Research On Silicon Nanocrystal Rich Thin Films

In this thesis, we report the study on the structure and photoluminescence property of silicon nanocrystal rich thin films, which is considered as promising optoelectronic materials in silicon monolithic micro photonic integration. Based on this research, we extended our scope to nickel induced phase separation and nanocrystal growth in SiO_x films, and report the experimental and mechanism study of this phenomenon.Silicon nanocrystal rich SiO₂ (SRSO) films were fabricated by reactive sputtering and high temperature annealing. By controlling the fabrication technique, annealing temperature and annealing ambient, the structure and photoluminescence properties of the SRSO films were systematically studied. It is evidenced that the defects of Si-O bonding, quantum confinement efficiency and nanocrystal interface states are three major structural factors to influence the photoluminescence property of the SRSO film. Oxygen is observed to enhance the photoluminescence intensity of the film during post-annealing, and is considered to be a stable passivating atmosphere for SRSO films at a high temperature of 900oC instead of H₂.In order to further study the correlation between the silicon nanocrystal interface states and its photoluminescence property. We synthesized silicon nanocrystal rich Al₂O₃ (SRAO) films by sputtering and high temperature annealing. With a 2.42eV laser pumping at room temperature, two PL bands located at 1.53eV and 1.68eV respectively were observed from the SRAO sample annealed in N₂. Moreover, the correlative positions and intensities of these two PL bands were altered by post-annealing the sample in O₂. By qualitative analyzing, we consider the 1.68eV PL band origins from the Si=O bonds at the silicon nanocrystal interface, and the 1.53eV PL band is possibly due to the oxygen less defects in the film or a coupling effect between electronic and vibrational emissions.Based on the research of SRSO films, we introduced a 10nm thick Nilayer between the SiO_x film and the silicon substrate. Using equilibrium annealing and rapid thermal annealing, we studied the phenomenon and mechanism of nickel induced phase separation and nanocrystal growth in SiO_x films. It is found that comparing with the sample without Ni, the density of silicon nanocrystals is higher and the room temperature PL intensity of the SRSO film is stronger with the incorporation of the Ni interlayer, after annealing the samples at 1000 o C or higher. We also applied the 3d Avrami-Erofe've equation and the classical nucleation theory, which are kinetic and thermodynamic approaches respectively, to quantitatively analyze the experimental results. We concluded that the mechanism of NiSi2 induced nucleation is the origin of this phenomenon.