Passivation of AlGaN/GaN heterostructures with silicon nitride for insulated gate transistors

The effect of surface passivation on undoped AlGaN/GaN heterostructures using silicon nitride is presented. It is found that the charge density in the two dimensional electron gas (2DEG) at the AlGaN/GaN interface increases after passivation. This can be explained by the action of the passivating layer providing a positive charge at the AlGaN interface great enough to neutralize the AlGaN polarization charge, thereby eliminating surface related depletion from the 2DEG. A simple polarization model based on interface charges is presented to explain this enhancement, and is compared with Hall effect and capacitance voltage (C-V) measurements of passivated and unpassivated structures. The dependence of the charge enhancement on AlGaN barrier layer thickness, as well as Si₃N₄ thickness is given. We also show that a metal-insulator-semiconductor (MIS) structure of this type can be used to deplete 2DEG, allowing for the fabrication of insulated gate transistors