Atomic layer deposited Ta2O5 gate insulation for enhancing breakdown voltage of AlN/GaN high electron mobility transistors

AlN/GaN heterostructures with a 3.5 nm AlN cap have been grown by molecular beam epitaxy followed by a 6 nm thick atomic layer deposited Ta2O5 film. Transistors fabricated with 150 nm length gates showed drain current density of 1.37 A/mm, transconductance of 315 mS/mm, and sustained drain-source biases up to 96 V while in the off-state before destructive breakdown as a result of the Ta2O5 gate insulator. Terman's method has been modified for the multijunction capacitor and allowed the measurement of interface state density (similar to 10(13) cm(-2) eV(-1)). Small-signal frequency performance of 75 and 115 GHz was obtained for f(t) and f(max), respectively. (C) 2011 American Institute of Physics. [doi:10.1063/1.3531551]