介穩態奈米結晶矽鍺薄膜之物性研究與應用;The Physic Properties and Applications of Metastable SiGe Nano Crystalline Thin Films

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Title:	介穩態奈米結晶矽鍺薄膜之物性研究與應用;The Physic Properties and Applications of Metastable SiGe Nano Crystalline Thin Films
Authors:	歐陽曜聰;Ouyang,Yao-tsung
Contributors:	化學工程與材料工程學系
Keywords:	矽鍺;介穩態;快速熱退火;SiGe;metastable;RTA
Date:	2015-08-19
Issue Date:	2015-09-23 10:53:09 (UTC+8)
Publisher:	國立中央大學
Abstract:	本篇論文探討以簡易的共濺鍍方法鍍製非晶矽鍺薄膜於熱氧化矽之矽基板上，使用快速熱處理方式生成奈米結晶結構。矽鍺為完全固溶體，因為快速熱處理以致未達熱力學平衡，本篇主要成果為生成偏析鍺奈米結晶於非晶矽鍺薄膜中。實驗中利用同步輻射X光繞射、拉曼光譜儀鑑定矽鍺薄膜之微結構，再以高解析電子顯微鏡證實偏析鍺結晶存在，發現矽鍺薄膜中鍺結晶大小隨著鍺含量提高愈趨變大，以量化方式估算薄膜中的鍺結晶數量密度。鍺材料本身具備高吸收係數與高導電度之特性，實驗中以霍爾量測(Hall)與Tauc法說明其薄膜之電性與光學性質，薄膜具備低能隙(bandgap)與高遷移率(mobility)之優越特性，本論文藉由控制鍺結晶粒大小使其調控光學能隙。將偏析鍺結晶之矽鍺薄膜應用於光二極體，本實驗利用硼顆粒與磷擴散片摻雜矽鍺薄膜使成為p-n二極體，利用I-V分析探討其電性變化，研究成果於磷熱擴散30分鐘之後呈現整流特性；在照光影響下，正向偏壓之電流隨著鍺含量提升而增加，並以異質量子概念解釋奈米晶與非晶界面對其電性影響。另外，本論文提出漸進式能隙之概念嘗試堆疊不同含量之矽鍺薄膜，發展出吸收不同波段之光波長之方法，驗證出漸進式之結構二極體於照光下電流大幅增加，未來漸進式吸收預期將可與光感應器或太陽能電池作為結合。本論文之結果得知，非穩態之偏析鍺結晶可有效提高遷移率並利用鍺晶粒大小控制光學能隙，使用此特性製備出漸進式結構之光二極體，增加吸收光譜範圍，亦提供業界於元件設計上之參考。 ;Amorphous Si1-xGex films were prepared by co-sputtering on an oxidized Si wafer, followed by rapid thermal annealing, which formed nanocrystal films; since the Ge nanocrystals were not formed at thermodynamic equilibrium, an amorphous Si1-xGex matrix was finally obtained. Synchrotron radiation X-ray diffraction and Raman spectroscopy were utilized to identify the microstructure of the Si1-xGex films. High-resolution transmission electron microscopy was used to characterize the increase in size of the grains in the Ge nanocrystals with the Ge content. The electrical and optical properties were determined by Hall measurement and using Tauc’s method. Ge segregation permitted high mobility of the carriers and enhanced the electrical properties of the films. The low optical bandgap of the films made them good light absorbing materials. The results herein suggest that the grain sizes of the films can be used to tune their bandgaps. P-n junction diode with good rectifying characteristics has been prepared based on the segregation of Ge crystals of Si1-xGex thin films deposited by co-sputter system. The current-voltage characteristics in darkness and under illumination were studied. The correlation between the p-n junction performance and the microstructure of the films is discussed. The rectifying property became stronger as the fraction of Ge in the Si1-xGex films increased. The heteroquantum model was demonstrated in relation to the diodes and the energy band diagram. The optical bandgap can be tuned by controlling the grain size in Ge and SiGe crystals. The graded structure of the Si1-xGex photodiode is proposed to widen the light absorption region. The concept can be used to design high-efficiency photodiodes.
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