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Design and Fabrication of Si Nanocrystals Film on Glass Substrate

Author: XuBenChao
Tutor: LiuShiMin
School: Yanshan University
Course: Materials Science
Keywords: Si nanocrystals first principle quantum effects band structure and density ofstates Rapid Thermal Processing
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 24
Quote: 0
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Abstract


The film of Si nanocrystals has more obvious advantages. It is non-toxic, abundantraw materials, high efficiency and low cost. What’s more, it has the quantum effects. Thephotoelectric properties can be changed by controlling the size of Si nanocrystals. So ithas a very broad application prospects. It is one of highlights of recent scientific researchand industrial development. In this paper, we used the first-principles calculations methodwhich are based on density functional theory study. We analyzed and discussed thevariation law of the photoelectric properties of the different sizes Si nanocrystalsembedded SiO2. Finally, we tried to prepared the different sizes Si nanocrystals embeddedSiO2. The purpose is to seeking the suitable preparation process and realizing thecontrollable of different sizes of Si nanocrystals.After analyzing the optimized model, we can find that the size of Si nanocrystals issmaller, the constant and the volume of the film is lager. This is relative with the bonglength of Si-Si and Si-O. The optimized system was fully relaxed. So with the package ofSiO2, the composite film existed as a relatively stable metastable state. According to thecalculated electron density of states we can see the nonlinear optical phenomenon ismainly caused by the hybrid electronic transitions and falling caused which around theFermi level. The Si nanocrystals sizes are smaller, and then the optical band gap is greater.After comparising the optical performance of the different film, we can see the size of Sinanocrystals is smaller the corresponding absorption coefficient in is greater in theultraviolet range. And the absorption edges are occurred blue shift. But the absorptioncoefficient is very low at the visible and near-infrared part. And the reflectance andrefractive index is also stabled around some certain values. This is relative with the energyof the wavelength. Finally calculated the transmittance in the visible and near-infrared part,we found that the size of Si nanocrystals is smaller; the according transmission rate isgreater. the theoretical calculation of the transmittance is up to97%.Finally, we tentatively used the hot wire chemical vapor deposition（CVD） to preparethe film of Si nanocrystals embedded SiO2. After researching we can find that the heattreatment temperature is around9001000℃, the film has better performance. The heat treatment temperature is higher, the grain size is larger and the crystal is relativelycomplete. Then we researched the optical properties. We can see that the film has a highabsorption coefficient. The size of Si nanocrystals is smaller, the absorption coefficient ishigher and the transmittance is also higher. The law of the experiment is consistent withthe theoretical calculation. The transmittance of the actually prepared film is up to91.7%.

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