Time-dependent RF performance degradation modeling of AlGaN/GaN HFETs

High voltage HFETpsilas fabricated from the AlGaN/GaN heterojunction demonstrate excellent RF output power performance. The nitride HFETpsilas produce RF output power greater than an order of magnitude higher than available from GaAs and InP based devices. However, the HFETs demonstrate a reliability problem where the dc current and RF output power continually decrease as a function of time. The reliability problem is shown to be related to the conduction characteristics of the gate electrode and an electron tunneling mechanism where electrons leak from the gate to the surface of the semiconductor. In this work the physics responsible for this behavior are investigated and described. Physics-based models suitable for use in RF circuit harmonic-balance simulators have been developed, with excellent agreement between measured and simulated data.