Normally-off vertical-type mesa-gate GaN MOSFET

A vertical-type mesa-gate GaN metal-oxide semiconductor field-effect transistor (MOSFET) has been fabricated. The mesa-gate structure can be easily achieved by a single deep etch to the n⁺-GaN which is the drain of the device, whereas the trench-gate structure, the commonly used structure for the vertical-type MOSFETs, requires an additional etching process to define the gate region. The mesa-gate GaN MOSFET exhibited a normally-off operation with the threshold voltage of 3 V, a normalised drain current of ~ 55 mA/mm and a high on/off current ratio of 10⁸.