以水熱合成法於氮化鎵基板上製備穩定形貌之氧化鋅奈米柱

Fabrication of Stable-Morphology ZnO Nanorods on GaN by Hydrothermal Synthesis

李權祐(CHUAN-YU LEE)

指導教授 ： ?武義

中原大學/電機資訊學院/電子工程學系/碩士(2023年)

https://doi.org/10.6840/cycu202301097

摘要

氧化鋅(ZnO)相較於氮化鎵(GaN)有略小的能隙3.37 eV，具有高機械性、熱穩定性、良好導電性，特別是它高於氮化鎵(25 meV)的激子束縛能(60 meV)，在室溫環境下可充分利用激子來發光，因此可廣泛運用，包括紫外線雷射、發光二極體、場發射元件、化學感測器、光伏太陽能電池等。
本研究使用低成本的水熱合成法(hydrothermal synthesis)於GaN基板上成長ZnO奈米柱，期以穩定形貌ZnO奈米柱結構提升GaN基板發光效率。研究中藉由調變六亞甲基四胺(HMTA)和醋酸鋅(固定1:1比例)混和溶液濃度、成長時間與溫度等參數進行實驗並結合快速熱退火(rapid thermal annealing, RTA)處理，以尋求GaN基板上ZnO奈米柱製備條件的優化。所製備出的樣品同時使用掃描式電子顯微鏡(scanning electron microscope, SEM)及光致發光(photoluminescence, PL)光譜儀，探討奈米柱形貌與發光特性的相關性；其中在PL特性分析方面分別進行了變溫與變激發功率量測以確認ZnO發光機制。
由研究結果得知，使用0.075 M成長溶液於90 °C下成長4小時可得相對密集且均勻ZnO奈米柱結構；其室溫UV波段與可見光波段之PL強度比可達數十倍以上。另外變溫PL量測結果指出D0X機制主導整個低溫下的發光光譜，同時利用接近室溫的PL積分強度變化對於D0X的束縛能進行了估計；至於變功率PL量測結果則為源自奈米柱結構所致激子發光性質提供了佐證。

關鍵字

水熱合成法 ； 氧化鋅 ； 奈米柱 ； 快速熱退火 ； 變溫與變功率光致發光

並列摘要

Compared with gallium nitride (GaN), zinc oxide (ZnO) has a slightly smaller energy gap of 3.37 eV. It has high mechanical properties, thermal stability, and good conductivity, especially its exciton binding energy (60 meV) is higher than that of gallium nitride (25 meV). Therefore, the excitonic emissions at room temperature can be widely used for the applications of ultraviolet lasers, light-emitting diodes, chemical sensors, photovoltaic solar cells, and so on.
This study uses a low-cost hydrothermal synthesis method to grow ZnO nanorods on GaN substrates. It is expected to improve the luminous efficiency of underlying GaN substrate with a ZnO nanorod structure prepared on top.
The experimental parameters including: the concentration of the mixed solution of hexamethylenetetramine (HMTA) and zinc acetate (fixed at the ratio of 1:1), growth time and temperature are optimized, accompanied by a rapid thermal annealing (RTA) treatment to prepare stable-morphology ZnO nanorods on GaN substrates. Both scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy were used to explore the correlation between surface morphology and luminescence characteristics for the nanorod structures prepared. In particular, the temperature dependent and excitation power dependent PL measurements were simultaneously conducted to confirm the detailed luminescent mechanisms of ZnO nanorods.
According to the research results, a relatively dense and uniform ZnO nanorod structure could be achieved by using 0.075 M growth solution to grow at 90 °C for 4 hours; for such a specimen the PL intensity ratio of the UV band to the visible band measured at room temperature reached more than dozens of times. In addition, the temperature dependent PL measurement results indicated that the mechanism of neutral-donor-bound exciton (D0X) recombination dominates the luminescence spectrum at low temperatures, and also the binding energy of D0X could be estimated by using the variation of PL integral intensity close to room temperature. On the other hand, excitation power dependent PL analysis provided evidence for the excitonic emission properties derived from the nanorod structure.

並列關鍵字

Hydrothermal synthesis ； ZnO ； Nanorod ； Rapid thermal annealing ； Temperature and excitation power dependent photoluminescence

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