Photochemical Sciences Ph.D. Dissertations

Title

Growth and Characterization of Wide Band-Gap Group III Oxide Semiconductors by MOCVD

Date of Award

2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Farida Selim (Advisor)

Second Advisor

Marco Nardone (Committee Member)

Third Advisor

Alexander Tarnovsky (Committee Member)

Fourth Advisor

Ellen Grosevski (Other)

Abstract

This dissertation work is focused on the deposition of gallium oxide (Ga2O3) thin films by metal organic chemical vapor deposition (MOCVD) method. This material belongs to a special group of wide bandgap oxide semiconductors with high optical transmittance and high levels of conductivity. The importance of this material is generated by the wide range of applications of electronic and optoelectronic devices such as MOSFET’s, photo diodes, solar cells, LED’s, laser diodes, sensors etc. Through MOCVD technique, an implementation of a Si4+ dopant was incorporated in the monoclinic β-Ga2O3 crystal structure on homoepitaxial and heteroepitaxial β-Ga2O3 single crystal wafers. The MOCVD process allowed us to deposit at a growth rate of 1 μm/hour while controlling the electrical transport properties with this dopant. These films were carefully characterized by surface morphology, crystal structure, levels of conductivity and trapping defects. The work shows that the electron density and conductivity of MOCVD Ga2O3 films are mainly governed by the interplay between dopant concentration, C concentration and the presence of trapping defects in the films, which is most likely applicable for other oxide films grown by MOCVD. Conductive films of Ga2O3 with resistivity in the order of 0.07 Ω.cm were successfully grown. The electron density in most of these films was in the range of 1019 cm−3 but the mobility was limited to 1.5 cm2/V⋅s. Higher mobility of 30 cm2/V⋅s was obtained in some films at the expense of carrier concentration by reducing Si doping level resulting in resistivity in the order of 0.3 Ω.cm. This range of conductivity and mobility is relevant for field-effect transistors (FET) and the applications of Ga2O3 as transparent FET in Deep Ultra-Violet (DUV) technology. The second part of this work focuses on investigating the electronic and crystal structure properties of an indium gallium oxide alloy (IGO) doped with Si4+ ions through MOCVD technique on c-sapphire substrate. This work aims to find a tunable range for engineering the band gap of this new alloyed material by incorporating indium into the lattice of the β-Ga2O3 crystal structure. Various dopant ratios were also implemented to adjust the electrical properties of (IGO) and highly conductive IGO films were realized through Si doping.

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