利用原子層沉積技術成長氧化鋅鎂薄膜及其發光二極體之研究

Characteristics of MgxZn1-xO Thin Films and MgZnO Based Light-Emitting Diodes Grown by Atomic Layer Deposition

黃郁勛(Yu-Hsun Huang)

指導教授 ： 陳敏璋

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10947

摘要

本論文係研究原子層沉積技術成長之氧化鋅鎂薄膜及其發光二極體之光電特性，其內容可分為三個部分。首先，本研究成長不同比例之氧化鋅鎂薄膜於藍寶石基板。研究結果指出，鎂元素成分大於10% 的薄膜在熱處理之後會產生相分離的情形。光激發光 (photoluminescence) 實驗顯示，鎂的摻雜會使氧化鋅鎂薄膜於室溫下的自發輻射 (spontaneous emission) 波長由378 奈米藍位移至346 奈米，代表其能隙隨著鎂的摻雜而變大。同時，溫度上升對其發光強度的影響亦隨之減弱。另外，含10% 鎂元素之氧化鋅鎂薄膜在室溫下的受激輻射 (stimulated emission) 閾值約為280 kW/cm2。由以上實驗結果可以得知，原子層沉積技術成長之氧化鋅鎂在能隙工程 (band gap engineering)與發光元件之應用上具有極佳的潛力。
接著，本研究成長氧化鋅鎂薄膜於p型氮化鎵上並製作 n-Mg0.10Zn0.90O/p-GaN 以及 n-ZnO/Mg0.1Zn0.9O/p-GaN 兩種發光二極體。前者於逆向偏壓下顯示出由 370 奈米紫外光主導之電激發光 (electroluminescence) 頻譜，後者於逆向偏壓則是以 425 奈米之藍光為主，此兩種波段的光均源自於p型氮化鎵。利用能帶結構與理論模型分析可得，上述兩個發光二極體於逆向偏壓下的發光是由電子穿隧效應所導致。
最後，本研究成長氧化鋅薄膜於氧化鋅鎂上形成 Mg0.1Zn0.9O/ZnO 異質結構。研究結果指出後續退火處理對其結構及光學性質並無有效的改善。此外，當氧化鋅薄膜厚度小於10奈米時，其近能隙 (near band edge) 發光會由 378 奈米藍位移至 366 奈米。推測其原因可能為異質結構中的量子效應以及氧化鋅層中的應力效應共同導致之能隙變化。

關鍵字

原子層沉積技術 ； 氧化鋅鎂 ； 發光二極體 ； 電子穿隧 ； 應力 ； 量子效應 ； 藍位移

並列摘要

In this thesis, we present the characteristics of the MgxZn1-xO thin films and MgZnO based light-emitting diodes (LEDs) grown by atomic layer deposition (ALD). The contents can be divided into three topics.
In the first topic, the effects of Mg doping on the structural and optical properties of MgxZn1-xO thin films grown by ALD and treated by RTA were investigated. Solubility limit of MgO in the MgxZn1-xO is reached when x = 0.10. The near-band-edge (NBE) photoluminescence (PL) of MgxZn1-xO thin films exhibits blue-shift from 378 nm to 346 nm. Thermal quenching of the PL intensity is also suppressed by the incorporation of Mg into ZnO, In addition, the threshold of stimulated emission in the Mg0.1Zn0.9O film is about 280 kW/cm2. These results indicate that the MgxZn1-xO film grown by ALD is a potential material for band gap engineering and light-emitting devices.
In the second topic, electroluminescence (EL) from n-Mg0.10Zn0.90O/p-GaN and n-ZnO/Mg0.1Zn0.9O/p-GaN hetrojunction LEDs at reverse breakdown bias were investigated. An UV light at 370 nm dominates the EL spectrum from the n-Mg0.10Zn0.90O/p-GaN heterojunction LED. On the other hand, the EL spectrum of the n-ZnO/Mg0.1Zn0.9O/p-GaN hetrojunction LED showed a dominant blue light (425 nm) emission. It was supposed that the electrons tunnel via deep-level states from the valence band in p-type GaN to the conduction valence band n-type ZnO for both devices, which was confirmed by a theoretical model based on the electron tunneling.
In the last topic, the optical properties of the Mg0.1Zn0.9O/ZnO/Al2O3 heterostructures grown by ALD were domonstrated. The optical and structural analyses indicate that the annealing treatment has no improvement in the quality of the Mg0.1Zn0.9O/ZnO heterostructure. When thickness decreases from 50 nm to 5 nm, the NBE PL from the ZnO layer shifts from 378 nm to 366 nm, which may be attributed to the quantum confinement and strain effect in the ZnO layer.

並列關鍵字

atomic layer deposition (ALD) ； MgZnO ； light emitting diode ； electron tunneling ； stress ； quantum effect ； blue shift

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