奈米磁性與半導體材料複合元件之光電特性研究

Novel optoelectronic properties based on nanostructured magnetic materials and semiconductors composites

陳儒瑩(Ju-Ying Chen)

指導教授 ： 陳永芳

國立臺灣大學/理學院/物理研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.10208

摘要

在本論文中，我們利用不同的磁性材料與半導體材料搭配製作成樣品，並探討其光電特性及在光電元件上的應用。結合磁性材料的許多有趣特性，使半導體光電元件有更多新穎的特性、應用的價值和發展的空間。我們相信結合跨領域的知識及材料，能開發出半導體光電元件更多突破傳統的特性及應用方式。本論文共包含四個主題，其摘要如下：
1. 室溫下高效率之氮化銦鎵/氮化鎵奈米柱自旋發光二極體
過去由於快速自旋弛豫的關係，氮化銦鎵/氮化鎵的自旋發光二極體的輻射旋光度一直無法有重大的突破。我們將氮化銦鎵/氮化鎵薄膜多重量子井蝕刻為奈米柱多重量子井，減少因為晶格常數不匹配所造成的應力，進而降低量子井內的快速自旋弛豫。同時我們在奈米柱間填入四氧化三鐵奈米小球，藉由四氧化三鐵半金屬材料特殊的能帶結構，使量子井中自旋向下的電子會流入四氧化三鐵奈米小球，自旋向上的電子仍留在量子井中。由這種新的機制能有效控制量子井中電子自旋的方向，再加上由鐵磁性金屬電極自旋注入的效果，達到了極高的效率。這樣的設計同時具有許多優勢，能夠在常溫及低磁場下達到10.9 %的輻射旋光度，這個結果遠超過目前其他文獻的氮化物自旋發光二極體的表現。
2. 本身能自旋極化的紫外光旋偏振雷射
承接上個主題，我們利用結構整齊的六角形氮化鎵奈米柱製作出具有回音廊模態的共振雷射，並灑上四氧化三鐵奈米小球，藉由氮化鎵能帶和四氧化三鐵半金屬材料特殊的能帶結構相互搭配，使氮化鎵奈米柱內的電子在受到光激發時會和四氧化三鐵能階重新達到平衡，自旋向下的電子會流入四氧化三鐵奈米小球，自旋向上的電子留在氮化鎵奈米柱中，使氮化鎵奈米柱中的電子自旋方向自發性的被極化。利用這種全新的機制，我們能用非常簡單的方法做出紫外光的圓偏振雷射，這是目前主流的砷化銦鎵/砷化鎵量子井的垂直共振腔面射型雷射所做不到的。
3. 利用磁場控制鐵鈷/氧化鎳之半球殼陣列之光子晶體能隙
我們在單層、具有良好週期性排列的聚苯乙烯小球陣列上蒸鍍上鎳薄膜，再以450 的溫度做熱退火的處理。因為熱退火的溫度高於聚苯乙烯小球的沸點，熱退火處理後可以得到氧化鎳的半球殼陣列。濺鍍鍍上鐵鈷薄膜之後，成功製作出鐵鈷/氧化鎳之半球殼陣列。這個二維的磁性光子晶體陣列排列整齊、有明顯的光子晶體禁帶。我們能透過調變外加磁場的大小改變鐵鈷/氧化鎳之光子晶體禁帶。這個有趣的現象是歸因於隨著磁場變化成線性變化之鐵鈷的介電常數。我們相信這個結果開啟了光子晶體之磁光元件的可能性。
4. 可利用光學控制並偵測氮化銦鎵/氮化鎵多層量子井中的磁電效應
我們在氮化銦鎵/氮化鎵多層量子井/鐵磁性薄膜的複合材料中發現了ㄧ種新的、可由光控制並偵測的磁電效應。我們結合了鐵磁性薄膜可由磁場調變的磁伸縮特性，以及氮化銦鎵/氮化鎵多層量子井中可由光控制的的壓電效應，成功做出了一個新的具良好磁電特性的複合系統。並由於氮化銦鎵/氮化鎵多層量子井的特性，我們更進一步，使用光學的方法來控制及偵測磁電效應，我們相信這個結果對發展磁電效應的應用會有很大的幫助。

