Visible and near infrared emitting thin film electroluminescent gallium nitride doped with rare earths

Visible and near-infrared (NIR) light-emitting thin-film electroluminescent gallium nitride (GaN) doped with rare earth (RE) elements was studied. The rare-earth-doped GaN thin films were prepared by radio frequency (RF) planar magnetron co-sputtering of separate targets consisting of a GaN compound target and a metallic rare earth target in a pure nitrogen atmosphere.; The luminescence of rare-earth-doped GaN was shown to be a strong function of its structure and properties, and growth parameters affected the structure and properties of the GaN host films. A phase transition from the thermodynamically stable wurtzite to the metastable zinc-blende structure at room temperature in GaN host films was observed upon increasing the impact energy of the bombarding species, thereby increasing the compressive stress in the GaN film. The switch from wurtzite to zinc-blende GaN occurred at a compressive internal stress of ∼1 GPa. The internal compressive stress above this threshold value apparently stabilizes the zinc-blende GaN phase at room temperature. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) showed that the impact by hyperthermal species yielded a highly condensed fibrous GaN microstructure with a smooth surface morphology due to annihilation of porosity by knock-on and bombardment-induced adatom mobility.; X-ray diffraction and texture analyses showed that the GaN films deposited at a low pressure had a predominant cubic phase with a preferred crystallographic orientation of the [111] direction perpendicular to the surface of the film. X-ray rocking curve data revealed that cubic GaN films grown with a lower growth rate exhibited a more highly [111]-textured structure.; Alternating-current thin-film electroluminescent (ACTFEL) devices were fabricated based on GaN doped with rare earth (RE) elements. Visible electroluminescent light emission peaks at 475 (blue), 530 (green), and 614 nm (red) were demonstrated at room temperature from GaN doped with thulium (Tm), erbium (Er), and europium (Eu), respectively. The near-infrared electroluminescent light emissions at 800, 1082, and 1550 nm were obtained at room temperature from GaN doped with Tm, neodymium (Nd), and Er, respectively. The emitted power densities of the fabricated ACTFEL devices were ∼1.53, 0.71, and 3.48 μW/cm2 for the GaN doped with ∼1 at.% of Er, ∼1.5 at.% of Tm, and ∼1.2 at.% of Nd, respectively. The dominant electroluminescence excitation mechanism for RE-doped GaN was found to be direct impact-excitation of the trivalent RE ions by hot electrons.