Ultrahigh quality factor in a metal-embedded semiconductor microdisk cavity

Abstract

We numerically and theoretically investigate electrodynamics of a metal-embedded semiconductor microdisk cavity. The electrodynamics of a cavity mode is discussed from the viewpoint of quantum mechanics, which clarifies the condition for high Q factor. Using numerical calculation, we optimize the cavity structure and show that the Q factor can be increased up to 1,700,000. Our study suggests that the metal-embedded cavity is a promising candidate for cavity quantum electrodynamics devices. © Quality factor (Q factor) of cavity has been the focus of interest in optics, photonics and optoelectronics since the Purcell's discovery that spontaneous emission can be controlled by manipulating the photonic density of states with a cavity [1]. Various kinds of cavities have been proposed and demonstrated in order to achieve higher Q factor and smaller mode volume. For example, pillar microcavities based on distributed Bragg reflec-resonators, and photonic crystal cavities [6] are now available as a cavity with high Q factor. Even though these cavities have high Q factors and small mode volumes, whole cavity structures generally occupy a relatively large amount of space compared with operating wavelengths. This relatively large cavity volume is basically due to the property of dielectric open cavities. On the other hand, metallic nanocavites are able to achieve small cavity volumes due to the metallic nature of strong confinement of electromagnetic (EM) fields.Metallic nanocavities have been extensively studied for realizing nanolasers with miniaturized cavity volumes [7][8][9][10][11]. However, the cavity Q factors measured up to now remains low below ∼500 due to significant optical absorption of the constituent metals [7][8][9][10][11]. The metallic nanocavities have also been numerically characterized and the higher Q factors of ∼1700 [12] and ∼ 3400 [13] have been reported. Recently, higher Q factor about 5000 at room temperature [14] and 9000 at 20 K [15] have been demonstrated in a metal-embedded cavity. Although high Q factor in a metallic cavity has been experimentally demonstrated, the generation mechanism of the high Q factor is not fully clarified so far.In this Letter, we present a theoretical and numerical study of high Q factor in a metal-embedded semiconductor μ-disk cavity. The electrodynamics of high Q mode is analyzed from the viewpoint of quantum mechanical particle subject to an effective potential. Using this analysis, we reveal crucial parameters to achieve higher Q factor. Following the theoretical study, we propose an optimized metal-embedded cavity and numerically explore high-Q cavity mode. We demonstrate a cavity mode with an ultra-high Q factor of 1,700,000. Let us consider a metal-embedded cavity shown in Fig. 1. The cavity consists of a homogeneous semiconductor μ-disk with permittivity ε 1 and radius r. We assume that the μ-disk is embedded in a metallic medium with permittivity ε 3 . The metallic material is assumed to have small optical loss in the visible and near infrared regions. We i...

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“…For instance, the photonic crystal (PhC) nano-cavities with ultra-high quality (Q) factors [ 1 ] can confine light into a subwavelength region. Similar to the PhC cavities, high Q factors are realized by micro-disk [ 2 , 3 ], spherical [ 4 ], and troidal [ 5 ] cavities. Those cavities with high Q factors usually consist of transparent dielectric materials.…”