Deok-kee Kim

Enhanced transmission due to antireflection coating layer at surface plasmon resonance wavelengths

We present experiments and analysis on enhanced transmission due to dielectric layer deposited on a metal film perforated with two-dimensional periodic array of subwavelength holes. The Si3N4 overlayer is applied on the perforated gold film (PGF) fabricated on GaAs substrate in order to boost the transmission of light at the surface plasmon polariton (SPP) resonance wavelengths in the mid- and long-wave IR regions, which is used as the antireflection (AR) coating layer between two dissimilar media (air and PGF/GaAs). It is experimentally shown that the transmission through the perforated gold film with 1.8 µm (2.0 µm) pitch at the first-order (second-order) SPP resonance wavelengths can be increased up to 83% (110%) by using a 750 nm (550 nm) thick Si3N4 layer. The SPP resonance leads to a dispersive resonant effective permeability (μeff ≠ 1) and thereby the refractive index matching condition for the conventional AR coating on the surface of a dielectric material cannot be applied to the resonant PGF structure. We develop and demonstrate the concept of AR condition based on the effective parameters of PGF. In addition, the maximum transmission (zero reflection) condition is analyzed numerically by using a three-layer model and a transfer matrix method is employed to determine the total reflection and transmission. The numerically calculated total reflection agrees very well with the reflection obtained by 3D full electromagnetic simulations of the entire structure. Destructive interference conditions for amplitude and phase to get zero reflection are well satisfied.

Effects of H2 plasma and annealing on atomic-layer-deposited Al2O3 films and Al/Al2O3/Si structures

We evaluated the effects of H2 plasma and thermal treatment on current–voltage (I–V) and capacitance–voltage (C–V) characteristics using Al/Al2O3/Si. H2 plasma treatment reduced the concentration of C and enhanced the diffusion of Si and O atoms and the mean breakdown field strength. The breakdown field increased significantly after rapid thermal annealing (RTA) due to crystallization and the formation of an interface layer between Si and Al2O3, which was confirmed by TEM, secondary ion mass spectroscopy (SIMS), and three-dimensional (3D) atom probe tomography. H2 plasma treatment produced a negative fixed charge due to the outgassing of C and H2, and RTA produced a positive fixed charge.

A Low-loss Metasurface Antireflection Coating on Dispersive Surface Plasmon Structure

Over the years, there has been increasing interest in the integration of metal hole array (MHA) with optoelectronic devices, as a result of enhanced coupling of incident light into the active layer of devices via surface plasmon polariton (SPP) resonances. However, not all incident light contributes to the SPP resonances due to significant reflection loss at the interface between incident medium and MHA. Conventional thin-film antireflection (AR) coating typically does not work well due to non-existing material satisfying the AR condition with strong dispersion of MHA’s effective impedances. We demonstrate a single-layer metasurface AR coating that completely eliminates the refection and significantly increases the transmission at the SPP resonances. Operating at off-resonance wavelengths, the metasurface exhibits extremely low loss and does not show resonant coupling with the MHA layer. The SPP resonance wavelengths of MHA layer are unaffected whereas the surface wave is significantly increased, thereby paving the way for improved performance of optoelectronic devices. With an improved retrieval method, the metasurface is proved to exhibit a high effective permittivity () and extremely low loss (tan δ ~ 0.005). A classical thin-film AR coating mechanism is identified through analytical derivations and numerical simulations.

Electrical characteristics and step coverage of ZrO2 films deposited by atomic layer deposition for through-silicon via and metal–insulator–metal applications

The electrical characteristics and step coverage of ZrO2 films deposited by atomic layer deposition were investigated for through-silicon via (TSV) and metal–insulator–metal applications at temperatures below 300 °C. ZrO2 films were able to be conformally deposited on the scallops of 50-µm-diameter, 100-µm-deep TSV holes. The mean breakdown field of 30-nm-thick ZrO2 films on 30-nm-thick Ta(N) increased about 41% (from 2.7 to 3.8 MV/cm) upon H2 plasma treatment. With the plasma treatment, the breakdown field of the film increased and the temperature coefficient of capacitance decreased significantly, probably as a result of the decreased carbon concentration in the film.

Transition of Resistive Switching to Bidirectional Diode in Cu2O/Cu Nanowires

Cu2O/Cu nanowires of about 2 µm length were electrodeposited within anodized aluminum oxide templates in an aqueous acidic solution using template-assisted pulse-reverse electrolysis. In the virgin state, reversible copper filaments were formed by using the copper ions driven by an electric field towards the cathode. Initially, the resistive switching dominated the electrical characteristics of the Cu2O/Cu nanowires due to the low-resistance reversible copper filaments. After the permanent breakup of the copper filaments under the high current density, the Cu2O/Cu nanowire showed bipolar exponential characteristics, which was attributed to mixed ionic and electronic conduction.

Low Temperature Synthesis and Properties of BiFeO3

Extensive efforts have been made to synthesize single phase and stoichiometric BiFeO3. Some modified techniques have been tried in synthesizing BiFeO3 as compared with the conventionally used co-precipitation method. Thermogravimetric Analysis/Differential Scanning Calorimetry and x-ray diffraction experiments were used exclusively to explore the effects of heat treatment temperature and time on crystallographic behavior of the prepared BiFeO3 powder. Field emission scanning electron microscopy was used to explore the microstructure of the synthesized BiFeO3. The appearance of different magnetic phases in 57Fe Mössbauer spectra and field dependent magnetization was confirmed on the basis of particle size distribution. In this research, an easy, low cost and high-yield method for the low temperature single phase and stoichiometric synthesis of BiFeO3 has been suggested.

Theoretical study of potential performance of armchair graphene nanoribbon field effect transistors: Dependence on channel dimensions and contact resistance

In this paper, we examine the performance limitations of graphene nanoribbon field effect transistors (GNRFETs) with various channel dimensions and electrode contact resistances. To do this, we formulate a self-consistent non-equilibrium Greens function method in conjunction with the Poisson equation. We model the behavior of GNRFETs with nanometer dimensions and relatively large bandgaps operating as metal–oxide–semiconductor field effect transistors (MOSFETs) and calculate their performance including contact resistance effects typically occurring at the graphene nanoribbon (GNR) channel and electrodes. We propose a metric for GNRFETs to compete with the current silicon CMOS high performance or low power devices and explain that this can vary significantly depending on the contact resistance.

Impact of graphene–graphite films on electrical properties of Al2O3 metal–insulator–semiconductor structure

The diffusion barrier property of directly grown graphene–graphite films between Al2O3 films and Si substrates was evaluated using metal–insulator–semiconductor (MIS) structures. The roughness, morphology, sheet resistance, Raman spectrum, chemical composition, and breakdown field strength of the films were investigated after rapid thermal annealing. About 2.5-nm-thick graphene–graphite films effectively blocked the formation of the interfacial layer between Al2O3 films and Si, which was confirmed by the decreased breakdown field strength of graphene–graphite film structures. After annealing at 975 °C for 90 s, the increase in the mean breakdown field strength of the structure with the ~2.5-nm-thick graphene–graphite film was about 91% (from 8.7 to 16.6 MV/cm), while that without the graphene–graphite film was about 187% (from 11.2 to 32.1 MV/cm). Si atom diffusion into Al2O3 films was reduced by applying the carbon-based diffusion barrier.