探索氧化鋅奈米線元件在不同電極尺度下的電性傳輸

Abstract

隨著元件尺度的縮小，介面所產生的接點電阻會逐漸主導元件的電性，本篇論文我們將探討當尺度更進一步縮小至奈米級時，蕭特基接觸有何改變，並與本質氧化鋅的傳輸做比較。 在本次實驗中我們設計兩種類型的元件來探討不同類型的傳輸模式，兩種元件皆使用直徑約為70 nm的氧化鋅奈米線，經過450~550 ℃高溫退火24小時以增加其氧缺陷並提高導電率。第一種類型是直接將氧化鋅奈米線在矽基板上製成兩點量測之元件，並將此種元件稱為氧化鋅奈米元件，而第二種類型則是利用金奈米線作為電極去交疊氧化鋅奈米線，並在兩奈米線上外加電極製成元件，稱為金奈米線電極元件，此種元件的接觸面積可以縮減至約五千平方奈米的數量級，以達到我們想觀察小接面的電性傳輸行為的目的。兩種元件可分別探討氧化鋅奈米線的本質傳輸情形與奈米尺寸接點電阻之情形，量測各溫度的電流-電壓曲線，對兩者進行分析。 氧化鋅奈米線元件的傳輸行為，可以使用熱活化傳輸理論與變程跳躍傳輸理論電導並聯的模型來擬合，在高溫時由熱活化傳輸主導，低溫時由三維變程跳躍傳輸主導，若活化能越低則要在越低溫的狀態下才能觀察到三維變程跳躍主導的情形。 金奈米線電極元件，為一由蕭特基接面主導的之元件，可由各溫度的電流-電壓曲線以熱離子發射理論以及蕭特基效應擬合，進而觀測到其位障大小以及位障隨電壓增大而減小的蕭特基效應，所得到之位障約為20 meV再將所得到之位障大小對電壓作圖，再根據熱離子發射理論，可使用蒙地卡羅法求出其理想位障高度以及摻雜濃度。

The electron transport in ZnO nanowires and the nanoscale metal/semiconductor interface are studied from analyses of temperature-dependent current-voltage behaviors in the temperature range from 30 to 300 K. In this study, 70 nm-diameter ZnO nanowires were used for device fabrication. By using electron-beam lithography, we fabricated one kind of devices having two Ohmic-contact electrodes on ZnO nanowires to study electron transport. We found that the integrated models of thermal activation and three-dimensional variable range hopping fit our data properly. One of the two models dominates either at high or low temperature. On the other hand, Au nanowire instead of an electron-beam deposited metal electrode is used as another metal electrode on ZnO nanowire to study the interface effect on nanoscale. The nanoscale contact effect is similar to Schottky type contact and it can be explained by thermionic emission theory while, through our data analyses, it reveals an unexpectedly low Schottky barrier. The barrier height modulation at various applied voltages may be owing to the image-force correction. Through fitting to our data, the contact area between Au and ZnO nanowires, and the carrier concentration of ZnO nanowire can be evaluated. Moreover, we found that the effective barrier height decreases with a decrease of the nanoscale contact area.