Complete analytical model of GaN MESFETs for high power and Microwave frequency applications

Abstract

In the past few years, growing interest has been paid to the wide band gap materials such as GaN because of its low thermal generation rate and high breakdown field for its potential use in high power, high temperature and microwave frequency applications. The use of GaN based devices for efficient, linear high power RF amplifiers has already been grown for military applications. GaN Metal Semiconductor Field Effect Transistors (MESFETs) have received much attention as its structure is simpler to analyze than that of High Electron Mobility Transistors (HEMTs) and its epi-layers and the physical effects are easier to realize and interpret. Flourishing interest in exploiting the properties and performance of GaN based devices requires the development of simple physics-based analytical models to simplify the device parameter acquisition and to be able to use it for computer-aided design of GaN integrated circuits (ICs). Few analytical models on GaN MESFETs are reported, though significant experimental work is available. Therefore more analytical models should be developed to understand the device operation accurately. In this thesis, analytical one- and two-dimensional channel potential models are developed for long-channel GaN MESFETs based on the solution of Poisson’s equation. The developed analytical channel potential model can be used for short-channel MESFETs with some modifications and assumptions. Analytical models for I-V and C-V characteristics of GaN MESFET are also presented considering the effect of parasitic resistances and gate length modulation. The models evaluate the transconductance and optimum noise figure. The models developed in this thesis will be very helpful to understand the device behaviour in nanometer regime for future applications.