Hyunseok Kim

Three-stage nucleation and growth of Ge self-assembled quantum dots grown on partially relaxed SiGe buffer layers

We investigate the magnetic field inversion symmetry of the pumped currents in quantum pumps with various discrete symmetries using Floquet scattering matrix approach. We found the pumped currents can have symmetries

Monolithically Integrated InGaAs Nanowires on 3D Structured Silicon-on-Insulator as a New Platform for Full Optical Links

I(B,phi) = -I(-B,-phi)

Influence of the wetting-layer growth kinetics on the size and shape of Ge self-assembled quantum dots on Si(001)

and

Influence of a buried misfit dislocation network on the pyramid-to-dome transition size of Ge self-assembled quantum dots on Si(001)

I(B,phi) = I(-B,-phi)

Monolithic InGaAs Nanowire Array Lasers on Silicon-on-Insulator Operating at Room Temperature

, where

Improved room-temperature luminescence of core-shell InGaAs/GaAs nanopillars via lattice-matched passivation

phi

Nanopillar array band-edge laser cavities on silicon-on-insulator for monolithic integrated light sources

is the phase difference of two time dependent perturbations, depending on the discrete symmetry considered. The results in the adiabatic limit for each discrete symmetry are compared with those of Brouwers formula.

Telecom-Wavelength Bottom-up Nanobeam Lasers on Silicon-on-Insulator

Monolithically integrated III-V semiconductors on a silicon-on-insulator (SOI) platform can be used as a building block for energy-efficient on-chip optical links. Epitaxial growth of III-V semiconductors on silicon, however, has been challenged by the large mismatches in lattice constants and thermal expansion coefficients between epitaxial layers and silicon substrates. Here, we demonstrate for the first time the monolithic integration of InGaAs nanowires on the SOI platform and its feasibility for photonics and optoelectronic applications. InGaAs nanowires are grown not only on a planar SOI layer but also on a 3D structured SOI layer by catalyst-free metal-organic chemical vapor deposition. The precise positioning of nanowires on 3D structures, including waveguides and gratings, reveals the versatility and practicality of the proposed platform. Photoluminescence measurements exhibit that the composition of ternary InGaAs nanowires grown on the SOI layer has wide tunability covering all telecommunication wavelengths from 1.2 to 1.8 μm. We also show that the emission from an optically pumped single nanowire is effectively coupled and transmitted through an SOI waveguide, explicitly showing that this work lays the foundation for a new platform toward energy-efficient optical links.

On the formation mechanism of epitaxial Ge islands on partially relaxed SiGe buffer layers

The growth temperature of the wetting layer is used as the key variable in the study of a series of Ge self-assembled quantum dots on Si(001) substrates. A relaxed SiGe buffer layer is used for most of the samples as a means of maintaining the density of Ge dots. Ge dots are in the shapes of pyramids, domes, and superdomes, similar to those reported in the literature. A significant difference in the fraction of pyramids is observed between samples with wetting layers grown at low (280u200a°C) and high (650u200a°C) temperatures. This difference is in turn dependent on the total amount of Ge deposited or equivalently, the average size of dots. These observations point to the presence of Si during the initial stage of Ge dot formation and that the fraction of pyramids as well as the critical size for the transition from pyramids to domes are influenced by the presence of Si.

Enhanced interlayer neutral excitons and trions in trilayer van der Waals heterostructures

The critical sizes of the pyramid-to-dome transition of Ge self-assembled quantum dots (SAQDs) grown on relaxed SiGe buffer layers were investigated for the relationship between the misfit strain built in dots and nucleation sites. The strain field of arrays of buried dislocations in a relaxed SiGe buffer layer provided preferential nucleation sites for quantum dots. Burgers vector analysis using plan-view transmission electron microscopy verified that the preferential nucleation sites of Ge SAQDs depended on the Burgers vector direction of corresponding dislocations. The measurement of the lateral distance between SAQDs and dislocations clarified that the location of SAQDs was at the intersection of the dislocation slip plane and the top surface. The samples are fabricated to contain low dislocation densities. The average dislocation spacing is larger than the surface migration length of Ge adatoms, resulting in two groups of SAQDs, those that are located along the dislocations, and those that are not. Atomic force microscopy observations showed a distinctively larger critical size for Ge SAQDs grown over the intersection of the dislocation slip plane and the top surface than those grown in regions between dislocations. These experimental observations indicate that the critical size of the pyramid-to-dome transition is strongly dependent on misfit strain in SAQDs with lower strain being associated with a larger critical size.