Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Electrical Engineering

Major Professor

Syed K. Islam

Committee Members

Benjamin J. Blalock, Leon M. Tolbert, Mohamed R. Mahfouz


With the most advanced and mature technology for electronic devices, silicon (Si) based devices can be processed with practically no material defects. However, Si technology has difficulty meeting the demand for some high-power, high-speed, and high-temperature applications due to limitations in its intrinsic properties. Wide bandgap semiconductors have greater prospects compared to Si based devices. The wide band gap material system shows higher breakdown voltage, lower leakage, higher saturation velocity, larger thermal conductivity and better thermal stability suitable for high-power, high-speed, and high-temperature operations of the devices. In recent years, GaN based devices have drawn much research attention due to their superior performances compared to other wide bandgap semiconductor (SiC) devices. Specifically, implementation of AlGaN/GaN high electron mobility transistor (HEMT) based power amplifiers have become very promising for applications in base stations or radar. With the increase in device power, channel temperature rises. This introduces high-temperature effects in the device characteristics. In addition, high-power, high-frequency and high-temperature operation of AlGaN/GaN HEMT is required for telemetry in extreme environment.

AlGaN/GaN HEMT also shows great potential as chemically selective field-effect transistor (CHEMFET). Due to simpler imprint technique and amplification advantages CHEMFET based detection and characterization of bio-molecules has become very popular. AlGaN/GaN HEMT has high mobility two-dimensional electron gas (2 DEG) at the hetero-interface closer to the surface and hence it shows high sensitivity to any surface charge conditions.

The primary objective of this research is to develop a temperature dependent physics based model of AlGaN/GaN HEMT to predict the performance for high-power and high- speed applications at varying temperatures. The physics based model has also been applied to predict the characteristics of AlGaN/GaN HEMT based CHEMFET for the characterization of bio-molecular solar batteries - Photosystem I reaction centers. Using the CHEMFET model, the number of reaction centers with effective orientation on the gate surface of the HEMT can be estimated.

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