Schottky-Barrier Normally Off GaN/InAlN/AlN/GaN HEMT With Selectively Etched Access Region

A Schottky-barrier normally off InAlN-based high-electron-mobility transistor (HEMT) with selectively etched access regions, high OFF-state breakdown, and low gate leakage is presented. Metal-organic chemical vapor deposition-grown 1-nm InAlN/1-nm AlN barrier stack is capped with a 2-nm-thick undoped GaN creating a negative polarization charge at a GaN/InAlN heterojunction. Consequently, the gate effective barrier height is increased, and the gate leakage as well as the equilibrium carrier concentration in the channel is decreased. After removal of the GaN cap at access regions by using a highly selective dry process, the extrinsic channel becomes populated by carriers. Normally off HEMTs with 8-mu m source-to-drain distance and 1.8-mu m-long symmetrically placed gate showed a source drain current of about 140 mA/mm. The HEMT gate leakage at a drain voltage of 200 V and grounded gate is below 10(-7) A/mm with a three-terminal device breakdown of 255 V. The passivated InAlN surface potential has been calculated to be 1.45 V; significant drain current increase is predicted for even lower potential.