Impact of ALD Gate Dielectrics (SiO2, HfO2, and SiO2/HAH) on Device Electrical Characteristics and Reliability of AlGaN/GaN MOSHFET Devices

GaN/AlGaN metal oxide semiconductor heterojunction field effect transistors (MOSHFET) with various gate dielectrics have been fabricated and studied. It was found that gate oxides formed by atomic layer deposition (ALD) provides improved device electrical characteristics over the conventional SiO2 formed by PECVD method. It was also found that there is no additional Ga oxide growth during the ALD process resulting in good and smooth interface. Conductance measurements showed that the trap state density is reduced with ALD dielectrics as compared to Schottky HFET device. Stacked dielectrics can provide large gate over drive voltage enabling low on-state resistance and high drain current