Optical properties of GaN Photonic Crystal Membrane Nanocavities at Blue Wavelengths
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0892-FF20-06.1
Optical properties of GaN Photonic Crystal Membrane Nanocavities at Blue Wavelengths Yong Seok Choi1, Cedrik Meier1, Rajat Sharma2, Kevin Hennessy1, Elaine D. Haberer2, Shuji Nakamura2, and Evelyn L. Hu1,2 1 Departments of Electrical and Computer Engineering and 2 Materials Department University of California, Santa Barbara, CA 93106, U.S.A ABSTRACT We have investigated the design parameters for high-Q photonic-crystal (PC) bandgap modes in the emission wavelengths of InGaN/GaN multiple quantum wells. We demonstrate experimental schemes to realize 2D triangular-lattice PC membrane structures, which is essential to obtain photonic bandgap (PBG) modes, and the optical properties of L7 membrane nanocavities that consist of seven missing holes in the G-K direction. L7 cavities show pronounced resonances with Q factors of 300 to 800 in the PBG as well as the enhancement of light extraction of the broad InGaN/GaN multiple-quantum-well emission by the 2D PBG. INTRODUCTION Photonic crystals (PCs) have given rise to much researches for various applications from manipulating the optical process of embedded emitters [1] to realizing the novel nano-photonic circuitry [2]. High-Q PC nanocavities may be the best candidates to achieve low-threshold lasers in GaN material systems [3] with a potential for integration with other nanophotonic devices. Various PC structures embedded in light emitting diode enhance the extraction efficiency, demonstrating the merits of PCs [4]. Furthermore, high-Q 2D PC nanocavities with GaN-based quantum dots (QD) [5] will facilitate the study of cavity quantum electrodynamics [6] and single photon sources [7] at room temperature with the virtue of the deep confinement resulting from the large GaN bandgap. The realization of GaN-based high-Q PC nanocavities poses a number of challenges. The short emission wavelength requires higher precision lithography and etching techniques than what are required for the longer wavelength materials such as GaAs or InP-based PCs. To achieve photonic bandgap (PBG) modes in the low refractive index ( n ≅ 2.6 ) GaN materials, it is essential to use free-standing membrane structures. Recently, a bandgap-selective photoelectrochemical (PEC) wet etching process has been developed to produce high quality microdisk resonators [8] and air-gap distributed Bragg reflectors [9]. However, techniques for well-controlled, selective, and low damage processing methods are yet to be developed.
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DESIGN PARAMETERS The L7 PC membrane nanocavity consists of seven missing holes in the G-K direction of 2D triangular-lattice PC structures. The resonance modes are determined by the PC waveguide dispersion as well as the Fabry-Perot condition. Among various resonances, we are interested in the lowest-energy even mode as it ensures good spatial overlap with the active region (in comparison with the air hole regions) and a high-Q factor of 104 in the mode volume of 1.3µ(l/n)3 [10]. The resonance wavelength can be lithographically tuned by changing the lattice cons
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