Young-Ho Ko

Electronics and Telecommunications Research Institute | ETRI · Department of Photonic/Wireless Convergence Components Researcht

Electrically driven quantum dot, wire, and well hybrid light-emitting diodes are demonstrated by using nanometer-sized pyramid structures of GaN. InGaN quantum dots, wires, and wells are formed at the tops, edges, and sidewalls of pyramids, respectively. The hybrid light-emitting diodes containing low-dimensional quantum structures are good candida...

Broadband visible light emitting, three-dimensional hexagonal annular microstructures with InGaN/GaN multiple quantum wells (MQWs) are fabricated via selective-area epitaxial growth. The single hexagonal annular structure is composed of not only polar facet of (0001) on top surface but also semi-polar facets of {10-11} and {11-22} in inner and oute...

A key issue in a single photon source is fast and efficient generation of a single photon flux with high light extraction efficiency. Significant progress toward high-efficiency single photon sources has been demonstrated by semiconductor quantum dots, especially using narrow bandgap materials. Meanwhile, there are many obstacles, which restrict th...

Significance Control and optimization of interaction between light and single quantum emitters are a crucial issue for cavity quantum electrodynamics studies and quantum information science. Although considerable efforts have been made, reliable and reproducible coupling between quantum emitter and cavity mode still remains a grand challenge due to...

We fabricated the InGaN double-hetero structure (DHS) on the nano-sized pyramid structure and successfully demonstrated efficient red color emission at 650 nm from this unique structure. The nano-sized pyramid structure was fabricated by selective area growth method with nano-imprint. The diffusion length of composite atoms and compositional pullin...

GaAs-on-Si templates with two different dislocation filter layers (DFLs) were grown at 550 °C low-temperature (LT)-DFL and 660 °C high-temperature (HT)-DFL using metal organic vapor-phase epitaxy and the effects of the growth temperature were studied. The threading dislocation density (TDD) values of LT-DFL and HT-DFL were 5.2 × 10 ⁷ cm ⁻² and 1.5...

Among the diverse platforms of quantum light sources, epitaxially grown semiconductor quantum dots (QDs) are one of the most attractive workhorses for realizing various quantum photonic technologies owing to their outstanding brightness and scalability. There exist various material systems for these QDs based on their appropriate emission bandwidth...

GaAs-on-Si templates with two different dislocation filter layers (DFLs) were grown at 550 °C low temperature (LT)-DFL and 660 °C high temperature (HT)-DFL using metal organic vapour-phase epitaxy and the effects of the growth temperature were studied. The threading dislocation density (TDD) values of LT-DFL and HT-DFL were 5.2 × 10 ⁷ cm ⁻² and 1.5...

Incorporating solid‐state quantum emitters into optical fiber networks enables the long‐distance transmission of quantum information and the remote connection of distributed quantum nodes. However, interfacing quantum emitters with fiber optics encounters several challenges, including low coupling efficiency and delicate configuration. In this stud...

Incorporating solid-state quantum emitters into optical fiber networks enables the long-distance transmission of quantum information and the remote connection of distributed quantum nodes. However, interfacing quantum emitters with fiber optics encounters several challenges, including low coupling efficiency and stability. Here, we demonstrate a hi...

The heterogeneous integrated quantum dot with piezoelectric material was fabricated for wavelength tunable quantum emitters. The integrated structure effectively generated local strain with applying voltage, resulting in wavelength tunable single photon emission and adjusting fine-structure splitting for entangle photon pair generation.

We demonstrate efficient fiber-interfacing photonic devices based on hole gratings producing a narrow directional beam that directly launch single photons from quantum dots into a standard single-mode fiber by matching the numerical aperture.

GaAs on Si grown via metalorganic chemical vapor deposition is demonstrated using various Si substrate thicknesses and three types of dislocation filter layers (DFLs). The bowing was used to measure wafer-scale characteristics. The surface morphology and electron channeling contrast imaging (ECCI) were used to analyze the material quality of GaAs f...

One of the challenging issues in free-space quantum key distribution (QKD) is the requirement of active compensation of the reference frame between the transmitter and receiver. Reference frame independent (RFI) QKD removes active compensation, but it requires more quantum states. A recent proposal can effectively reduce the required quantum states...

A GaAs quantum-well laser diode was directly grown on silicon (001) substrate by a hybrid technique comprising AlAs nucleation and thermal cycle annealing. The hybrid technique provided the advantages of superior surface roughness, high quantum efficiency, and low threading dislocation density (TDD) of a thin buffer. The TDD was quantitatively char...

In the distribution of quantum states over a long distance, not only are quantum states corrupted by interactions with an environment but also a measurement setting should be re-aligned such that detection events can be ensured for the resulting states. In this work, we present measurement-protected quantum key distribution where a measurement is p...

