AlGaN/GaN metal-2DEG tunnel junction FETs with normally-off operation, high on-state current and low off-state leakage

Using conventional AlGaN/GaN HEMT structures that typically deliver normally-on (or depletion-mode) operation, a novel metal-2DEG tunnel junction FET has been successfully demonstrated. The AlGaN/GaN heterojunction delivers high-density 2DEG without any intentional doping, allowing the formation of a thin tunnel barrier with minimum impurity scattering when a Schottky contact is made to the 2DEG from the sideway. The TJ-FETs exhibit normally-off operation in an otherwise normally-on as-grown sample owing to a current controlling scheme different from that in the conventional FETs. The thickness of the tunnel barrier is controlled by the bias at an overlaying gate electrode. A positive gate bias results in a nanometer-thick barrier that leads to efficient tunnelling current, while a zero gate bias results in a thicker barrier that effectively blocks the current flow. High on-state tunnel current (326mA/mm), low off-state leakage (10^-8mA/mm) and high off-state breakdown voltage (557V) are obtained on a standard AlGaN/GaN heterostructure grown on 4-inch (111) Si substrate.