Comparative study of the optical properties of α-, β-, and κ-Ga2O3

Lewis T. Penman; Zak M. Johnston; Paul R. Edwards; Yuichi Oshima; Clifford McAleese; Piero Mazzolini; Matteo Bosi; Luca Seravalli; Roberto Fornari; Robert W. Martin; Fabien C.-P. Massabuau

doi:10.1002/pssb.202400615

Comparative study of the optical properties of α-, β-, and κ-Ga2O3

Lewis T. Penman^*, Zak M. Johnston, Paul R. Edwards, Yuichi Oshima, Clifford McAleese, Piero Mazzolini, Matteo Bosi, Luca Seravalli, Roberto Fornari, Robert W. Martin, Fabien C.-P. Massabuau

^*Corresponding author for this work

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Abstract

A systematic investigation of the optical properties of β‐, α‐, and κ‐phase gallium oxide (Ga2O3) polymorphs is conducted by UV–vis spectrophotometry through the Swanepoel method and temperature‐dependent photoluminescence. Using the same approach and apparatus allows similarities and differences between these three phases to be directly established. Differences between polymorphs are observed, including refractive indices of 1.89 (β), 2.00 (α), and 1.85 (κ) and optical bandgaps of 4.99 eV (β), 5.32 eV (α), and 4.87 eV (κ). In the luminescence studies, four emission peaks in each polymorph are revealed, located at different energies in the UV (3.1–3.9 eV), blue (2.7–3.0 eV), and green (2.2–2.6 eV) regions, with causes attributed to self‐trapped holes, donor–acceptor pair transitions involving Ga and O vacancies (VGa, VO), Ga O divacancies (VGa + VO), O interstitials (Oi), and H impurities (VGa–nH, Hi, Ho). In this systematic study, unique optical properties of the different Ga2O3 polymorphs are highlighted and it is warned that the commonly practiced analogy to β‐Ga2O3 can lead to misinterpretations.

Original language	English
Number of pages	8
Journal	Physica Status Solidi B
Early online date	12 Feb 2025
DOIs	https://doi.org/10.1002/pssb.202400615
Publication status	E-pub ahead of print - 12 Feb 2025

Funding

The authors acknowledge support from the Engineering and Physical Sciences Research Council (EP/W524670/1, EP/V034995/1), and from the Rank Prize Undergrad Vacation scholarship. MB and RF acknowledge the financial support from PNRR-M4C2- I1.1 – Funded by the European Union-NextGenerationEU; Italian Ministry of University and Research Call for proposals n.104 of 02-02-2022-PRIN2022-ERC sector PE3 Project title: UV-C Sensors based on Gallium Oxide (USE GAO)-Project Code 2022A4AN2F-CUP CodeD53D23002180006; Grant decree No. 2022A4AN2F dated 28/09/2023. The authors would also like to thank Indraneel Sanyal, Andrew Pakes, and Stuart Semple for their contributions to this work.

Keywords

gallium oxide
wide-bandgap
transmittance
photoluminescence
polymorph
semiconductors

Access to Document

10.1002/pssb.202400615Licence: CC BY 4.0

Penman-etal-PSSB-2025-Comparative-study-of-the-optical-propertiesFinal published version, 1.3 MBLicence: CC BY 4.0

DTP 2224 University of Strathclyde | Penman, Lewis
Massabuau, F. (Principal Investigator), Martin, R. (Co-investigator) & Penman, L. (Research Co-investigator)
EPSRC (Engineering and Physical Sciences Research Council)
1/04/23 → 1/10/26
Project: Research Studentship - Internally Allocated
UV-Vis Spectrophotometer (with integrated sphere) - Shimadzu UV-2600
Massabuau, F. (Principal Investigator)
16/02/21 → …
Project: Equipment only
Photoluminescence setup JA2.02A - 224 nm laser (Photon System HeAg 70-224SL)
Massabuau, F. (Principal Investigator)
21/01/21 → …
Project: Equipment only

Data for: "Comparative study of the optical properties of α-, β-, and κ-Ga₂O₃"
Penman, L. (Creator) & Massabuau, F. (Supervisor), University of Strathclyde, 3 Feb 2025
DOI: 10.15129/61b028bc-643b-42ea-b55c-4f86b5ba56ca
Dataset

EPSRC Capital Core Equipment Award 2020
Massabuau, F. (Recipient), 2020
Prize: Other distinction

