Microstructure of Mn-doped γ-Ga₂O₃ epitaxial film on sapphire (0001) with room temperature ferromagnetism

Mn-doped Ga₂O₃ thin film showing room temperature ferromagnetism has been grown on a sapphire (0001) plane by using a pulsed-laser deposition technique. The microstructure of the Mn-doped film is investigated in detail using selected-area electron diffraction, high-resolution transmission electron microscopy (HRTEM), x-ray energy-dispersive spectroscopy, and electron energy-loss spectroscopy, in comparison with an undoped film. Careful diffraction analysis with the [2110]_Al2O3 and [101̄0] _Al2O3zone axes of the substrates reveals that the Mn-doped film shows the γ-Ga₂O₃ phase with a defective spinel structure, while the undoped film shows the β-Ga₂O₃ phase. The orientation relationship between the film and substrate is determined by electron diffraction and HRTEM from themterface region to be (2̄01)_β-Ga2O3//(0001)_Al2O3 and [102] _β-Ga2O3//[2110]_Al2O3 or [1̄02̄] _β-Ga2O3//[2110]_Al2O3 for the undoped film, and (111)_γ-Ga2O3//(0001)_Al2O3 and [211] _γ-Ga2O3// [2110]_Al2O3 or [2̄11] _γ-Ga2O3//[2110]_Al2O3for the Mn-doped film. Mn ions are uniformly dissolved in the film with 7.8 cation % and no detectable precipitates are found. Mn-L_{2, 3} energy-loss near-edge structure reveals that Mn ions take the valency of 2+, which is consistent with Mn-L _{2, 3} near edge x-ray absorption results in our previous report.