Characterization of 1/f noise in GaN-based HEMTs under high dc voltage stress (Invited Paper)

We report systematic investigations on hot-electron degradation in GaN-based HEMTs with different gate recess depths, d r , fabricated by reactive ion etching. The experimental data stipulate two different mechanisms underlying the hot-electron degradations of the devices. During the initial phase of hot-electron injection significant changes were observed in the dc characteristics of the devices and the flicker noise power spectral density, SV(f).The degradations were partially recovered by annealing the devices at 100°C for 20 minutes. It is shown that for stress time ts≤25 hours the reverse bias gate current, IG, decreases systematically with ts, whereas SV(f) fluctuates randomly. Detailed analyses of SV(f) measured over a wide range temperatures show that the initial degradations originate from the percolation of carriers in the 2DEG. The significant increase in the flicker noise during the initial phase of high-voltage stress is due to the generation of H+ at the AlGaN/GaN interface. The fluctuations in the magnitudes of SV(f) for ts≤25 hours originate from the motion of the H+ in the direction of the electric field. This results in the modulation of the percolation path leading to significant variations in SV(f) as a function of ts. For ts>25 hours both IG and SV(f) are stabilized resulting from the drifting of the H+ away from the gate region. Further stressing beyond 25 hours indicate strong dependencies of the device lifetimes on dr suggesting significant material degradation due to the reactive ion etching process for the fabrication of the gate recesses. Detailed characterization of the noise show that the final irreversible degradation is due to the generation of traps at the AlGaN/GaN interface.