The essential role of oxygen in activation the blue emitting light from cerium doped Aluminum nitride thin films

Abstract

Oral presentation given at the 2017 E-MRS Spring Meeting, held in Strasbourg (France) on May 22-26, 2017.Rare earth-doped III-nitrides such as GaN and AlN, attract great attention in lightening and optoelectronic applications. Particularly, AlN with large optical bandgap (6.2 eV) can offer an opportunity to cover wide range of light spectrum from UV to IR regions. In addition, AlN with high thermal conductivity (300 W/mK) is a very suitable material for high power working optoelectronic devices. Exploiting the large bandgap and the thermal conductivity features of AlN lead to open the door for generating blue emission with low thermal quenching effect even at high power operation. These are very interesting prerequisites for establishing stable white light emitting diodes (w-LED). Seeking for realization the blue emission from AlN, cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature using radio frequency (RF) reactive sputtering. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) revealed a well crystalline textured microstructure with single out-of-plane orientation. Strong blue emission from the prepared samples was detected when excited by 325 nm laser. Electron energy loss spectroscopy (EELS) has been used to reveal the dominant oxidation state of Ce atoms, which undergoes a change from of Ce(IV) to Ce(III) ions after annealing. The chemical composition was analyzed by simulation of Rutherford backscattering spectrometry (RBS) and compared to HRTEM images. A clear correlation between microstructure, composition and sample photoluminescence (PL) was established. It was found that surface oxidation during post-deposition annealing plays an important role in the PL response of the samples. The role of oxygen in the excitation mechanism was explained from the photoluminescence excitation measurements. We believe that the strong blue emission in this new (oxy)-nitride material holds great potentials for solid state lighting applications due to its thermal and chemical stability as well as the luminescence efficiency. Moreover, the comprehensive approach conducted within this study could serve as a guideline for better understanding and the design of the luminescence behavior in rare earth-doped (oxy)-nitride thin films