Reliability Modeling of High Voltage AlGaN/GaN and GaAs Field-Effect Transistors

摘要

High voltage HFET's fabricated from nitride semiconductors utilizing the AlGaN/GaN heterojunction or GaAs using field plates demonstrate excellent RF output power performance. The nitride HFET's produce RF output power greater than an order of magnitude higher than available from GaAs and InP based devices, and GaAs FET's fabricated with field-plates can produce RF output power about a factor of two greater than standard FET's. However, the FET's demonstrate a reliability problem where the dc current and RF output power continually decrease as a function of time. The problem is more serious in the nitride HFET's, although both nitride-based and GaAs-based devices suffer reliability problems. The reliability problem is 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. Design techniques to reduce the reliability problem will be discussed.