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

Abstract

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 [21¯1¯0]Al2O3 and [101¯0]Al2O3 zone 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 the interface region to be (2¯01)β-Ga2O3∕∕(0001)Al2O3 and [102]β-Ga2O3∕∕[21¯1¯0]Al2O3 or [1¯02¯]β-Ga2O3∕∕[21¯1¯0]Al2O3 for the undoped film, and (111)γ-Ga2O3∕∕(0001)Al2O3 and [21¯1¯]γ-Ga2O3∕∕[21¯1¯0]Al2O3 or [2¯11]γ-Ga2O3∕∕[21¯1¯0]Al2O3 for the Mn-doped film. Mn ions are uniformly dissolved in the film with 7.8 cation % and no detectable precipitates are found. Mn-L2, 3 energy-loss near-edge structure reveals that Mn ions take the valency of 2+, which is consistent with Mn-L2, 3 near edge x-ray absorption results in our previous report.