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Preparation of phase separation of the amorphous silicon oxide and nanocrystalline silicon mosaic silica

Author: GanJie
Tutor: WuJiaDa
School: Fudan University
Course: Optics
Keywords: Nanocrystalline silicon Photoluminescence Phase separation Crystallization Thermal annealing Pulsed laser deposition
CLC: TN304.1
Type: Master's thesis
Year: 2011
Downloads: 23
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Abstract

Despite enormous challenges, appeared in the field of photonics Si still have high hopes, various nanostructures Si material optical properties different from the bulk Si material luminescence properties, stirred up the people to the light-emitting Si and Si based optoelectronic devices of great interest. Among them, the nanocrystalline Si mosaic silica (Si-NCs/SiO2), is one of the near future the most promising breakthrough in the field of photonics, light-emitting Si material. THIS Master Thesis Si-NCs/SiO2 of material as the research object, the deposition and annealing treatment the Si-NCs/SiO2 method for preparing an amorphous silicon oxide (a-SiOx), a-SiOx Si-NCs/SiO2 The transformation process research, by a-SiOx and after annealing of the sample, including changes in the characterization analysis Si-NCs/SiO2 structure and characteristics of investigation and study, focusing on a-SiOx phase separation and satisfied crystal Si is formed on the process and mechanism. The high purity Si target material is deposited amorphous SiOx O content of approximately 1.2 x 02 with an atmosphere of low pressure pulsed laser deposition method, and its refractive index of about 1.7 in the near infrared band, the extinction coefficient close to 0 (~ 10-4), in the visible to near-infrared transmittance of more than 80%, was a strong absorption in the ultraviolet absorption coefficient increases rapidly with decreasing wavelength, only a weak defect under UV excitation light. After 60 min of annealing temperature of 1100 ℃ in N2, a-SiOx into Si-NCs/SiO2 nanocrystalline Si average radius of 4.5 nm, due to the surplus Si precipitates matrix become chemical composition ratio of SiO2, Si -NCs/SiO2 the refractive index decreases to 1.65 extinction coefficient increases an order of magnitude, transmittance and the absorption coefficient is substantially constant. The thus prepared Si-NCs/SiO2 good luminescent properties, with the the nanocrystalline Si light-emitting characteristics of the fluorescence emission in the ultraviolet excitation. It was also found deposited in 0.7 Pa pressure O content of 1.2 a-SiOx best luminescent properties after annealing. Detailed study visits annealing temperature and annealing time on the structure and characteristics of the sample annealed a-SiOx to the transition of Si-NCs/SiO2 found this is not a simple commonly referred to as phase separation process, and It is precipitated and the precipitated crystalline Si and Be margin Si, a-SiOx Si nano was embedded in the remaining Si02 matrix, and the conditions and the rate of occurrence of these two processes occurs a great difference. Fourier transform infrared spectroscopy shows that the surplus Si, a-SiOx from about 500 ° C begins to precipitate the Si precipitates extent gradually increase as the temperature rises, the temperature was raised to 1000 ° C enables the process substantially complete precipitation of Si. Raman scattering spectroscopy showed that the crystallization temperature of precipitated Si is much higher, up to 1000 ℃, only a small part of the Si crystal, about 1100 ° C allows the precipitated Si effective crystallization Be nanocrystalline Si, while the temperature is too high, easy to make si growth precipitated to a large grain, resulting in the average grain size is too large; analysis results also showed that, even in the most suitable temperature, precipitated Si crystallization rate is far less than the rate of precipitation of the surplus Si, annealing about 10min A-SiOx shift the concentration having a nanocrystalline si Si-NCs/SiO2, continues this process until 120 min, the precipitated prior to crystallization using amorphous Si Si clusters, have a certain amount of Si crystals, form of existence. Of the a-SiOx transition to Si-NCs/SiO2 process and mechanism can be explained by the sample photoluminescence properties with annealing conditions change. After 1000 ° C annealed samples began firing with the the nanocrystalline Si light-emitting characteristics of the fluorescence, fluorescence intensity is enhanced as the annealing temperature increases, the strongest sample fluorescence after 1100 ° C annealing, continue to improve the annealing temperature increases due to the average grain size light-emitting nanocrystalline Si concentration decreases the fluorescence intensity. Further, in the 1100 ° C temperature, the longer annealing time may be effectively enhanced photoluminescence intensity of Si-NCs/SiO2 improve Si-NCs/SiO2 luminescent properties.

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