Progress in novel oxides for gate dielectrics and surface passivation of GaN/AlGaN heterostructure field effect transistors

Both MgO and Sc 2 O 2 are shown to provide low interface state densities (in the 10 eV -1 cm -2 range) on n- and p-GaN, making them useful for gate dielectrics for metal-oxide semiconductor (MOS) devices and also as surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs).Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of ∼3 × 10 12 cm -2 . On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN structures are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy (40MeV) protons.