關鍵字

自旋弛豫 ； 四氧化三鐵 ； 發光二極體 ； 回音廊模態 ； 垂直共振腔面射型雷射 ； 光子晶體 ； 磁電效應 ； 磁伸縮效應 ； 壓電效應

並列摘要

In this thesis, we have designed, fabricated, and characterized several new nanocomposites based on nanostructured semiconductors and magnetic materials. Many intriguing properties have been discovered, which does not only open new routes for academic interest, but also should be very useful for the generation of novel optoelectronic devices. The thesis contains four main topics, and the highlight of our scientific achievement is briefly described as follows.
1. Efficient spin light emitting diodes arising from InGaN/GaN quantum disks at room temperature: A new self-polarized paradigm
A well-behaved spin light emitting diode (LED) device composed of InGaN/GaN multiple quantum disks (MQDs), ferromagnetic contact and Fe3O4 nanoparticles has been designed, fabricated and characterized. The electroluminescence (EL) spin polarization can achieve a high value of 10.9% at room temperature in a low magnetic field of 0.35 T, which overcomes the difficulty of very low efficiency of spin injection in nitride semiconductors. Several underlying mechanisms play a significant role simultaneously in the new designed device for the achievement of such a high performance. The internal strain in the planar InGaN/GaN MQWs structure is relaxed in the nanodisk formation process. Additionally, the vacancy between nanodisks can be filled by magnetic nanoparticles with suitable energy band alignment for spin up and spin down electrons, which enables the transfer of selected spin between nanodisks and nanoparticles. Unlike previously reported mechanisms, this new process leads to a weak dependence of spin relaxation on temperature. Our approach can open up a new route for the further research and development of semiconductor spintronics.
2. Self-polarized ultraviolet spin-nanolasers
Self-polarized ultraviolet spin-nanolaser has been demonstrated based on periodic GaN nanorods arrays and Fe3O4 nanoparticles. The hexagonal crosssection of GaN nanorods forms natural laser cavities. The self-polarized spin laser action arises from the unique energy band between GaN nanorods and Fe3O4 nanoparticles for spin up and spin down electrons, which enables the transfer of electrons with a particular spin orientation from nanorods to nanoparticles. It therefore spontaneously generates the population unbalance of spin down and spin up electrons in GaN nanorods. This new mechanism does not require electrical pumping by magnetic electrode or optical pumping by circularly polarized light source shown in all previous reports, so that the rigorous restriction of spin-lasers on material selection can be relaxed. A high degree of circular polarization of spin-nanolasers up to 28.2 % can be achieved at room temperature in a low magnetic field of 0.35 T. These efficient spin-nanolasers could have myriad applications, including quantum information, optical communication, and spin optoelectronics.
3. Magnetic Field Modulation of Photonic Band Gap on FeCo/NiO Half-Shell Array
FeCo/NiO half-shell arrays were fabricated based on the periodic monolayer polystyrene spheres. The two dimensional magnetic periodic arrays form well-defined photonic crystals with pronounced stop bands. Quite interestingly, it is found that the stop bands can be tuned by an external magnetic field. The underlying mechanism is attributed to the controllable dielectric constant of the magnetic FeCo film under an applied magnetic field. The results shown here may open up an avenue for magnetically tunable photonic crystal stop bands, which may be useful for the creation of new magneto-optical devices.
4. Optically tunable and detectable magnetoelectric effects in the composite consisting of magnetic thin films and InGaN/GaN multiple quantum wells
An optically tunable and detectable magnetoeletric (ME) effect has been discovered in the composite consisting of InGaN/GaN multiple quantum wells and magnetostrictive ferromagnetic Ni or FeCo thin films at room temperature. Due to the interactively optical and piezoelectric properties of nitride semiconductors, this composite provides an intriguing optically accessible system, in which the magnetoelectric effect can be both easily tuned and detected. The underlying mechanism can be well accounted for by the interplay among magnetostrictive, piezoelectric and optical transition. It thus offers a new paradigm to generate artificial material systems with magnetic/electric/optical inter-related/controllable properties.

並列關鍵字

Fe3O4 ； LED ； Whispering Gallery Mode photonic crystal ； magnetoeletric effect ； magnetostrictive effect ； piezoelectric effect

參考文獻

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