Novel dielectrics for gate oxides and surface passivation on GaN

Abstract

We review recent progress in obtaining low interface state densities on GaN and reducing current collapse with dielectrics on AlGaN/GaN high electron mobility transistors (HEMTs). New oxides of scandium and magnesium have shown promise for surface passivation on HEMTs however the lattice mismatches of −6.5% for MgO and +9.1% for Sc 2O 3 have led to efforts to find lower lattice mismatch oxides to increase oxide/nitride interfacial stability. By adding calcium to MgO, a crystalline film of MgCaO can be produced that has a closer lattice match to GaN. Stability of the dielectric films was determined for environmental and thermal processes and a 5 nm cap of Sc 2O 3 was found to increase the stability of the MgCaO over that of MgO and produce a 15% increase in carrier concentration over the non-passivated samples. This increase in sheet carrier density was maintained for several weeks at temperatures of 200 °C.