GaN; ion implantation; Mg; MOSFET; Si
• Online Access: https://www.mdpi.com/1996-1944/12/5/689
• ISSN: 1996-1944

A normally-off GaN double-implanted vertical MOSFET (DMOSFET) with an atomic layer deposition (ALD)-Al₂O₃ gate dielectric film on a free-standing GaN substrate fabricated by triple ion implantation is presented. The DMOSFET was formed with Si ion implanted source regions in a Mg ion implanted p-type base with N ion implanted termination regions. A maximum drain current of 115 mA/mm, maximum transconductance of 19 mS/mm at a drain voltage of 15 V, and a threshold voltage of 3.6 V were obtained for the fabricated DMOSFET with a gate length of 0.4 μm with an estimated p-type base Mg surface concentration of 5 × 10¹⁸ cm^−3. The difference between calculated and measured V_ths could be due to the activation ratio of ion-implanted Mg as well as Fermi level pinning and the interface state density. On-resistance of 9.3 mΩ·cm² estimated from the linear region was also attained. Blocking voltage at off-state was 213 V. The fully ion implanted GaN DMOSFET is a promising candidate for future high-voltage and high-power applications.