Title: Thermal Conductivity of β-Phase Ga₂O₃ and (Al_xGa_1–x)₂O₃ Heteroepitaxial Thin Films

Abstract

Heteroepitaxy of β-phase gallium oxide (β-Ga₂O₃) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of ($$\bar{2}01$$)-oriented β-Ga₂O₃ heteroepitaxial thin films were investigated. Unintentionally doped β-Ga₂O₃ thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward $$\langle$$$$11\bar{2}0$$$$\rangle$$ via metal–organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the β-Ga₂O₃ thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the β-Ga₂O₃ films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick β-Ga₂O₃ thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye–Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of β-Ga₂O₃ films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the β-Ga₂O₃ films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the β-Ga₂O₃/sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown ($$\bar{2}01$$)-oriented β-(Al_xGa_1–x)₂O₃ thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(Al_xGa_1–x)₂O₃ films exhibit lower thermal conductivities (2.8–4.7 W/m∙K) than the β-Ga₂O₃ thin films. The dominance of the alloy disorder scattering in β-(Al_xGa_1–x)₂O₃ is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown β-phase Ga₂O₃ and (Al_xGa_1–x)₂O₃ thin films and lays the groundwork for the thermal modeling and design of β-Ga₂O₃ electronic and optoelectronic devices.

Authors:

Song, Yiwen ^[1]; Ranga, Praneeth ^[2]; Zhang, Yingying ^[3]; Feng, Zixuan ^[4]; Huang, Hsien-Lien ^[4]; Santia, Marco D. ^[5]; Badescu, Stefan C. ^[5]; Gonzalez-Valle, C. Ulises  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3683-4811"

Perez, Carlos ^[1]; Ferri, Kevin ^[1]; Lavelle, Robert M. ^[1]; Snyder, David W. ^[1]; Klein, Brianna A. ^[6]; Deitz, Julia ^[6]; Baca, Albert G. ^[6]; Maria, Jon-Paul ^[1]; Ramos-Alvarado, Bladimir  ^[1];

• Search DOE PAGES for author "Ramos-Alvarado, Bladimir"
• Search DOE PAGES for ORCID "0000-0003-2573-4134"

Hwang, Jinwoo ^[4]; Zhao, Hongping  ^[4];

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• Search DOE PAGES for ORCID "0000-0002-5169-5290"

Wang, Xiaojia  ^[3]

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• Search DOE PAGES for ORCID "0000-0001-7612-1739"

more »; Krishnamoorthy, Sriram ^[2]; Foley, Brian M. ^[1]; Choi, Sukwon  ^[1]

• Search DOE PAGES for author "Choi, Sukwon"
• Search DOE PAGES for ORCID "0000-0002-3664-1542"

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+ Show Author Affiliations

1. Pennsylvania State Univ., University Park, PA (United States)
2. Univ. of Utah, Salt Lake City, UT (United States)
3. Univ. of Minnesota, Minneapolis, MN (United States)
4. The Ohio State Univ., Columbus, OH (United States)
5. Air Force Research Lab. (AFRL), Wright-Patterson AFB, OH (United States)
6. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Publication Date:

Mon Aug 09 00:00:00 EDT 2021

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); US Air Force Office of Scientific Research (AFOSR); National Science Foundation (NSF); National Resource Council (NRC)

OSTI Identifier:

1817728

Report Number(s):

SAND-2021-9937J
Journal ID: ISSN 1944-8244; 698046

Grant/Contract Number:  

NA0003525; FA9550-17-1-0141; FA9550-18-1-0507; CBET-1804840; DMR-1755479; FA9550-18-1-0479; FA9550-18RYCOR098; FA9550-18-D-0002

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 13; Journal Issue: 32; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; aluminum gallium oxide; gallium oxide; heteroepitaxy; thermal boundary conductance; thermal conductivity