Vertical GaN Trench‐MOSFETs Fabricated on Ammonothermally Grown Bulk GaN Substrates

Herein, the fabrication and characterization of vertical GaN trench‐MOSFETs on ammonothermally grown bulk GaN substrates have been reported. A number of technological processes have been developed, including, among others, low‐resistance ohmic contacts to Ga‐face n‐GaN epitaxial layers, N‐face backside ohmic contact, vertical sidewall trench etching processes, surface preparation, and atomic layer deposition of gate dielectric layers and integrated with fabrication process flow of vertical power devices. The fabricated test structures are characterized by an output drain current of 288 ± 74 mA mm−1, threshold voltage of about 10 V, and field‐effect channel mobility 13.1 ± 5.0 cm2 (Vs)−1 at 10 V drain‐source voltage and up to 65 cm2 (Vs)−1 at 0.1 V drain‐source voltage. In addition, first, experiments toward high current multicell transistor fabrication are carried out. Multicell test devices with hexagonal topology with a total gate width of 11.1 mm and output current over 1 A are successfully fabricated and characterized.