單一氮化物奈米線的電性傳輸特性; Electrical Transport Properties of Single III-Nitride Nanowire

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题名:	單一氮化物奈米線的電性傳輸特性;Electrical Transport Properties of Single III-Nitride Nanowire
作者:	張志仰;Chih-Yang Chang
贡献者:	物理研究所
关键词:	奈米線;電性傳輸;氮化鎵;氮化銦;GaN;nanowire;electrical transport;ZnO;InN
日期:	2006-06-16
上传时间:	2009-09-22 10:55:24 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文主要在研究單一氮化鎵 (GaN)及氮化銦 (InN)之奈米線電性傳輸特性。首先，將單一GaN奈米線元件以700~800oC熱處理之後，因為奈米線的表面對體積比很大，所以，表面的清潔處理將會大大影響所量測到電性的結果。我們利用紫外線臭氧清洗機(UV/Ozone)來輔助研究n型GaN奈米線表面的清潔。利用歐傑電子能譜(Auger electron spectroscopy)來量測一系列1-30分鐘不同的GaN 表面清潔的樣品，並發現此方法可以大大降低GaN表面的碳及氧的含量，但是，過度的長時間使用UV/Ozone處理將會有氧化物在奈米線的表面形成，使清潔目的得到反效果。將單一GaN奈米線元件熱處理及表面清潔之後，可製作不同奈米線長度的電元件，從奈米線的總電阻中減去兩端歐姆接觸電阻，可得知奈米線電阻率從71 Ω cm大大地降到0.7 Ω cm，電性特性的改善足足有兩個數量級之好。第二部分將介紹一種簡單地、低成本地單一根奈米線場效電晶體元件的製作方法，此元件基板為鍍上300 nm的氮化矽絕緣層的矽基板，此奈米線場效電晶體在700 oC 氮氣下熱處理之後，呈現n型的導電特質，載子濃度約2x1017 cm-3 ，飄移率約30 cm2/V s。更進一步地，從變溫電阻的結果曲線來看符合微擾穿隧效應將主導此元件的在接觸電極與半導體奈米線之間的傳輸。第三部分為介紹量測InN 奈米線電性特性，此InN奈米線亦由金催化劑利用熱化學氣相沉積法所核成，為了匹配功函數(work function) ，使用的四層接觸金屬分別為釟/鈦/鉑/金(Pd/Ti/Pt/Au) 這四種歐姆接觸金屬(ohmic contact metal)，我們使用傳輸線理論模型(transmission line method; TLM) 去求得奈米線與接觸金屬的特殊接觸電阻率(specific contact resistivity)為1.09 x 10-7 Ω cm2，接著可計算出直徑大於100 nm的InN奈米線本質電阻率為4x10-4 Ω cm，然而，直徑小於100 nm的InN奈米線在TLM模型下總電阻對長度/奈米線半徑的平方做圖呈現出反常非線性高斯遞減行為，違反歐姆定律，猜測是由於小尺度效應的影響所造成，若把電阻的貢獻看成是由每個散射中心所造成，使得電阻率與長度和截面積呈現正相關。接著量測電阻隨溫度的變化所得到一個正相關溫度係數，這告訴我們InN奈米線呈現出金屬的特性。 In this dissertation, the electrical transport properties studies on single GaN and InN nanowires were studied. First, we report studies on the effect of UV/ozone cleaning on n-type GaN nanowires. The UV/ozone cleaning for periods of 1-5 min reduced surface carbon and oxygen contamination, as determined by Auger electron spectroscopy measurements and led to a specific contact resistivity of 1.8x 10-2 Ω cm2 after annealing in the range 700-800 oC. After subtraction of this contact resistivity from the total resistance of the nanowire, it was found that the ozone treatment reduced the apparent resistivity from 71 to 0.7 Ω cm. Second, a simple fabrication process for single GaN nanowire field effect transistor on Si substrate was demonstrated. The as-grown GaN nanowires exhibited n-type conductivity (n~2x1017 cm-3, mobility of 30 cm2/Vs) after annealing at 700 oC. From the temperature-dependence resistance behavior, the transport was dominated by tunneling in these annealed nanowires. Third, the transport properties of single InN nanowires grown by thermal catalytic chemical vapor deposition were measured as a function of both length/square of radius ratio and temperature. The resistivity of the n-type InN nanowires with diameter>100 nm was measure by the transmission line method and the value was on the order of 4x10-4 Ω cm and specific contact resistivity for unalloyed Pd/Ti/Pt/Au ohmic contacts was near 1.09x10-7 Ω cm2. For InN nanowires with diameter <100nm, the total resistance did not increase linearly with length/square of radius ratio but decreased exponentially, presumably due to more pronounced surface effect. The usual Ohm’s law will fail in small nanowires in the diffusive regime when the wire radius is comparable with electron de Broglie’s wavelength or the scatter potential range. The temperature dependence of resistance showed a positive temperature coefficient and a functional form characteristic of metallic conduction in the InN nanowires.
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