High quality GaAs was epitaxially grown on silicon(001) substrate through a hybrid technique of metalorganic chemical vapor deposition. The hybrid technique was comprised of AlAs nucleation and thermal cycle annealing to take advantages of both methods. The AlAs nucleation improved the surface roughness of GaAs buffer and the thermal cycle annealin...

We present a cost-effective and bandwidth-enhanced 64-Gbaud micro-intradyne coherent receiver based on hybrid integration of InP waveguide-photodetector (WG-PD) and silica planar lightwave circuit (PLC). InP waveguide-photodetector (WG-PD) arrays are simply chip-to-chip bonded and optically butt-coupled to a silica-based dual-polarization optical h...

We report on a low-cost hybrid-integrated Micro-ICR based on a silica DP-OH and InP WG-PDs. RF and DC FPCB wirings provide low-cost and good RF performance. A 3-dB bandwidth is measured to be ~36 GHz.

Beyond epitaxially grown planar-thin film structures, nanostructure-based group III-nitride materials have attracted intensive interest for light-emitting device applications. Nanostructures have distinctive optical and structural properties such as improved light extraction, fast spontaneous emission rate, large surface area, high crystal quality,...

We present a cost-effective dual polarization quadrature phase-shift coherent receiver module using a silica planar lightwave circuit (PLC) hybrid assembly. Two polarization beam splitters and two 90? optical hybrids are monolithically integrated in one silica PLC chip with an index contrast of 2%-Δ. Two four-channel spot-size converter integrated...

We demonstrated the waveguide photodetector (WG PD) integrated with spot-size converter (SSC) for coherent receiver of 100Gb/s operation. The WG PD integrated with SSC was designed as diluted WG, dual lateral taper structure, and PIN-photodiode. The epitaxial layers of InxGa1-xAsyP1-y/InP, InxGa1-xAsyP1-y, and InGaAs were adopted as the diluted WG,...

White light-emitting diodes (LEDs) are becoming an alternative general light source, with huge energy savings compared to conventional lighting. However, white LEDs using phosphor(s) suffer from unavoidable Stokes energy converting losses, higher manufacturing cost, and reduced thermal stability. Here, we demonstrate electrically driven, phosphor-f...

For optimization of the waveguide in an InGaN/GaN/AlGaN laser diode (LD) on a sapphire substrate, we solved the wave equation of the InGaN/GaN/AlGaN waveguide. Several guided modes in the LD waveguide have been presented and we have shown that an anti-crossing effect between the guided modes is an important phenomenon to understand the complicated...

Waveguide photodetector was fabricated for high responsivity and low PDL when butt-coupled with 2%-Δ planar lightwave circuit devices. Optimizing the thicknesses of tapers in spot-size converter, fabricated device showed responsivity of 0.72 A/W and PDL of 0.11dB.

We present group III-nitride semiconductor nanostructures grown on various types of GaN-based pyramid, annular, columnar, and tapered structures, together with their applications in broadband light emitting devices, unidirectional photonic diodes, and single photon sources.

White light emitting InGaN nanostructures hold a key position in the future solid-state lighting applications. Although many suggestive approaches to form group III-nitride vertical structures have been reported, more practical and cost effective methods are still needed. Here, we present a new approach for GaN/InGaN core-shell nanostructures on a...

Multi-color and broadband visible emission was realized thorough the hexagonal annular structure of GaN. The annular structure fabricated by selective-area growth emitted purple, blue and green color-emission from the multi-facets. The hexagonal annular structure provided various sidewalls of {101} and {112} semi-polar facets, and (0001) polar face...

We propose a method to quantitatively analyze the internal quantum efficiency (IQE) as well as the efficiencies of non-radiative recombination in the active region (NRA) and carrier escape out of the active region (ESC) by comparing open-circuit (OC) to short-circuit (SC) conditions of InGaN-based light-emitting diodes (LEDs). First, the IQE was ex...

Supplementary information

We report the formation mechanism and the characteristics of catalyst-free and mask-free heteroepitaxial GaN submicrometer- and micrometer-sized rods (SMRs) under biaxial strain grown on Si(111) substrates by metal-organic chemical vapor deposition. We found that the GaN SMRs on Si(111) substrates were subject to strong tensile strain on their N-te...

A dislocation-eliminating chemical control method for high-quality GaN nanostructures together with various types of InGaN quantum well structures are demonstrated using a chemical vapor-phase etching technique. Unlike chemical wet etching, chemical vapor-phase etching could efficiently control the GaN and form various shapes of dislocation-free an...

We have developed and demonstrated an effective method for fabricating the moth eye structures formed by charged nanoparticle lithography (cNPL). We attached high-density gold nanoparticles (Au NPs) to GaN without aggregation by making the surface of Au NPs negatively charged and GaN positively charged. Au NPs were effectively used as an etching ma...