以濺鍍法成長ZnO-SiO2與ZnO-SiNx微晶玻璃薄膜之光學特性研究

Abstract

本實驗以濺鍍法將氧化鋅（ZnO）奈米顆粒鑲嵌於氮化矽（SiNx）透明基材中以製成ZnO-SiNx半導體微晶玻璃（Semiconductor-doped Glass，SDG，稱之為ZSN系統），並分析其光學性質、摻雜成分與微觀結構之關係；所得之結果並與先期完成之ZnO-SiO2半導體微晶玻璃（稱之為ZSO系統）之性質比較，以了解氧化鋅在不同介質中之光學性質。 電子顯微鏡〈Transmittance Electron Microscopy，TEM〉之微觀結構分析顯示，低摻雜時，圓形氧化鋅奈米顆粒均勻散佈在兩透明介質中，大小約5至10 nm；ZSN系統中，當貼靶面積高於22.68 at.%，薄膜內氧化鋅含量過大而形成連續柱狀結構，已非圓形之奈米顆粒。電子能譜儀〈Electron Spectroscopy for Chemical Analysis，ESCA〉分析結果顯示鋅原子以Zn2+存在於薄膜內，氧原子則以氧化鋅晶格內之O2□、非晶介質中之O2□、以及非完全鍵結或吸附氧狀態存在。在光學性質部分，ZSN與ZSO系統皆能產生黃-綠光、藍光與紫外光發射光譜。在ZSO系統中，黃綠光機制主要與氧空缺有關；以奈米尺度鑲於基材的氧化鋅產生諸多氧化鋅/二氧化矽界面，導致電子空乏區寬度增加，因此導帶電子躍遷至鋅空缺的機會（ ）大增，因而產生藍光發射。黃-綠發光與藍光強度隨摻雜量增加黃-綠光強度增強、藍光強度減弱。在ZSN系統之發黃綠光機制與ZSO相同，藍光則因氮之摻雜產生受子能階，當導帶電子躍遷至受子能階時即產生藍光發射或因施子密度增加而增加了電子空乏區的寬度，故增加激態電子躍遷至鋅空缺的機率，而產生藍光；但ZSN系統的貼靶面積越大，藍光強度增強、綠光強度減弱，與ZSO系統相反。

The target-attachment sputtering method was adopted to prepare the ZnO-SiNx semiconductor-doped glass (SDG) samples (called ZSN system) and their luminescence properties, composition and microstructures were characterized. The experimental results of ZSN system were compared with those of ZnO-SiO2 SDG samples (called ZSO system) obtained previously so that the luminance properties of nano-sized ZnO particles embedded in different matrixes can be understood. As revealed by TEM analysis, spherical ZnO nanoparticles about 5 ~ 10 nm in diameter uniformly dispersed in both matrices when doping concentrations were low. In ZSN system, the ZnO microstructure changed from discrete particles to typical column-like phase when the chip-to-target area ratio exceeded 22.68%. The ESCA analysis indicated that in ZnO lattice the charge status of Zn is Zn2+, and as to O element, it becomes O2□ in ZnO lattice and in amorphous matrixes or incompletely bonded or absorbed O. In the part of luminance properties, three emission bands, the yellow-green, blue and UV (ultra-violet) emissions were observed in the ZSO and ZSN samples. In ZSO system, the oxygen vacancies were the emission centre of yellow-green luminescence; the presence of the blue emission was attributed to the large number of ZnO/SiO2 interfaces which enlarges the depletion layer width and then amplifies the transition from conduction band (CB) to the zinc vacancies ( ) level. In ZSO system, the intensity of green/yellow emission increased with the ZnO content, while the intensity of blue emission behaved oppositely. The mechanism of green/yellow emission in ZSN system was the same as that of ZSO system. As to the blue emission in ZSN system, two possible mechanisms were deduced. One is the transition from CB to the impurity acceptor levels induced by the p-type nitrogen doping in ZnO. The other is related to the CB-to- transition due to the depletion layer enlargement resulted from the increase of acceptor density. The intensities of blue emissions in system ZSN could be modulated by ZnO content, however, it increased with the increase of ZnO doping concentration in contrast to ZSO system.