【Domestic Papers】Shandong University---Edge-Dependent Step-Flow Growth Mechanism in β-Ga₂O₃ (100) Facet at the Atomic Level

      Researchers from the Shandong University have published a dissertation titled "Edge-Dependent Step-Flow Growth Mechanism in β-Ga₂O₃ (100) Facet at the Atomic Level" in The Journal of Physical Chemistry Letters

Project Support

      This work was supported by the National Natural Science Foundation of China (Grants 5193000206, U24A20312, 62374079, and 62304097), National Key Research and Development Plan (Grants 2024YFA1208802 and 2023YFB4606900), Guangdong Basic and Applied Basic Research Foundation (Grants 2023A1515012048 and 2024A1515030224), and Shenzhen Fundamental Research Program (Grants JCYJ20230807093609019, JCYJ20220530114615035, JCYJ20240807170626004, and 2023112115707001). The computational resources are provided by the Center for Computational Science and Engineering at the Southern University of Science and Technology.

Background

      Gallium oxide (Ga₂O₃) has garnered enormous interest from the (opto-)electronics community as a promising next-generation ultrawide bandgap semiconductor. Among its polymorphs, the monoclinic β-Ga₂O₃, the most stable phase under ambient conditions, exhibits several remarkable properties, including an ultrawide bandgap (E_g ≃ 4.9 eV), a high breakdown electric field (E_crit ≃ 8 MV/cm), exceptional chemical and thermal stability (melting point ≃ 1720 °C), a large Baliga’s figure of merit (BFOM = 3444), a short ultraviolet cutoff edge of ∼ 260 nm, and high radiation resistance. Owing to these outstanding material properties, β-Ga₂O₃ possesses great prospects for applications in high-power electronics, solar-blind ultraviolet optoelectronics, and two-dimensional devices. To fabricate a high-performance β-Ga₂O₃-based device, a high-quality epitaxial thin film with a smooth surface and low defect density is essential. Particularly, homoepitaxy is significant for minimizing defect density in the β-Ga₂O₃ epitaxial thin film by avoiding lattice mismatch in heteroepitaxy. Recently, the homoepitaxy of β-Ga₂O₃ has been explored using several thin film growth techniques, such as metal−organic vapor phase epitaxy (MOVPE) (also referred to as metal−organic chemical vapor deposition, MOCVD, in the literature, molecular beam epitaxy (MBE), halide vapor phase epitaxy (HVPE), and mist chemical vapor deposition (mist-CVD).

Abstract

      Homoepitaxial step-flow growth of high-quality β-Ga₂O₃ thin films is essential for the advancement of high-performance Ga₂O₃-based devices. In this work, the step-flow growth mechanism of the β-Ga₂O₃ (100) facet is explored by machine-learning molecular dynamics simulations and density functional theory calculations. Our results reveal that Ga adatoms and Ga–O adatom pairs, with their high mobility, are the primary atomic species responsible for efficient surface migration on the (100) facet. The asymmetric monoclinic structure of β-Ga₂O₃ induces a distinct two-stage Ehrlich–Schwoebel barrier for Ga adatoms at the [00−1] step edge, contributing to the suppression of double-step and hillock formation. Furthermore, a miscut toward [00−1] does not induce the nucleation of stable twin boundaries, whereas a miscut toward [001] leads to the spontaneous formation of twin boundaries. This research provides meaningful insights not only for high-quality β-Ga₂O₃ homoepitaxy but also the step-flow growth mechanism of other similar systems.