Enhancement-mode Polar Sourced Gallium Nitride MOSFET

Abstract

All commercially fabricated Gallium Nitride (GaN) based power transistors to date have been heterojunction field effect transistors (HFET). The major down fall of this design architecture is the inability to produce an inherently true normally-off device. The more traditional metal-oxide-semiconductor field effect transistor (MOSFET) design has the potential for power efficiency and enhancement-mode device operation. GaN has been touted as the next promising semiconductor for use in high frequency and high power applications. Various potential applications range from low frequency switching solid state transformers to inverters beyond 10 GHz frequency. These devices require high current densities, large breakdown voltages and the ability to operate in high temperature environments. Modern HFET technology has higher off-state leakage current caused from the minimum carrier density under the channel being larger than a conventional depleted GaN MOSFET. This behavior is crucial for high power applications as the off-state power consumption has become one of the essential design parameters. To date, the limiting factors of producing a GaN MOSFET are the fabrication issues associated to essential components within the MOSFET architecture; a high quality gate dielectric and a large concentration of electrons along the source and drain. As power electronic systems desire improved internal power components for next generation circuit designs, the GaN MOSFET has shown great potential over the GaN HFET based on optimized simulations and the demonstration of high quality materials. This work has characterized novel low temperature PEALD gate dielectrics with improved properties on GaN for the potential of improved GaN MOSFET characteristics. Novel ultra-thin PEALD AlN films produced high electron densities along the source and drain regions through low temperature deposition. With the incorporation of these films and conventional commercial fabrication techniques the GaN MOSFET will have a distinct impact on power electronics.