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In this paper, nonpolar a-plane GaN-based photonic crystals (PCs) with different defect cavities have been demonstrated. By using a micro-photoluminescence ( -PL) system operated at 77 K, the dominant resonant modes of the GaN-based PC defect cavities show high quality factor (Q) va lues in the light emission performance which can be up to 4.3 H10 3 . Moreover, the degree of polarization (DOP) of the light emission from the nonpolar GaN-based PC defect cavities was measured to achieve around 64 % along the m crystalline direction. Keywords- GaN, nonpolar, a-plane, photonic crystal, defect cavity. 1. INTRODUCTION Photonic crystals (PCs) with defect cavities have been widely investigated and applied in advanced lasing devices owing to their significant photonic bandgap effect, which can be sufficiently employed to realize the photon confinement in a small mode volume and light emission with high quality factor (Q) values [1-4]. By changing the defect cavity parameters such as the cavity types, radius of constituent nanoholes, lattice constants, and the material compositions with different refractive indices, specific light emission characteristics could be acquired and employed in many applications such as the ultra-low threshold lasers and photonic integrated circuits [5-13]. Among the great efforts made previously in the development of PC defect cavity lasers, most the studies were reported using GaAs and InP-based materials because the suspended thin membrane structures which are beneficial to achieve high Q values can be easily made by selective chemical etching to remove the underneath sacrificial layer [1,2]. However, some unwanted damages and composites cannot be avoided during the reaction process. Recently, GaN-based materials have attracted much attention and been considered as a competitive material for exploring next-generation optoelectronic devices. GaN-based materials exhibit many promising properties such as high exciton binding energy and oscillator strength which is beneficial for supporting high efficiency light emission and exciton-photon coupling capabilities. However, the PC defect cavity lasers based on the use of GaN-based materials were seldom addressed because of the relative challenging etching process in the thin membrane structures fabrications. Several feasible methods have been proposed such as the photo-electro-chemical (PEC) etching of InGaN sacrificial layers [14-17], selective chemical wet-etching of InGaN layers grown on Si substrate [18,19] and selective thermal decomposition of GaN layers [20]. Nevertheless, it is still a challenge to fabricate GaN-based membrane structures due to the complex etching process of particular epitaxial structures. Although the fabrication of a thin membrane structure is relatively difficult in the GaN-based system, the quest to demonstrate a GaN-based PC defect nanocavity laser is still fa scinating, especially for the nonpolar GaN-based materials. The main characteristic of nonpolar GaN is free of polarization fields in the quantum wells which can lead to high internal quantum efficiency and fabrication flexibility [21-26]. Furthermore, nonpolar GaN-based materials can exhibit the anisotropic gain in the m -axis or a-axis which is beneficial for development of low threshold and high power lasers [27-29]. |
