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  • 學位論文

合成摻氮超奈米晶鑽石薄膜做為紫外光感測器之應用

Fabrication of n-doped ultrananocrystalline diamond films for UV sensor applications

指導教授 : 林啟瑞
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摘要


鑽石具有寬能隙及許多優異的物理與化學複合特性,被科學界喻為下個世代的半導體材料,但是一般化學氣相沈積法所合成的微米晶鑽石膜(MCD films),其粗糙度過大且不易透過摻雜提高其半導體特性,是MCD膜無法導入光電元件與應用的最大問題,故合成晶粒尺寸為奈米/超奈米等級之鑽石膜(Nanocrystalline/Ultrananocrystalline diamond, NCD/UNCD),被視為最佳解決方法之一。因此,本研究以微波電漿束化學氣相沈積系統改變甲烷濃度合成超奈米晶鑽石膜(UNCD films),並且透過氮元素之摻雜形成含氮超奈米晶鑽石膜(UNCD:N films),提升UNCD膜之電性,並探討在氬氣電漿改變甲烷濃度、工作壓力及氮氣濃度的影響,亦討論其薄膜之結構、光學、電性及薄膜基本性質之影響,並將鑽石薄膜製備為紫外光感測器,且探討其紫外光感測器之特性與效能。 研究中發現在氬氣電漿下提升甲烷濃度將使MCD薄膜轉變成UNCD薄膜,合成出低表面粗糙度以及晶粒大小為超奈米級之鑽石薄膜。在摻氮後薄膜之微結構及電性均明顯受到氮元素摻雜之影響,其中,在1%微量氮摻雜下將有效誘導鑽石朝(100)結晶面及特定方向成長,並發現晶粒形成針狀(needle-like)結構。 利用不同鑽石薄膜製備出紫外光感測器於光電導之探討,發現UNCD:N薄膜具有明顯的電流值變化(2.89 orders),主因是摻氮後晶粒成針狀可增加比表面積之光吸收率、表面較為平滑可降低暗電流及摻氮後提升電性所導致,且具備有良好的時間響應以及穩定的再現性,可應用於紫外光感測器。

並列摘要


Diamonds are considered as an ultimate material due to their own large energy gap and unique physicochemistry characteristics. Microcrystalline diamond (MCD) films, synthesized by conventional chemical vapour deposition (CVD) processes, however, possess high surface roughness due to their facet morphology. Also, this process are not readily available for doping activities, and thus hindering the potential uses of MCD films in semiconductor engineering fields. One way of synthesizing nanocrystalline/ultrananocrystalline diamond (NCD/UNCD) films is well-regarded as the effective method for resolving those restrictions. In this study, we propose here a method to synthesize ultrananocrystalline diamond (UNCD) using a home-made microwave plasma jet chemical vapour deposition (MPJCVD). Aiming at improvement of the electrical properties, nitrogen doping were conducted during the synthesis process for UNCD:N films. The effects of methane concentration, working pressure, and nitrogen incorporation on characteristics of the UNCD and UNCD:N films were investigated. In addition, the ultraviolet (UV) detection performance of the as-synthesized UNCD:N films were studied. In the synthesis of UNCD films, it was shown that increase in CH4 concentration induced the nanonization of diamond grains from microcrsytalline to ultrananocrystalline structure. The diamond growth by MPJCVD system was found to have high plasma density and ensure high activity species at low microwave power, thus led to ultra-smooth surface and ultrananocrystalline diamond grains of the as-synthesized films. As incorporated with nitrogen during the UNCD synthesis process, significant changes in microstructure, surface roughness, electrical and optical properties were observed. The low nitrogen doping (1%) also resulted in preferred growth in (100) orientation of diamond grains and needle-like shape in morphology of the UNCD:N films. In other stage of this study, the as-synthesized UNCD:N films were employed as absorption layer for UV detection application. The effects of microstructure and nitrogen incorporation on UV detection performance were studied. The UNCD:N film with needle-shape morphology possessed excellent photoconductivity which photo-dark current ratio achieved 2.89 orders with highly fast, stable, and reproducibility response to UV irradiation in air ambient. These good performance of the fabricated detector were due to the increase in UV irradiation absorption as results of a high surface-to-volume ratio of the UNCD:N films. Also, the obtained highly smooth surface and nitrogen incorporation of the films indeed ensured a relatively low dark current as well as good electrical characteristics of the fabricated UV detector. The above results demonstrated a prosperous applications of UNCD:N films in UV detection devices in the future.

參考文獻


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