Temperature Dependent Analytical Modeling, Simulation and Characterizations of HEMTs in Gallium Nitride Process

Research is being conducted for a high-performance building block for high frequency and high temperature applications that combine lower costs with improved performance and manufacturability. Researchers have focused their attention on new semiconductor materials for use in device technology to address system improvements. Of the contenders, silicon carbide (SiC), gallium nitride (GaN), and diamond are emerging as the front-runners.

GaN-based electronic devices, AlGaN/GaN heterojunction field effect transistors (HFETs), are the leading candidates for achieving ultra-high frequency and high-power amplifiers. Recent advances in device and amplifier performance support this claim. GaN is comparable to the other prominent material options for high-performance devices.

The dissertation presents the work on analytical modeling and simulation of GaN high power HEMT and MOS gate HEMT, model verification with test data and device characterization at elevated temperatures. The model takes into account the carrier mobility, the doping densities, the saturation velocity, and the thickness of different layers. Considering the GaN material processing limitations and feedback from the simulation results, an application specific AlGaN/GaN RF power HEMT structure has been proposed. The doping concentrations and the thickness of various layers are selected to provide adequate channel charge density for the proposed devices. A good agreement between the analytical model, and the experimental data is demonstrated.

The proposed temperature model can operate at higher voltages and shows stable operation of the devices at higher temperatures. The investigated temperature range is from 100⁰K to 600⁰K. The temperature models include the effect of temperature variation

on the threshold voltage, carrier mobility, bandgap and saturation velocity. The calculated values of the critical parameters suggest that the proposed device can operate in the GHz range for temperature up to 600⁰K, which indicates that the device could survive in extreme environments. The models developed in this research will not only help the wide bandgap device researchers in the device behavioral study but will also provide valuable information for circuit designers.