水熱法合成磷摻雜氧化鋅奈米線及其電性量測

Abstract

一維的氧化鋅奈米結構如奈米線、奈米柱、奈米管，由於其特殊結構和幾何形態，因此廣泛用在奈米元件上。而本質為n型的氧化鋅，可透過摻雜調整成p型的材料，增加其發展性。本研究是以醋酸鋅及六亞甲基四胺、五氧化二磷為先驅物，使用水熱法成長磷摻雜氧化鋅奈米線，並進一步利用兩階段合成出以氧化鋅為基底的氧化鋅p-n同質接面奈米線。利用X光繞射儀及穿透式電子顯微鏡進行結構鑑定，發現奈米線p-n同質接面之兩端皆為單晶六方晶系結構，且有相同的成長方向，其成分與元素分布則以X射線能量色散譜與電子能量散失能譜儀進行分析，發現磷的相對含量在界面附近有明顯上升的趨勢，介面兩端之磷原子百分比分別為0.38和2.81%。 電性方面，將合成磷摻雜氧化鋅奈米線製成單根奈米線場效電晶體量測，得到奈米線電阻率約為0.0132Ωcm，且當閘極通負偏壓時，汲極電流上升，明顯為p型半導體傳輸特性；透過兩階段成長的單根和多根p-n同質接面結構都有明顯的整流現象，也間接證明磷摻雜部分確實展現p型特性，並能透過PL做非破壞性偵測。透過低溫PL量測發現，除了近能帶與可見光缺陷波段外，發現在波長416nm及435nm有兩個額外的訊號，是來自於p-n兩端接觸後造成能帶扭曲，電子、電洞於新的能階結合所貢獻。 最後利用穿透式電子顯微鏡搭配環境式載具，臨場觀測水熱法氧化鋅奈米晶體之成長，析出過程大致分為三階段(1)溶質擾動 (2)晶體析出 (3)晶體成長，氧化鋅粒子成長到最大約100奈米左右，且兩相鄰粒子間是否能穩定成長與兩者之距離有關。析出物附近溶質的消耗，會對粒子成長造成影響，將粒徑大小對成長時間做圖，利用斜率判斷其成長速率會下降，屬於擴散控制反應。

Among variety of 1-D materials, ZnO nanowires (NWs) has attracted extensive attention due to its specific physical properties. For wide-ranging applications in nanoscale electronic devices, durable and reproducible p-type ZnO is essential. In this work, pure ZnO NWs were synthesized via the hydrothermal method which used zinc acetate and HMTA mixed solution as the precursor; Additionally, P2O5 was served as a dopant source to obtain p-type ZnO NWs. Simple p-n homojunction device could be grown by two-step synthesis through different solution mentioned above. The morphology of ZnO NWs arrays were examined by field emission scanning electron microscope (FESEM). The high resolution transmission electron microscope (HRTEM) image indicated that the single ZnO NW p-n homojunction is single-crystalline with <001> growth direction. The distribution of P element was analyzed by Energy Dispersive Spectrometer (EDS). In addition, the dynamic growth of ZnO nano particle via hydrothermal method was observed in in-situ TEM. Moreover, the results of temperature-dependent photoluminescence (PL) spectra revealed that both phosphorus-doped and pure ZnO NWs showed a UV light emission (370–380 nm) and a defect-related emission (400–750 nm). It's remarkable that two extra peaks located at 416 nm & 435 nm were discovered from ZnO NW p-n homojunction resulting from donor-acceptor recombination. The electron transport properties and field effect transistors (FETs) of the single phosphorus-doped ZnO NW confirmed p-type conductivity with low resistivity (0.0132 Ω.cm). The single ZnO NW p-n homojunction demonstrated rectification characteristics.