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標題: | 二維光子晶體對非極性氮化鎵發光二極體之光學特性探討 Properties of Optical Emission with Two-dimensional Photonic Crystals on the Non-polar GaN Light-emitting Diodes |
作者: | Hsiang-Wei Li 李祥瑋 |
指導教授: | 黃建璋 |
關鍵字: | 發光二極體,非極性氮化鎵,a-晶面氮化鎵,光子晶體,發光場形,光子晶體能帶,偏振極化光,Purcell effect,光萃取效率, light-emitting diode,non-polar GaN,a-plane GaN,photonic crystals,radiation profile,photonic band,polarized emission,Purcell effect,extraction efficiency, |
出版年 : | 2014 |
學位: | 碩士 |
摘要: | 相較於極性氮化鎵發光二極體,非極性氮化鎵擁有著獨特的光學特性,其所發出的光具有線偏振特性,使得發光二極體有更多方面的應用,像是能夠成為液晶顯示系統的背光源而不需要偏振片,能夠減少發光強度的減損,提升光的輸出效率。為了更加提升非極性氮化鎵發光二極體的光偏振性,其中可藉由製作光子晶體結構來增加極化光的萃取,本篇論文主要研究二維光子晶體對於a-晶面(非極性)氮化鎵發光二極體的光學特性探討。
在第一部份研究,我們製作二維光子晶體結構在a-晶面氮化鎵發光二極體上,量測其光學特性的變化。在量測的光子晶體能帶中,電場平行m軸的光(E//m極化光模)受到強烈的群速度變化,使得大量提升其光的強度;相對的,電場平行c軸的光(E//c極化光模)則沒有這種現象,因此其光強度被光子晶體結構萃取的相對較少。除此之外,為了更加了解光的偏振性與E//m極化光模的繞射特性之間的關聯,我們藉由觀察量測結果所得到的偏振比例輪廓圖,發現其所產生強烈群速度變化的位置與E//m極化光模的繞射光子晶體能帶相符合,此結果證明光的偏振比例提升是因為藉由光子晶體萃取強烈E//m極化光模所達成。 在第二部分的研究中,我們一樣製作二維光子晶體結構在a-晶面氮化鎵發光二極體表面上,然而光子晶體的週期重新設計。在整體光強度量測中,藉由光子晶體能提高光的輸出,然而在光偏振強度以及發光場型的量測上,發現E//m極化光模和E//c極化光模有著不同程度的強度提升,光子晶體大量提升E//m極化光模的強度,使得發光的偏振性增加。為了了解此光子晶體對於不同極化光模的強度增加特性,我們研究光子從產生到被光子晶體結構萃取的過程,並由結果發現電場與不同光子晶體週期繞射,會產生不同的光萃取程度。除此之外,在光子晶體結構中,相對於E//c極化光模,E//m極化光模的自發性發光輻射率會被提升,此現象可由Purcell影響所解釋,主要原因為原本E//m和E//c極化光模的載子復合機率不同,使得發光輻射率有不同程度的影響。並且,我們討論Purcell影響在光子晶體結構中,對於極性和非極性氮化鎵的作用,發現Purcell提升效率,一方面會受到光子晶體的結構影響外,也會受到材料本身的晶格特性所改變。 Due to the intrinsic properties of non-polar GaN light-emitting diodes (LEDs), generation of the polarized light makes the more applications. In order to increase the polarized emission in non-polar GaN LEDs, photonic crystals (PhCs) are employed for the extraction of the polarized photons. In the thesis, the interaction between the PhCs and non-polar GaN LEDs is studied. In the first part, the two-dimensional PhCs were fabricated on a-plane GaN LEDs. According to the anisotropic polarized emission in a-plane GaN LEDs, the PhCs were aligned with the specific axes to enhance the degree of polarization. The measured photonic bands show the strong diffraction of E//m modes as compared with that of E//c modes along both a-c plane and a-m plane. Furthermore, the correlation between the degree of polarization and E//m mode photonic bands is studied. The similar locations of the band crossings are presented both in the polarization ratio contours and the related photonic bands of E//m modes. The results indicate that the degree of polarization is enhanced by the main diffraction of E//m modes with the PhCs. Thus, the polarized emission and the light extraction of a-plane GaN LEDs can be improved by the PhCs. In the second part, by means of the two-dimensional PhCs with different periods on the surface of a-plane GaN LEDs, the total light output is enhanced. However, the extraction of E//m modes is larger than that of E//c modes, leading to asymmetric enhancements in the PhC LED. For realization of the PhC effects, the model was established. The results show that extraction efficiencies are different with regard to E//m modes and E//c modes. The extraction of E//m modes is more efficient as compared with that of E//c modes because of the different period design in the PhCs. In addition, Purcell effect exhibits the different emission rate enhancement according to the transition rate in the corresponding valence bands. In a-plane GaN PhC LED, the spontaneous emission rate of E//m modes is mainly improved, making the large generation of E//m photons over E//c photons by Purcell effect. Moreover, we discuss Purcell effect of the PhCs on polar and non-polar GaN, and observe that Purcell enhancement is not only changed by the PhC structure but also influenced with the crystal property of the material. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/57011 |
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