硒化鉛奈米顆粒之電性傳輸機制研究

Abstract

本實驗的目的為深入的了解顆粒間波函數疊合程度、表面形貌、及量子侷限效應對於奈米顆粒電性傳輸的影響。藉由改變奈米顆粒間距、顆粒形狀、顆粒尺寸，逐項分析出各項變因在電性傳輸中所扮演的角色。實驗方式為觀察奈米顆粒元件的電流對電壓關係、電阻對溫度關係、背閘極電壓影響、及光激發行為，搭配以電子顯微鏡量測顆粒的形貌及排列，分析其電性傳輸機制。結果中發現調整奈米顆粒間距前後，可觀察到劇烈的電阻變化，甚至於球體奈米顆粒的實驗中會改變電性傳輸機制，例如因顆粒間距變化發生安德森轉換。經分析後八面體與球體奈米顆粒的傳輸行為分別為熱擾致穿隧傳導及跳躍傳輸，造成此差異的原因在於八面體奈米顆粒表面上存在尖端或銳邊，使顆粒間的等效電容極小，使熱擾電壓上升進而降低了顆粒間的位能障。然而球體奈米顆粒間的有效接觸面積較大，顆粒間的電容較大，熱擾電壓較小，因此可排除表面結構對電性的影響，觀察電子於顆粒與顆粒間以跳躍傳輸方式移動。顆粒尺寸方面，發現顆粒大小造成的量子侷限效應在尺寸較小的球體顆粒中扮演重要角色，尺寸的分布使得奈米顆粒的基態能量產生差異，此基態能量的亂度是造成安德森侷域化的重要原因。藉由量測閘極效應，分析出了不同顆粒間距下的遷移率及載子濃度。透過照光實驗，觀察到光反應強度與溫度、顆粒間距、電壓間的關係。

To understand the electrical properties of PbSe nanoparticle (NP), especially the impacts from wave function overlap, surface topography, and quantum confinement, we modulate the interparticle distance, topography and size of nanoparticle and measure the electrical properties. By observing the current to voltage, resistance to temperature relations, gate effect, photoresponse, and surface topography of nanoparticle device, systematic analysis of electronic transport and optoelectronics property can be carried out. The resistance of NP device varies over orders when the interparticle distances change. Moreover, even the electronic transport mechanism changes during the modulation of interparticle distance. For the dependence of NP topography, it was found that, the transport mechanisms are fluctuation induced tunneling conduction and hopping in the octahedral and spherical NP devices, respectively. This difference can be contributed to the difference of interparticle capacitance. The size of NP is also important, especially for the smaller NP, the quantum confinement original from the small size of NP is the main reason of Anderson localization present. From gate dependence, the mobility and carrier concentration of NP device with various interparticle distances is extracted. The photoresponse of NP is also carried out.