Properties of Optical Emission with Two-dimensional Photonic Crystals on the Non-polar GaN Light-emitting Diodes
Date Issued
2014
Date
2014
Author(s)
Li, Hsiang-Wei
Abstract
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.
Subjects
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
Type
thesis
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