김선경 교수

We studied optical resonances in laterally oriented Si nanowire arrays by conducting finite-difference time-domain simulations. Localized Fabry-Perot and whispering-gallery modes are supported within the cross section of each nanowire in the array and result in broadband light absorption. Comparison of a nanowire array with a single nanowire shows that the current density (J(SC)) is preserved for a range of nanowire morphologies. The J(SC) of a nanowire array depends on the spacing of its consti

We report on the optimization of the optical and electrical properties of IGZO/Ag/IGZO multilayer films as a function of IGZO thickness. The transmission window slightly widened and shifted toward lower energies with increasing IGZO thickness. The IGZO(39 nm)/Ag(19 nm)/IGZO(39 nm) showed transmittance 88.7% at 520 nm. The optical transmittance spectra were examined by finite-difference time-domain (FDTD) simulations. The carrier concentration decreased from 1.73 × 1022 to 4.99 × 1021 cm-3 with i

We designed a near-unity transmittance dielectric/Ag/ITO electrode for high-efficiency GaN-based lightemitting diodes by using the scattering matrix method. The transmittance of an ultrathin metal layer, sandwiched between a dielectric layer and an ITO layer, was investigated as a function of the thickness and the optical constant of each constituent layer. Three different metals (Ag, Au, and Al) were examined as the metal layer. The analytical simulation indicated that the transmittance of a di

We study various morphological effects due to optical cavities that are formed into metal substrates for the implementation of frequency-selective black absorbers. The absorption spectra (l ¼ 500e3000 nm) of patterned metal substrates are investigated by conducting full-vectorial electromagnetic simulations. The diameter of optical cavities determines a cut-off wavelength at which absorption begins to drop off exponentially. The cut-off wavelength is gradually redshifted by increasing the diamet

We studied morphological designs for enhanced light extraction from deep-ultraviolet AlGaNflip-chip light-emitting diodes with an absorptive p-type GaN layer. Ray tracing simulations wereperformed to investigate the dependence of the extraction efficiency on the thickness of the sapphiresubstrate, the diameter of mesa columns within arrays, and the refractive index of the cladding layerbetween the multiple quantum wells and the p-type GaN. The extraction efficiency was significantlyimproved, com

A vertical light-emitting diode (LED) with a chip size of 500 × 500 µm2 was fabricated by the laser lift-off (LLO) process of an InGaN-based blue LED wafer. After the LLO process, photonic crystal patterns by UV nano-imprint lithography were formed on the n-GaN top layer of the vertical LED over the entire area with a diameter of 2 inches. As the result of n-GaN patterning, light output power of the vertical LED with photonic crystals was increased by up to 44% compared to that of the vertical L

We study design principles to boost the extraction of light from core/shell GaN nanowire optical emitters. A full-vectorial electromagnetic simulation reveals that the extraction efficiency of an emitter within a nanowire cavity depends strongly on its position; the efficiency becomes maximized as the emitter’s location approaches the center of the structure. The total extraction of light is sinusoidally modulated by the nanowire diameter, which is directly correlated with optical resonances. Th

We studied broadband light absorption in laterally oriented single Si nanowires placed on metallic and dielectric substrates. Finite-difference time-domain simulation showed that when a Ag bottom mirror was adjacent to a Si nanowire, the optical resonances were significantly amplified at every resonant wavelength beyond the classical limit given by ray optics, thereby significantly enhancing the absorption efficiency. In particular, an omnidirectional Ag mirror was effective for sustaining two-d

Modern photovoltaics (PVs) are increasingly designed to be thinner and more transparent, thus enabling seamless integration into buildings and vehicles in urban environments. However, semitransparent thin-film PVs face inherent challenges in sunlight capture due to the limited volume of absorbing materials and the absence of efficient light-trapping strategies. Herein, we report a geometric design for light trapping in thinfilm PVs using a wedge-shaped microprism sheet. This microprism sheet, at

We studied external and internal patterns for boosting light extraction from GaN light-emittingdiodes (LEDs). With a transparent conductive layer (TCL) inserted between an external patternand an upper GaN plane, light extraction increased in a thin, high-refractive-index TCL. A periodicarray of air voids embedded in a GaN medium yielded an extraction efficiency similar to the externalpattern’s one. For double-layer patterns, as the internal pattern was close to multiple quantum wellswithin a wav

We develop and optimize thin anti-reflection coatings (ARCs) for highly anisotropic materials in the mid infrared. Unlike conventional ARCs that assume nearly isotropic refractive indices, this work fully integrates the anisotropic nature of materials into the design process. We describe two designs of thin ARCs for highly anisotropic materials: a single form-birefringent layer, and a planar bilayer. We realized the planar bilayer ARC experimentally, demonstrating excellent mid-infrared anti-ref