Novel insulators for gate dielectrics and surface passivation of GaN-based electronic devices

The use of gate insulators for compound semiconductor electronics would alleviate many of the problems encountered in current Schottky based devices. Further, circuit design can be simplified since enhancement-mode MOSFETs can be used to form single supply voltage control circuits for power transistors. The use of MOSFETs also allows the use of complementary devices, thus producing less power consumption and simpler circuit design. A critical need is to develop reliable methods for deposition of these insulating films. This will enable the development of a new class of compound semiconductor electronics for high-speed communication and data processing applications. Both MgO and Sc2O3 are shown to provide low interface state densities (in the 1011 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 × 1012 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 (40 MeV) protons.