Session:

Gallium oxide (Ga₂O₃) is a very promising material that belongs to the novel class of ultra-wide bandgap semiconductors exhibiting such unique features as very high electric field breakdown, acceptable electron mobility, low-cost fabrication process, etc. However, there is a fundamental limitation of Ga₂O₃ attributed to its low thermal conductivity [1]. Therefore, effective thermal energy management is crucial for the further development of Ga₂O₃ technology.
Up to now, most of the studies on Ga₂O₃ were focused on its conventional monoclinic β-phase due to its high stability, but thermal management is not limited just to this phase and there is a strong interest to explore properties of other phases [2]. The second most studied structure is corundum α-Ga₂O₃, but it is a metastable phase that converts to monoclinic β-phase at high temperatures (~650°C) [3]. Most recently it was demonstrated that ion implantation can result in the formation of highly oriented new Ga₂O₃polymorph on the top of β-phase having sharp polymorph interfaces. This new phase was identified as orthorhombic κ-Ga₂O₃ [4] or defective cubic spinel γ-Ga₂O₃[5]. Moreover, there is a strong demand to study the properties of phase-transformed interfaces, particularly thermal transport as it has a great impact on device performance. To the best of our knowledge, there is also no information from the literature neither on the thermal properties of κ- or γ-Ga₂O₃, nor on interfacial thermal conductance across phase-transformed interfaces, nor on phonon transport in ion beam-modified Ga₂O₃materials.
In this work, we study the phonon thermal transport in [010] oriented β-Ga₂O₃ irradiated by 500 keV, 1 MeV, and 1.7 MeV Ga ions to a fluence of 6×10¹⁵ ions/cm². X-ray diffraction and Rutherford backscattering spectrometry techniques reveal a radiation-induced phase transformation in the implanted region. Heat transport measurements were performed using a femtosecond laser-based frequency-modulated time-domain thermoreflectance (TDTR). By controlling the penetration depth of the thermal waves using different modulation rates, we could spatially probe two different regions: first was several hundred nanometer-thick new phase and damaged β-phase. The thickness of the new phase was estimated to be in excellent agreement with the Rutherford backscattering technique, therefore demonstrating the capability of TDTR to spatially isolate the conductivities of individual phases. To validate the experimental results, the density functional theory was implemented to predict the thermal conductivity of the emerging κ-phase.
This work was supported by Nazarbayev University collaborative research program (CRP) grant 11022021CRP1504. M-ERA.NET GOFIB project (RCN project number 337627) is also acknowledged for financial support.
References:
1) Reese, S. B., Remo, T., Green, J., & Zakutayev, A. (2019). How much will gallium oxide power electronics cost?. Joule, 3(4), 903-907. https://doi.org/10.1016/j.joule.2019.01.011
2) Furthmüller, J., & Bechstedt, F. (2016). Quasiparticle bands and spectra of Ga 2 O 3 polymorphs. Physical Review B, 93(11), 115204. https://doi.org/10.1103/PhysRevB.93.115204.
3) Pearton, S. J., Yang, J., Cary IV, P. H., Ren, F., Kim, J., Tadjer, M. J., & Mastro, M. A. (2018). A review of Ga2O3 materials, processing, and devices. Applied Physics Reviews, 5(1), 011301. https://doi.org/10.1063/1.5006941.
4) Azarov, A., Bazioti, C., Venkatachalapathy, V., Vajeeston, P., Monakhov, E., & Kuznetsov, A. (2022). Disorder-induced ordering in gallium oxide polymorphs. Physical Review Letters, 128(1), 015704. https://doi.org/10.1103/PhysRevLett.128.015704.
5) Yoo, T., Xia, X., Ren, F., Jacobs, A., Tadjer, M. J., Pearton, S., & Kim, H. (2022). Atomic-scale characterization of structural damage and recovery in Sn ion-implanted β-Ga2O3. Applied Physics Letters, 121(7), 072111. https://doi.org/10.1063/5.0099915.

Co-Author(s): Kairolla Sekerbayev (Nazarbayev University), Alexander Azarov (University of Oslo), Zhandos Utegulov (Nazarbayev University), Andrej Kuznetsov (University of Oslo)

Azat Abdullaev

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