Low-frequency-noise monitoring of current collapse in AlGaN/GaN high-electron-mobility transistors on sapphire substrate

Current collapse has been studied in unpassivated and SiN-passivated AlGaN/GaN heterostructure devices grown on a sapphire substrate by means of low-frequency-noise measurement at low temperatures, indicating this to be the most sensitive and powerful tool for assigning the deep levels in these complex and complicated structures. Generation-recombination (G-R) noise was explicitly observed in the unpassivated AlGaN/GaN heterostructure at low temperatures (T = 50-110 K) with the activation energy of 47 meV. This level was found to be dramatically decreased by the SiN passivation, from -205 dBA Hz(-1/2) down to -217 dBA Hz(-1/2), the current collapse being cured at the same time. With the SiN passivation a further G-R noise corresponding to the deeper traps of 131 and 235 meV became comparable to that corresponding to 47 meV.