Strong Room Temperature Blue Emission from Rapid Thermal Annealed Cerium-Doped Aluminum (Oxy)Nitride Thin Films

Abstract

Cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature (RT) using radio frequency (RF) reactive sputtering. As-deposited 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-deposited and annealed samples. Strong RT blue emission from post-annealed samples was detected under optical excitation either by 325 or 266 nm cw lasers. Electron energy loss spectroscopy (EELS) measurements at the Ce edges reveal the dominant oxidation state of Ce atoms, which undergoes a change from of Ce to Ce 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) to the optically active ones (Ce). Moreover, the importance of this oxidation is further confirmed by the excitation mechanisms responsible for the blue emission determined by PL excitation measurements.https://doi.org/10.1021/acsphotonics.7b00233