Luminescent properties and structural characteristics of sputter-deposited ZnGa2O4:Mn phosphor thin films

Abstract

The correlation between the luminescent properties and structural characteristics of ZnGa2O4:Mn phosphor thin films has been investigated. The ZnGa2O4:Mn films have been prepared by radio frequency planar magnetron sputter deposition from a 2 mol. % Mn-doped ZnGa2O4 target in an Ar-O2 gas mixture whose pressure ranged between 2 and 20 mTorr. Films deposited at gas pressures above 10 mTorr showed a random crystallographic orientation, while the films deposited ≤10 mTorr exhibited a preferential orientation of the [110] direction perpendicular to the film surface. Internal stress in the ZnGa2O4:Mn films became increasingly compressive upon decreasing the gas pressure, reaching a value of ∼1.7 × 1010 dyne/cm2 at 2 mTorr. The observed change in internal stress correlated with the changes in the crystalline structure of the films. After a post-deposition anneal at 800 °C, the crystallinity of the films was improved. The rms surface roughness of the annealed ZnGa2O4:Mn films did not systematically depend on the gas pressure. Both photoluminescence (PL) and cathodoluminescence (CL) resulted in green light, and the emission peaked at ∼505 nm. This was attributed to the Mn2+ 3d-3d intrashell 4T1 → 6A1 transition. The intensities of both PL and CL emission increased as the gas pressure decreased, presumably due to the better crystalline quality with a highly [110]-textured structure and a more densely-packed microstructure in the ZnGa2O4:Mn films deposited at lower pressures.