Epitaxial growth and characterization of magnesium gallate (MgGa2O4) thin films by pulsed laser deposition

• Published in: Journal of alloys and compounds Vol. 972
• Main Authors: Hamid, Md Abdul, Samuels, Brian, Karmakar, Subrata, Halim, Md Abdul, Emu, Injamamul Hoque, Sarkar, Pallab Kumar, Taufique, M. F. N., Haque, Ariful, Droopad, Ravi
• Format: Journal Article
• Language: English
• Published: United States Elsevier 08-11-2023
• Subjects: Chemical state; Crystallinity; Epitaxial growth; Magnesium gallate; MATERIALS SCIENCE; Pulsed laser deposition; Surface morphology
• ISSN: 0925-8388

To advance high power device application of MgGa2O4, it is imperative to achieve crystalline epitaxial thin films and to observe its materials’ characteristics within a wide range of growth conditions. However, there is no published work on the growth of this promising ultrawide bandgap material till this day. In this study, we report the crystalline growth of MgGa2O4 thin films on c-plane (006) sapphire substrates using the pulsed laser deposition (PLD) technique in a broad range of temperature and oxygen pressure. The temperature range for this crystalline growth was within the temperature range of 300°C to 700°C and a pressure range of 1x10-1 to 1x10-3 Torr. Within this parameter range, the structural, chemical, optical, and surface property of MgGa2O4 thin films have been investigated. Specifically, the acquired XRD patterns confirmed the film growth along the [111] preferential crystal orientation in the lattice. Here, the rocking curve measurement of the prominent (222) plane showed an increasing trend of the crystallinity with growth temperature and pressure. Furthermore, the XRD phi (φ) scan demonstrated the six-fold rotational symmetry of the MgGa2O4 films and the epitaxial relationship of 30° between the film and the sapphire substrate. The XPS spectra confirmed the presence of +2 and +3 oxidation state for Mg and Ga respectively, in the films. The direct bandgap of MgGa2O4 films was obtained ~5.27±0.03 eV by analyzing the UV-Vis absorbance spectra using the Tauc equation. The SEM images exhibited a granular surface morphology of the MgGa2O4 films with an increasing trend in the grain size from low to high temperature and pressure. The refractive index and thickness of these films were in the range of ~1.90±0.02 and ~70±2.0 nm, respectively determined by fitting the spectroscopic ellipsometry data.