Hot carrier aging degradation phenomena in GaN based MESFETs

Abstract

Schottky contacts of Pt and Ir on undoped Al0.36Ga0.64N have been fabricated and the ideality factor, the built-in voltage and the reverse bias current were determined using current–voltage measurements to make a comparison.The smallest ideality factors, the lowest reverse bias current and the highest built-in voltages have been obtained for Ir Schottky contacts.We have studied the effect of an annealing for Pt and Ir Schottky contacts, on the ideality factor, the built-in voltage and the reverse bias current. A decrease of the ideality factor and the reverse bias current associated to an increase of the built-in voltage have been obtained except for high annealing temperature (T > 400 °C).Reductions of 37% and 43% of the ideality factor and improvements of 24% and 41% of the built-in voltage have been obtained for Pt and Ir Schottky contacts, respectively, after an annealing performed at 350 °C during 30 min.Two different electrical stresses have also been applied on the ohmic and Schottky contacts during 164 h to study the reliability of the employed technology. In a first time, the devices have been stressed with a drain-to-source voltage VDS of 20 V and a gate-to-source voltage VGS of −5 V to submit the devices to an electrical field only and not to a thermal effect induced by the electrical current. In a second time, the aging stress has been applied for a VDS of 20 V and for a VGS of 0 V in order to study the impact of the electrical field and the thermal effect induced by the drain current on the electrical behaviours of Al0.36Ga0.64N/GaN transistors. This study has also shown the existence of electrical traps in the device structure and proved the good reliability of the involved technology.These comparative studies demonstrate that Ir is a better candidate than Pt for the realisation of Schottky contacts on undoped Al0.36Ga0.64N.