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.
","abstract_html":"<p><em>β</em>-Ga<sub>2</sub>O<sub>3</sub> 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. <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> can be grown as thin films or as large single crystals by melt growth-techniques, which is important for scalable manufacturing. However, <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> suffers from a lack of <em>p</em>-type dopants and a low thermal conductivity. Presently, all applications are based on <em>n</em>-type <em>β</em>-Ga<sub>2</sub>O<sub>3</sub>; the introduction of <em>p</em>-type <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> would enable bipolar power devices. Additionally, high-power switching results in elevated temperatures where heat retention can impede electronic performance.</p> <p>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 <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> to a level at which <em>p</em>-type doping is achievable, and (2) the possibility of improving the thermal properties of <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> by alloying with the lightest Group-13 cation, B.</p> <p>We find that doping with Bi creates mid-gap states derived from the Bi 6<em>s</em> electrons at similar energy level to candidate acceptors through an anti-bonding hybridization of the Bi lone pair with the O 2<em>p</em> states. The associated states are more dispersed than the pristine valence band, as they derive from the delocalized <em>s</em>-states of Bi rather than the <em>p</em>-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 <em>p</em>-type dopants.</p> <p>We explored several pathways to include B as an alloy in <em>β</em>-Ga<sub>2</sub>O<sub>3</sub>, 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 <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> in favor of a flat triangular coordination, as observed in B<sub>2</sub>O<sub>3</sub>. We conclude that B is likely insoluble in <em>β</em>-Ga<sub>2</sub>O<sub>3</sub> at concentrations high enough to substantively improve its thermal conductivity.</p>","abstract_has_math":false,"creators":["Tattersfield, Ben"],"institution":null,"degree_name":"Master of Science (MS)","degree_level":"Thesis","degree_discipline":"Materials Science & Engineering","degree_department":null,"school":null,"contributors":["Rohan Mishra","Katharine Flores Chuan Wang"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-08-13T07:00:00Z","date_published":"2020-08-13T07:00:00Z","updated_at":"2026-07-24T06:13:31Z","subjects":["Ga2O3","Gallium Oxide","DFT","Alloying","Engineering"],"languages":["English (en)"],"rights":["I have not registered my thesis with the U.S. Copyright Office, and do not intend to."],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://openscholarship.wustl.edu/eng_etds/558"],"render_values":[{"text":"https://openscholarship.wustl.edu/eng_etds/558","href":"https://openscholarship.wustl.edu/eng_etds/558","code":true}]}]},"links":{"outbound_url":"https://doi.org/10.7936/8qn5-0n90","outbound_label":"DOI","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Rohan Mishra","Katharine Flores Chuan Wang"]},{"key":"dc:creator","label":"Author","values":["Tattersfield, Ben"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2020-09-02T07:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science & Engineering","McKelvey School of Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science (MS)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Ga2O3","Gallium Oxide","DFT","Alloying","Engineering"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English (en)"]},{"key":"dc:rights","label":"Dc Rights","values":["I have not registered my thesis with the U.S. Copyright Office, and do not intend to."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://doi.org/10.7936/8qn5-0n90","https://openscholarship.wustl.edu/eng_etds/558"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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.
"]},{"key":"dc:title","label":"Title","values":["First-Principles Investigation of Doping and Alloying of β-Ga2O3"]}]}],"canonical_facts":{"dc:contributor":["Rohan Mishra","Katharine Flores Chuan Wang"],"dc:creator":["Tattersfield, Ben"],"dc:date.available":["2020-09-02T07:00:00Z"],"dc:description.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.
"],"dc:identifier":["https://doi.org/10.7936/8qn5-0n90","https://openscholarship.wustl.edu/eng_etds/558"],"dc:language":["English (en)"],"dc:rights":["I have not registered my thesis with the U.S. Copyright Office, and do not intend to."],"dc:subject":["Ga2O3","Gallium Oxide","DFT","Alloying","Engineering"],"dc:title":["First-Principles Investigation of Doping and Alloying of β-Ga2O3"],"thesis:degree_discipline":["Materials Science & Engineering","McKelvey School of Engineering"],"thesis:degree_level":["Thesis"],"thesis:degree_name":["Master of Science (MS)"]},"updated_at":"2026-07-24T06:13:31Z"}