Blue emission of Cerium doped Aluminum (oxy)-nitride thin films prepared by reactive sputtering technique

Recently, blue light emitting solid-state materials received high attention for use in white LEDs and other luminescent applications. In this direction, phosphors- doped nitrides and oxy-nitrides composites attracted much... [ view full abstract ]

Recently, blue light emitting solid-state materials received high attention for use in white LEDs and other luminescent applications. In this direction, phosphors- doped nitrides and oxy-nitrides composites attracted much potential due to their thermal, chemical stability and the possibility to tune their electronic structure to adapt to the required applications. In particular, the III-nitrides (e.g. AlN, GaN) have been considered as a suitable host material for phosphors that emit in UV-visible range due to its large bandgap. Thus, the purpose of this study is to sensitize blue emission from rare earth doped AlN as a wide bandgap semiconductor.
In the present work, 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 <002> 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. 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.