Thermal Conductivity of β-Phase Ga2O3and (Al x Ga1-x )2O3Heteroepitaxial Thin Films

Yiwen Song, Praneeth Ranga, Yingying Zhang, Zixuan Feng, Hsien Lien Huang, Marco D. Santia, Stefan C. Badescu, C. Ulises Gonzalez-Valle, Carlos Perez, Kevin Ferri, Robert M. Lavelle, David W. Snyder, Brianna A. Klein, Julia Deitz, Albert G. Baca, Jon-Paul Maria, Bladimir Ramos Alvarado, Jinwoo Hwang, Hongping Zhao, Xiaojia WangSriram Krishnamoorthy, Brian M. Foley, Sukwon Choi

Research output: Contribution to journalArticlepeer-review

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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 (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 «112» 0»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 (2¯ 01)-oriented β-(AlxGa1-x)2O3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(AlxGa1-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-(AlxGa1-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 (AlxGa1-x)2O3 thin films and lays the groundwork for the thermal modeling and design of β-Ga2O3 electronic and optoelectronic devices.

Original languageEnglish (US)
Pages (from-to)38477-38490
Number of pages14
JournalACS Applied Materials and Interfaces
Volume13
Issue number32
DOIs
StatePublished - Aug 18 2021

All Science Journal Classification (ASJC) codes

  • Materials Science(all)

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