Spectroscopic and structural investigation of undoped and Er3+ doped hafnium silicate layers

This paper demonstrates the functionality of radio-frequency magnetron sputtering for the fabrication of undoped and Er-doped Si-rich-HfO2 films with specific structural and spectroscopic properties. The effect of post-deposition treatment on film properties was investigated by means of Fourier-transform infrared spectroscopy, Raman scattering and photoluminescence methods, as well as Transmission Electron microscopy. It was observed that annealing treatment at 850–1000 °C causes phase separation process and the formation of HfO2, SiO2 and pure Si phases. This process stimulates also an intense light emission in the 700–950-nm spectral range under broad band excitation. The phase separation mechanism as well as the nature of radiative transitions were discussed. Photoluminescence was ascribed to carrier recombination in silicon clusters and host defects. The appearance of silicon clusters was also confirmed by the comparison of luminescent properties of pure HfO2, SiO2, Si-rich-HfO2 and Si-rich-SiO2 films. Additional argument for Si clusters’ formation was obtained under investigation of Er-doped Si-rich HfO2 films. These latter demonstrated 1.54-µm Er3+ luminescence under non-resonant excitation originating from an energy transfer from Si clusters towards Er3+ ions.