單根氧化鋅及鎵摻雜氧化鋅奈米線之電性傳輸研究

Abstract

對於奈米尺度下的氧化鋅材料，其導電機制一直是重要且被關注的研究課題，在本篇論文中，我們觀察了兩種不同雜質摻雜的氧化鋅奈米線，藉由量測室溫到液態氦溫度範圍的電阻率隨溫度變化關係，以及加入磁場後對電阻的影響，來探討氧化鋅奈米線的導電機制。 我們用四點量測法量測了一系列原生摻雜的氧化鋅奈米線的電阻值，觀察室溫電阻率對應到的載子濃度，發現這三個樣品都很靠近金屬-絕緣體轉變點，在低溫下也有電阻率飽和的情形。我們也由電阻率跟溫度的關係知道原生摻雜氧化鋅奈米線並無變程跳躍的導電機制出現，而是由熱激發和近鄰跳躍這兩種導電機制主導。 另外我們也量測了鎵摻雜氧化鋅奈米線之磁電阻，探討量子干涉效應對電阻值的影響，確定樣品呈現三維的弱局域效應。我們又從溫度的變化關係知道在較高溫時是由電子-聲子散射主導電子的相位相干長度，電子-電子散射的影響則太小可忽略。

The electrical conduction mechanisms in nanoscale ZnO materials are an important and noticeable topic all the time. In this thesis, we have studied natively doped and Ga-doped ZnO nanowires. By measuring the temperature behavior of resistivities from 300 K down to liquid-helium temperatures and the magnetoresistances in low magnetic fields, we address the electrical conduction mechanisms in these nanowires. We performed four-probe measurements on a series of natively doped ZnO nanowires. We found that our nanowires fell very close to the metal-insulator transition. Saturation of resistivity at the very low temperature region was observed. We found no appearance of variable-range hopping conduction. Instead, the combined thermal activation and nearest-neighbor hopping mechanisms dominated the overall temperature behavior of electrical resistivities. In addition, we have measured the quantum-interference magnetoresistances of Ga-doped ZnO nanowires. We found that our nanowires were three-dimensional with regard to the weak-localization effect. The electron dephasing lengths were extracted. We found that, at temperatures above a few degrees Kelvin, the electron-phonon scattering dominated the dephasing, while the electron-electron scattering was negligibly small.