Off-state stress and pulse response investigation of InAl/Ga HFET

In this study In_0.18Al_0.82N/GaN HFETs were off-state tested under high drain bias, I-V characteristics were measured using standard DC voltage source (drain-source, gate-source). Subsequently drain current responses on pulse gate-source voltage for various drain-source voltages were recorded and analysed. Static performance of InAlN/GaN HFETs with AlN buffer layer prepared at different conditions were analysed before, during and after the off-state stress. The static output I-V characteristics show the maximum drain current I_d ≅ 0,44 A/mm for V_gs = 6 V, the device has pinch-off at V_gs - 4.4 V. The drain and gate currents of the InAlN/GaN HFET were measured continuously during the off-state stress (V_ds = 30 V, V_gs = -4.4 V), a partial increase of the drain/gate current was observed after this interruption, which indicates on some recovery effect. The devices were characterised in details after the total stress time of 60 min., as well as after 30 min without the stress, the output I-V characteristic show permanent off-state stress degradation. This effect will be studied in details in the next. (authors)