Cite this

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title = "Comparative study of the optical properties of α-, β-, and κ-Ga2O3",

abstract = "A systematic investigation of the optical properties of β‐, α‐, and κ‐phase gallium oxide (Ga2O3) polymorphs is conducted by UV–vis spectrophotometry through the Swanepoel method and temperature‐dependent photoluminescence. Using the same approach and apparatus allows similarities and differences between these three phases to be directly established. Differences between polymorphs are observed, including refractive indices of 1.89 (β), 2.00 (α), and 1.85 (κ) and optical bandgaps of 4.99 eV (β), 5.32 eV (α), and 4.87 eV (κ). In the luminescence studies, four emission peaks in each polymorph are revealed, located at different energies in the UV (3.1–3.9 eV), blue (2.7–3.0 eV), and green (2.2–2.6 eV) regions, with causes attributed to self‐trapped holes, donor–acceptor pair transitions involving Ga and O vacancies (VGa, VO), Ga O divacancies (VGa + VO), O interstitials (Oi), and H impurities (VGa–nH, Hi, Ho). In this systematic study, unique optical properties of the different Ga2O3 polymorphs are highlighted and it is warned that the commonly practiced analogy to β‐Ga2O3 can lead to misinterpretations.",

keywords = "gallium oxide, wide-bandgap, transmittance, photoluminescence, polymorph, semiconductors",

author = "Penman, {Lewis T.} and Johnston, {Zak M.} and Edwards, {Paul R.} and Yuichi Oshima and Clifford McAleese and Piero Mazzolini and Matteo Bosi and Luca Seravalli and Roberto Fornari and Martin, {Robert W.} and Massabuau, {Fabien C.-P.}",

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doi = "10.1002/pssb.202400615",

language = "English",

journal = "Physica Status Solidi B",

issn = "0370-1972",

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T1 - Comparative study of the optical properties of α-, β-, and κ-Ga2O3

AU - Penman, Lewis T.

AU - Johnston, Zak M.

AU - Edwards, Paul R.

AU - Oshima, Yuichi

AU - McAleese, Clifford

AU - Mazzolini, Piero

AU - Bosi, Matteo

AU - Seravalli, Luca

AU - Fornari, Roberto

AU - Martin, Robert W.

AU - Massabuau, Fabien C.-P.

PY - 2025/2/12

Y1 - 2025/2/12

N2 - A systematic investigation of the optical properties of β‐, α‐, and κ‐phase gallium oxide (Ga2O3) polymorphs is conducted by UV–vis spectrophotometry through the Swanepoel method and temperature‐dependent photoluminescence. Using the same approach and apparatus allows similarities and differences between these three phases to be directly established. Differences between polymorphs are observed, including refractive indices of 1.89 (β), 2.00 (α), and 1.85 (κ) and optical bandgaps of 4.99 eV (β), 5.32 eV (α), and 4.87 eV (κ). In the luminescence studies, four emission peaks in each polymorph are revealed, located at different energies in the UV (3.1–3.9 eV), blue (2.7–3.0 eV), and green (2.2–2.6 eV) regions, with causes attributed to self‐trapped holes, donor–acceptor pair transitions involving Ga and O vacancies (VGa, VO), Ga O divacancies (VGa + VO), O interstitials (Oi), and H impurities (VGa–nH, Hi, Ho). In this systematic study, unique optical properties of the different Ga2O3 polymorphs are highlighted and it is warned that the commonly practiced analogy to β‐Ga2O3 can lead to misinterpretations.

AB - A systematic investigation of the optical properties of β‐, α‐, and κ‐phase gallium oxide (Ga2O3) polymorphs is conducted by UV–vis spectrophotometry through the Swanepoel method and temperature‐dependent photoluminescence. Using the same approach and apparatus allows similarities and differences between these three phases to be directly established. Differences between polymorphs are observed, including refractive indices of 1.89 (β), 2.00 (α), and 1.85 (κ) and optical bandgaps of 4.99 eV (β), 5.32 eV (α), and 4.87 eV (κ). In the luminescence studies, four emission peaks in each polymorph are revealed, located at different energies in the UV (3.1–3.9 eV), blue (2.7–3.0 eV), and green (2.2–2.6 eV) regions, with causes attributed to self‐trapped holes, donor–acceptor pair transitions involving Ga and O vacancies (VGa, VO), Ga O divacancies (VGa + VO), O interstitials (Oi), and H impurities (VGa–nH, Hi, Ho). In this systematic study, unique optical properties of the different Ga2O3 polymorphs are highlighted and it is warned that the commonly practiced analogy to β‐Ga2O3 can lead to misinterpretations.

KW - gallium oxide

KW - wide-bandgap

KW - transmittance

KW - photoluminescence

KW - polymorph

KW - semiconductors

U2 - 10.1002/pssb.202400615

DO - 10.1002/pssb.202400615

M3 - Article

SN - 0370-1972

JO - Physica Status Solidi B

JF - Physica Status Solidi B

ER -

Comparative study of the optical properties of α-, β-, and κ-Ga2O3

Abstract

Funding

Keywords

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Projects

DTP 2224 University of Strathclyde | Penman, Lewis

UV-Vis Spectrophotometer (with integrated sphere) - Shimadzu UV-2600

Photoluminescence setup JA2.02A - 224 nm laser (Photon System HeAg 70-224SL)

Datasets

Data for: "Comparative study of the optical properties of α-, β-, and κ-Ga₂O₃"

Prizes

EPSRC Capital Core Equipment Award 2020

Cite this