鉍奈米線的製作與其傳導特性研究

Fabrication and transport property characterization of bismuth nanowires

謝依珊(Yi-Shan Sie)

指導教授 ： 林浩雄

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202204171

摘要

本論文於厚度< 20 nm之鉍薄膜上開發鉍奈米線製程，使用氦離子微影系統(Helium ion beam lithography, HIBL)以及反應式離子蝕刻方式製備，討論製程上不同參數使用以及影像的結果，曝光劑量主要由調整氦離子束移動間距(spacing)與停留時間(dwell time)所控制，由實驗得知對我們的鉍薄膜而言，使用劑量6.1~8.3 µC/cm2會是較為合適的參數，並且spacing設定為6與7nm。將一般黃光製程製備的Hall bar使用氦離子束微影系統將尺寸由100 µm分別微縮至線寬500 nm、200 nm與60 nm，接著使用霍爾量測系統(Hall measurement)進行樣品編號S0881(B)、S0869(B)的Hall bar變溫量測，變溫範圍為300 K~10 K，磁場範圍為-1 Tesla ~ 1 Tesla。
電性傳輸特性可以視為總電阻由表面態(surface state)電阻與主體能態(bulk state)電阻所貢獻，利用G(T)模型擬合將主體能態與表面態分離，發現樣品S0881(B)、S0869(B)在溫度300 K~10 K範圍內皆由表面態主導。接著，使用EMA模型進行擬合，會得到不同溫度下的等效遷移率以及等效載子濃度，由不同線寬的Hall bar量測，發現等效載子濃度與等效遷移率對溫度變化皆不大，表示表面態與溫度和尺寸較無影響。
G(T)模型也能經由擬合得到等效能隙值，我們進行了100 µm、500 nm、200 nm、60 nm四種線寬Hall bar等效能隙的分析與討論，線寬越小的奈米線實驗擬合的等效能隙越大，而再將實驗擬合的等效能隙與二維量子侷限效應理論計算相比，發現實驗幾乎低於理論值，我們認為會有此差異是由於樣品S0881(B)晶格的grain boundary會額外提供載子致使整體電阻下降，因此造成實驗值與理論值不相符。而當線寬尺寸增加至約大於grain size時，單位面積下的grain boundary數量則會相當，因此線寬100 µm與500 nm Hall bar實驗值擬合的等效能隙會相近。

關鍵字

鉍薄膜 ； 霍爾效應 ； 表面態 ； 氦離子束微影系統 ； 量子侷限效應

並列摘要

Developed a bismuth nanowire process on bismuth film with a thickness of < 20 nm, using helium ion beam lithography and reactive ion etching. We discuss different parameters in the process and the results. The exposure dose is controlled by adjusting the spacing and dwell time. For our bismuth film, the dose used is 6.1~ 8.3 µC/cm2, and the spacing is 6 and 7nm. The Hall bar was reduced from 100 µm to 500 nm, 200 nm and 60 nm, and then the Hall measurement was used to measure the samples. The temperature range was 300 K~10 K, and the magnetic field range was -1 Tesla~1 Tesla.
The electrical transport characteristics can be regarded as the total resistance contributed by the surface state and bulk state. Using G(T) model fitting to separate the bulk state and surface state,we found that S0881 (B) and S0869(B) are dominated by surface states from 300 K to 10 K. Then, using EMA model. By measuring the Hall bar, we found that the equivalent carrier concentration and equivalent mobility change with temperature. Indicating that the surface state has little effect on temperature and size.
The G(T) model fitting can obtain the effective band gap. We have discussed the effective band gap with four line widths. The smaller the line width is, the larger the effective band gap is, and then compared with the theoretical calculation of the quantum confinement effect, it is found that the experimental value is almost lower than the theoretical value. This difference is due to the grain boundary of the sample S0881(B) will provide additional carriers to reduce the overall resistance, so the experimental value doesn’t match the theoretical value. When the line width increases to larger than the grain size, the number of grain boundaries per unit area will be similar, so the effective band gaps fitted by the experimental values of line width 100 µm and 500 nm will be similar.

並列關鍵字

Bismuth thin film ； Hall effect ； surface state ； Helium ion beam lithography ； Quantum confinement effect

參考文獻

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