探討硫化鉛奈米線與碳六十電性傳輸

Abstract

本實驗利用變溫量測方式量測硫化鉛奈米線以及C60顆粒。硫化鉛奈米線的電性透過對元件進行變溫量測，發現溫度變化範圍內，電阻隨著溫度下降而上升，即有負溫度係數(dR/dT<0)，因此呈現半導體特性。實驗結果藉由熱活化能傳輸與Mott變程跳躍理論這兩種模型並聯來分析奈米線特性，並且在低溫區閘極會隨溫度下降而雙載子行為越來明顯。其中變程跳躍R∝exp⁡(〖T_0/T)〗^(1/(d+1))(d為系統維度)，晶體結構導電特性可視為一無序系統下，載子在局域態間透過聲子激發作用達到傳輸的功能。 而透過熱游離分析可知，樣品因蕭特基接觸造成蕭特基位障，將隨著偏壓增加而位障降低。而C60顆粒的電性傳輸，透過熱退火使電阻值下降可使我們進一步分析元件傳輸機制，經由在低溫分析下主要以三維變程跳躍方式傳輸，推測是C60顆粒與顆粒之間的自組裝使晶體的導電性越好，而元件顆粒自組裝產生無序系統，因此符合變程跳躍模型而其中因樣品的大小相對為巨觀傳導，因此為三維變程跳躍。

Abstract In this study, the electron transport in PbS nanowires is studied from temperature behaviors of current-voltage (I-V) curves in the temperature range between 80 and 300 K. PbS nanowire devices reveal a negative temperature coefficient resistance and display semiconducting behaviors. PbS nanowire devices exhibit thermally activated transport and three-dimensional Mott’s variable range hopping at high and low temperatures, respectively. It proposed that, due to the lattice disorder in PbS nanowires, electrons are localized thus electron transport in nanowires follow variable range hopping conduction. The I-V curves of PbS nanowire devices show nonlinear and asymmetric features. They can be fitted with thermionic-emission theory, implying a Schottky contact between the PbS nanowire and the metal electrode. In addition to studying disorder effect in nanowires, we try to see the same effect in the molecule-assembled bulk. The fullerene of C60 molecules is selected for this study. C60 molecules are assembled to form a piece of bulk sitting in the gap between two metal electrodes. The C60 devices are annealed at 400⁰C for 6 hours in a high vacuum to reduce the resistivity. The electrical properties are then measured. Electron transport in C60-assembled bulk can also be described by three-dimensional Mott’s variable range hopping in the temperature range between 25 and 300 K.