Abstract
β-Ga2O3 is an emergent semiconductor for power electronics applications. It has a wide band gap of 4.8 eV and is transparent on the whole spectrum of visible light up to deep ultraviolet. It has a high Baliga figure of merit (BFOM) — a weighted numerical combination of the dielectric constant, charge carrier mobility, and critical breakdown field —, which is commonly used for a quantitative comparison of semiconductors for high-current operation and power switching applications. β-Ga2O3 can be grown as thin films or as large single crystals by melt growth-techniques, which is important for scalable manufacturing. However, β-Ga2O3 suffers from a lack of p-type dopants and a low thermal conductivity. Presently, all applications are based on n-type β-Ga2O3; the introduction of p-type β-Ga2O3 would enable bipolar power devices. Additionally, high-power switching results in elevated temperatures where heat retention can impede electronic performance.
The objective of this thesis is to investigate, using first-principles density-functional-theory calculations: (1) the efficiency of doping with Bi to raise the valence band of β-Ga2O3 to a level at which p-type doping is achievable, and (2) the possibility of improving the thermal properties of β-Ga2O3 by alloying with the lightest Group-13 cation, B.
We find that doping with Bi creates mid-gap states derived from the Bi 6s electrons at similar energy level to candidate acceptors through an anti-bonding hybridization of the Bi lone pair with the O 2p states. The associated states are more dispersed than the pristine valence band, as they derive from the delocalized s-states of Bi rather than the p-states of highly electronegative O, which dominate the valence band. Our calculations indicate that these intermediate states are natively filled, and at an appropriate energy level to use a co-dopant like Mg, N, or even native Ga vacancies as p-type dopants.
We explored several pathways to include B as an alloy in β-Ga2O3, including the high-entropy alloy (HEA) approach and a variety of ordered binary and ternary alloys. Despite these efforts, we do not find a stable alloy, since the small B atoms reject the octahedral and tetrahedral coordination of the cations in β-Ga2O3 in favor of a flat triangular coordination, as observed in B2O3. We conclude that B is likely insoluble in β-Ga2O3 at concentrations high enough to substantively improve its thermal conductivity.
Committee Chair
Rohan Mishra
Committee Members
Katharine Flores Chuan Wang
Degree
Master of Science (MS)
Document Type
Thesis
Date of Award
Summer 8-13-2020
Language
English (en)
Recommended Citation
Tattersfield, Ben, "First-Principles Investigation of Doping and Alloying of β-Ga2O3" (2020). McKelvey School of Engineering Theses & Dissertations. 558.
The definitive version is available at https://doi.org/10.7936/8qn5-0n90