Improved oxide passivation of AlGaN/GaN high electron mobility transistors

MgO has proven effective in the past as a surface passivation layer to minimize current collapse in AlGaN/GaN high electron mobility transistors (HEMTs). However, MgO is not environmentally stable and more stable oxides need to be developed. MgCaO can be produced that is lattice matched to the GaN. Three samples were grown with 0%, 50% and 75% of Ca, which had respective lattice mismatches of -6.5% for MgO, -1% for Mg0.50Ca0.50O and +4% for Mg0.25Ca0.75O. Drain saturation current in HENTs had increases of 4.5% and 1%, respectively, for Mg0.5Ca0.5O and Mg0.25Ca0.75O passivated devices. However, there was a 10% decrease for the device passivated with pure MgO. This was due to strain applied on the nitride HEMT by the oxide, which is consistent with the piezoelectric effect in the nitride HEMT by the oxide, which is consistent with the piezoelectric effect in the nitride form the lattice mismatch between AlGaN and GaN. From pulsed measurements, HEMTs passivated with Mg0.5Ca0.5O and Mg0.25Ca0.75O showed higher passivation effectiveness (90% of dc current) then the MgO passivated HEMTs (83% dc current). This is due to the closer lattice matching of these calcium containing oxides and the reduction in interface traps associated with lattice mismatch. (C) 2005 American Institute of Physics.