High-field effects in silicon nitride passivated GaN MODFETs

This paper presents a detailed study of high-field effects in GaN MODFETs. Degradation of DC characteristics and change of flicker noise due to hot electron and high-reverse current stresses in Si/sub 3/N/sub 4/ passivated GaN MODFETs have been investigated. The authors observe that during hot electron stress, electron trapping in the barrier layer and interface state creation occur. These cause a positive shift of V/sub t/, reduce I/sub D/, skew the transfer characteristics, and degrade g/sub m/. Flicker noise (1/f) measurements show that after hot electron stress, the scaled drain current noise spectrum (S/sub I(D)//I/sub D//sup 2/) decreases in depletion, but increases only slightly in strong accumulation, corroborating the creation of interface states but only a small creation of transition-layer tunnel traps that contribute to 1/f noise. During high-reverse current stress, electron trapping dominates for the first 50-60 s and then hole trapping and trap creation begin to manifest. However, there still is net electron trapping under the gate after one hour of stress. The degradation processes bring about a positive shift of V/sub t/, degrade I/sub D/ and g/sub m/, and increase reverse leakage. After high-reverse current stress, S/sub I(D)//I/sub D//sup 2/ increases substantially in strong accumulation, indicating the creation of transition layer tunnel traps.