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ZnS thin films with embedded in the Ge Si_3N_4 Nanocrystals and characteristics of

Author: QuanNaiCheng
Tutor: GaoZuo
School: Shaanxi Normal University
Course: Optical Engineering
Keywords: Thermal evaporation ZnS thin film Optical band gap Ge nanocrystals Photolummescence
CLC: TB383.2
Type: Master's thesis
Year: 2010
Downloads: 39
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Abstract


ZnS is a kind ofⅡ-Ⅵcompound semiconductors with a RT optical band gap of 3.7 eV and a high degree of transparency, which is considered as the material with potential applications in the areas such as solar cell, optical coating materials, laser diodes, electroluminescent devices and electrol-optical detector. Ge nanocrystals embedded in dielectric material (Si3N4, SiO2) have a very import potential application in the areas of photovoltaic, optoelectronic devices, high-capacity memory and light-emitting device.In this thesis, we prepared ZnS thin films with thermal evaporation method and studied the impact of substrate temperature and annealing temperature on the structure, composition, morphology and optical band gap of ZnS film. Using RF magnetron sputtering and annealing method prepared Ge nanocrystals, which embedded in Si3N4 film. Photoluminescence in the visible and near-infrared domain can be observed in the samples. We have studied the origin and influence of the annealing time on the evolution of photoluminescence, in correlation with the structural characterization performed by grazing-angle X-ray diffraction and Raman spectrometry. We obtained the following conclusions:1. The structure of ZnS thin film prepared by thermal evaporation process was cubiczinc-blende. The average grain size is increasing with a high substrate temperature and annealing. The preferred orientation is ZnS(111).2. Dislocation density in the ZnS thin films showed a reduction then growing trend with the increasing substrate temperature and annealing temperature.3. Substrate temperature and annealing temperature have an import influence on the compostition of our samples. When substrate temperature increased from 100℃to 400℃, atom percentage of the sample:[S]/[Zn], decreased from 1.32 to 0.85. When annealing temperature increased from 200℃to 600℃, the atom percentage decreased from 1.04 to 0.72. It’s very close to the stoichiometric at the substrate temperature of 300℃and the annealing temperature of 400℃.4. Quantum Size Effect and Burstin-Moss Effect was observed when the substract temperature and the annealing temperature increase. 5. According to the application of ZnS thin films used in CIS solar cells,considered both the changes in structure and optical band gap, and the best parameters of thermal evaporation and annealing process are substrate temperature of 300℃and annealing temperature of 400℃.6. Ge crystallinity and nanocrystal size was found to increase with the rise of annealing time. the sample is fully crystallized, after annealing at 800℃for 5min or longer.7. The observed PL band centered at 780nm is attributed to the T’∏→S0 optical transitions in GeO color centers, while the band centered at 540nm is the sum of peaks from Ge NCs,defect states in Ge/Si3N4 interface and silicon nitride.

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