Surface Leakage Currents in SiN and Al_2O_3 Passivated AlGaN/GaN High Electron Mobility Transistors

Surface leakage currents of AlGaN/GaN high electron mobility transistors are investigated by utihzing a circular double-gate structure to eliminate the influence of mesa leakage current.Different mechanisms are found under various passivation conditions.The mechanism of the surface leakage current with Al_2O_3 passivation follows the two-dimensional variable range hopping model,while the mechanism of the surface leakage current with SiN passivation follows the Frenkel-Poole trap assisted emission.Two trap levels are found in the trap-assisted emission.One trap level has a barrier height of 0.22 eV for the high electric Geld,and the other trap level has a barrier height of 0.12 eV for the low electric field.