Design and simulation of superperiodic photonic-crystal light emitting diodes with highly directive luminance characteristics

Abstract

By use of finite-differene time-domain analysis for lightwave devices, a novel super-periodic photonic-crystal lightemitting diode (LED) design exhibiting high-luminance patterns is proposed for applications that require highly-directive vertical light extraction. The device design is made on the theoretical consideration on the density of radiation modes within the photonic band coupled with far-field diffraction of the spontaneouslyemitted light from a structure with double periodicity.Photonic crystals (PhCs) are dielectric periodic structures that have great potential for the realization of integrated photonic circuits. With this scope in mind, a significant amount of research efforts has been made in designing and fabricating prototype optical components such as waveguides, channeldrop filters [1], and nano-cavity lasers [2], based on the PhC structure. Especially, some of the most demonstrative PhC devices are designed to utilize the photonic-band gap in the wavelength-vs.-wavevector dispersion diagram.The device principle of such a photonic-band design requires a substantal contrast in the dielectric-constant profile to open up the bandgap that is sufficiently wide. For this reason, semiconductor dielectric materials that are interfaced directly to the air and are interacting with light in the infrared-tovisible range, are usually employed. With such designs, actual devices must be fabricated with the period range of 200-600 nm with the shorter side for those in the visible spectrum.In order to analyze the field theoretic performance of many such nano-scale optical devices, the FDTD simulation is probably the only numerical method that gives reliable results. Historically, the reliability of the method has been greatly enhanced when the so-called perfectly-matched anisotropic layers [3] that had refined the original simpler PML boundary condition [4]. To give the most proper analysis for an active medium that produces light, the FDTD method was further improved with the so-called recursive-convolution technique that was modified to model the gain medium by a single pole [3] interfraced with each perfectly-matched anisotropic layer [5].In the present work currently using the passive version of (a) ρ ρ m (b) Fig. 1. Schematics for (a) the super-periodic PhC plate and (b) its in-plane unit super-cell. Radius ρ of the etched periodic holes is normally set at 0.43 a, except for radius ρm of the outer-most six holes in the defect. These outermost holes are subsequently pulled into the center with distance l. The plate thickness t and the distance between the adjacent defects dc are set at 0.5 a and 4 a, respectively.the FDTD program, we design and numerically demonstrate a high-power light-emitting PhC plate with highly-directive radiation for various applications; displays, lightening, and illumination, etc. To achieve this goal, doubly periodic patterns have been implemented on a simulated GaN plate, as shown in Fig. 1. This design is referred to as a 'super-periodic photonic crystal (super-PhC) with monocell ...