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 Al₂O₃ HEMTs. I_d-V_ds-T, I_d-V_gs-T and I_g-V_gs-T characteristics show anomalies (leakage current, degradation in saturation current, Kink effect, distortions on I_d-V_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_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_g-V_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 Al₂O₃ and Si HEMTs is presented.