Current instabilities and deep level investigation on AlGaN/GaN HEMT's on silicon and sapphire substrates

In this paper, we present static measurements and defect analysis performed on AlGaN/GaN/Si or Al/sub 2/O/sub 3/ HEMTs. I/sub d/-V/sub ds/-T, I/sub d/-V/sub gs/-T and I/sub g/-V/sub gs/-T characteristics show anomalies (leakage current, degradation in saturation current, Kink effect, distortions on I/sub d/-V/sub d/ characteristics in saturation region,... etc). These anomalies on output characteristics changes when we vary measurement conditions (temperature, polarisation, stress...). Deep defects analysis performed by capacitance transient spectroscopy (C-DLTS), frequency dispersion of the output conductance (G/sub ds/(f)) and random telegraph signal (RTS) prove the presence of deep defects with activations energies ranging from 0.05 eV to 1.8 eV. The presence of G-R centers acting like traps at the interface GaN/AlGaN is confirmed by I/sub g/-V/sub gs/ and RTS measurements. The localization and the identification of these defects are presented. Finally, the correlation between the anomalies observed on output characteristics and defects is discussed and a little comparison between Al/sub 2/O/sub 3/ and Si HEMTs is presented.