Potential for normally-off operation from GaN metal oxide semiconductor devices based upon semi-insulating GaN

The conditions for preparing normally-off GaN devices incorporating semi-insulating (SI) GaN materials are explored. The properties of SI GaN where carbon behaves as a deep level acceptor are predicted using a Shockley diagram. Metal-oxide-semiconductor (MOS) structures based upon these on SI-GaN layers are designed. The bandgap alignment of these structures is analyzed using Poisson equations. Normally-off operation is shown to be possible in devices featuring a thin n-GaN layer and SI-GaN layer, because of a higher conduction band energy. It is also shown that higher threshold voltage can be achieved by reducing the carrier concentration of the n-GaN channel layer.