Photochemical Sciences Ph.D. Dissertations

Characterization of Gallium Oxide thin film grown by MOCVD

Date of Award

2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Farida Selim (Committee Chair)

Second Advisor

Howard Cromwell (Other)

Third Advisor

Joseph Furgal (Committee Member)

Fourth Advisor

Marco Nardone (Committee Member)

Fifth Advisor

Alexey Zayak (Committee Member)

Abstract

Transparent Semiconducting Oxides (TSOs) represent a special category of materials known for their unique combination of high transparency and electrical conductivity. These materials hold significant importance due to their wide range of applications, including use in electronic and optoelectronic devices such as MOSFETs, solar cells, photodiodes, gas sensors, and LEDs, among others. In recent years, Gallium Oxide (Ga2O3) has garnered substantial attention due to its promising physical and chemical properties. The most stable polymorph of Ga2O3 is known as β-Ga2O3, characterized by a relatively wide bandgap of 4.9 eV and a high breakdown voltage, making it a suitable candidate for high-power electronic devices. However, the full understanding of the optical and electrical properties of this material is still under exploration. One approach to enhancing the optical and electrical properties of β-Ga2O3 is to alloy it with another Group III metal, such as indium. This alloying process induces changes in the defect states within the material, resulting in improved film properties. Doping β-Ga2O3 with shallow donor and acceptor states is another strategy to modify the material's properties. Silicon (Si) is a commonly used donor impurity in β-Ga2O3, while magnesium (Mg) is employed to create shallow acceptor states in the material. The Metal-Organic Chemical Vapor Deposition (MOCVD) technique is employed to grow these films. Trimethylindium (TMI) serves as a precursor to alloy indium oxide with gallium oxide. For donor doping, a separate SiH4 tank is utilized, and an ion implantation process is carried out in some cases to investigate the shallow acceptor levels. Throughout this research, a specialized instrument known as Cryogenic-Thermally Stimulated Emission Spectrometry (C-TSES) is used to provide critical information about the bandgap levels of the materials. The Hall Effect method is employed to gather essential electrical properties data about the films. The findings from this study indicate that the properties of Indium Gallium Oxide (IGO) can be finely tuned to achieve various bandgap energies through alloying with indium, and the presence of shallow donor and acceptor states plays a pivotal role in shaping the optical and electrical characteristics of these materials.

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