Cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature (RT) using radio frequency (RF) reactive sputtering. As-grown samples were then subjected to rapid thermal annealing (RTA). X-ray diffraction and high resolution transmission electron microscopy (HRTEM) revealed a well crystalline textured microstructure with single [002] out-of-plane orientation in both as-grown and annealed samples. A strong RT blue emission from post-deposition annealed samples was detected when excited by 266 and 325 nm laser. Electron energy loss spectroscopy (EELS) at the Ce edges reveal the dominant oxidation state of Ce atoms, which undergoes a change from of Ce 4+ to Ce 3+ ions after RTA annealing in Ar atmosphere. The chemical composition was analyzed by Rutherford backscattering spectrometry (RBS) and contrasted to HRTEM images. Our findings indicate that the surface oxidation during the post-deposition annealing in Ar plays an important role in the PL response by changing the oxidation state of Ce ions from optically inactive ions (Ce 4+ ) to the optically active ones (Ce 3+ ). Moreover, the importance of this oxidation is further confirmed by the excitation mechanisms responsible for blue emission determined by PL excitation measurements.

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