Optoelectronic Properties of III-Nitride Semiconductors
在本論文中, 我們提出了氮化物半導體之光學與電學的研究,其中包含氮化銦鎵磊晶薄膜, 氮化銦鎵/氮化鎵多重量子井結構, 氮化銦鎵/氮化鎵超晶格, 氮化鋁鎵/氮化鎵超晶格以及氮化銦鎵/氮化鎵奈米針. 內容如下:
藉由光激發螢光,電子掃描顯微鏡, 電子束螢光, 穿透式電子顯微鏡等量測研究出鎂摻雜氮化鋁鎵/氮化鎵超晶格光學特性與結構的關係. 我們發現側面的藍色能帶有光學異向性. 經由電子束螢光, 穿透式電子顯微鏡等量測研究我們可知鎂摻雜所形成的三角錐缺陷是造成光學異向性的來源.
我們藉由奈米針的製程讓發光二極體增加其發光效率. 藉由我們的研究,我們清楚的確認奈米針可以增加發光效率是來自藉由這個製程應力被釋. 對於許多有存在應力的半導體材料中,我們的結果將對於未來發展高效能的光電元件更有幫助.
我們記錄了氮化銦鎵/氮化鎵超晶格在沒有外加磁場, 只外加電流引發自旋異向性的研究. 除此之外, 電旋獲爾效應可被內部應力控制也已經被發現. 此結果也有理論計算來佐證.
藉由XRD, 電子掃描顯微鏡, EDS, 電子束螢光等實驗,光學與結構特性的修正提供了一個直接的證據支持銦奈米柱是主導其發光來源.我們的結果對於將來光電元件發光效率的增加可提供 一個重要的貢獻.
關鍵字: 光激發螢光, 氮化銦鎵/氮化鎵, 拉曼
In this thesis, we perform several studies of electrical and optical properties of nitride-based semiconductor heterostructure, including InGaN thin film, InGaN/GaN multiple quantum wells, InGaN/GaN superlattices, AlGaN/GaN superlattices, and InGaN/GaN nanotips. These results are presented as follows.
The structural and optical properties of Mg-doped AlGaN/GaN superlattices have been investigated by photoluminescence (PL), scanning electron microscopy (SEM), cathodoluminescence (CL) and transmission electron microscopy (TEM). We found that the edge blue-band emission shows a strong optical anisotropy. Through the combination of the CL and TEM images, we clearly establish that the underlying microstructure responsible for the blue luminescence in Mg-doped AlGaN/GaN arises from the pyramidal defects.
We have reported an intriguing photoelastic effect in InGaN QDs for the first time. The optically modulated internal strain contributes to the blueshift in edge PL spectra, a reduction of the refractive index, and a redshift in the InGaN LO phonon mode. In addition, the change of the temperature dependence of the PL emission energy under high and low excitation density can also be explained consistently.
We have demonstrated a significant improvement of the emission from InGaN/GaN nanotip arrays compared with InGaN/GaN MQWs. The nanotip arrays were formed by a simple and low cost self-masked dry etching process, which is compatible with the current semiconductor technologies. Our unique approach is able to enhance the light output power by a factor of up to 10 times. Based on our study, we clearly demonstrate that the main underlying mechanism for the enhanced luminescence arises from the strain relaxation in the nanotip through its inherent characteristic of a large surface-to-volume ratio.
Lateral current-induced spin polarization in InGaN/GaN superlattices (SLs) without an applied magnetic field is reported. The fact that the sign of the nonequilibrium spin changes as the current reverses and is opposite for the two edges provides a clear signature for the spin Hall effect. In addition, it is discovered that the spin Hall effect can be strongly manipulated by the internal strains. A theoretical work has also been developed to understand the observed strain-induced spin polarization. Our result paves an alternative way for the generation of spin polarized current.
The correlation between optical and structure properties obtained by XRD, SEM images, EDS, and localized CL spectra provides a direct and concrete evidence to support the fact that the formation of nanoclusters is responsible for the enhanced luminescence in InGaN thin films. Our results shown here can serve as an important clue for the enhancement of the luminescent intensity in future optoelectronic devices.
Key words : PL, InGaN/GaN, Raman
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