Room-temperature photoluminescence and electroluminescence properties of sputter-grown gallium nitride doped with europium

Abstract

We have studied the room-temperature photoluminescence (PL) and electroluminescence (EL) properties of europium (Eu)-doped gallium nitride (GaN) thin films grown by radio frequency planar magnetron cosputter deposition. X-ray photoelectron core level spectra collected for Eu 4d revealed that the Eu ions in the GaN host were mainly in the trivalent state. A series of PL peaks were observed in the region of 530–700 nm, with the most intense peak at 614 nm. They were assigned to the radiative transitions between the 4f6 energy levels of the Eu3+ ion, specifically DJ5→7FJ′ (J=0,1;J′=1,2,3,4). The maximum PL intensity was obtained at a Eu concentration of ∼1.8 at. %. Electroluminescent devices were fabricated with an Al electrode, Eu-doped GaN light-emitting layer, Al2O3–TiO2 dielectric layer over an indium-tin-oxide electrode on a Corning 7059 glass substrate. The EL emission spectra from the fabricated devices were almost identical to the PL spectra. Higher electron energies (higher applied voltages) were needed to excite Eu3+ ground-state electrons into the higher-lying D15 state, which is consistent with the EL excitation mechanism being direct impact by hot electrons.