Jun Oh 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.

Short wavelength infrared photodetector and light emitting diode based on InGaAsSb

We report on InGaAsSb infrared photodetector and light emitting diode for short wavelength infrared detection and emission. The InGaAsSb samples were grown by molecular beam epitaxy (MBE) system on a GaSb substrate. In order to investigate the structural properties of InGaAsSb layer, we took a high resolution XRD and low voltage SEM. The InGaAsSb devices were processed in 400×400 μm2 using inductively coupled plasma etching. We have measured the spectral response of InGaAsSb based photodetector using various temperature and bias. The cut-off wavelength of photodetector was 3.0 μm at room temperature. We also report an electroluminescence of InGaAsSb LED. Keywords: Short wavelength infrared, photodetector, light emitting diode, InGaAsSb, GaSb.

Formation of GeO2 complex composed nanostructures by the vapor liquid solid method

In this work, we presented the synthesized results of GeO2 complex composed nanostructures (nanobubbles (NBs) on sidewall of nanowires (NWs)) via the vapor liquid solid (VLS) method. By using a 20xa0nm of Au nano–film (AuNF) catalyst, prepared by the conventional direct current (DC) magnetron sputtering deposition method, the GeO2 NBs were randomly synthesized along the sidewall of GeO2 NW based two thermal annealing modes in vacuum–furnaces (~10−3 torr) with the diameter in the region conformed from 150 to 450xa0nm. Transmission electron microscopy (TEM) images indicated the different crystalline phases of NB depended on annealing temperature (T2u2009=u2009600 and 650u2009°C for (102) & (110) plane, respectively). Energy–dispersive x–ray (EDX) analysis results only showed oxygen (69.08%) and germanium (30.92%) of GeO2 nanobubble. Also, bright blue emission peak at wavelength of 438xa0nm was observed from GeO2 NB–NW–like structure at room temperature. This leads to applications of optoelectronic nanodevices. The detailed of NBs formation mechanism on NW was also discussed.

A THz plasmonic perfect absorber and Fabry-Perot cavity mechanism

The plasmonic metamaterial perfect absorber (MPA) is a recently developed branch of metamaterial which exhibits nearly unity absorption within certain frequency range. The optically thin MPA possesses characteristic features of angular-independence, high Q-factor and strong field localization that have inspired a wide range of applications including electromagnetic wave absorption, spatial and spectral modulation of light, selective thermal emission, thermal detecting and refractive index sensing for gas and liquid targets. In this work, we demonstrate a MPA working at terahertz (THz) regime and characterize it using an ultrafast THz time-domain spectroscopy (THz-TDS). Our study reveal an ultra-thin Fabry-Perot cavity mechanism compared to the impedance matching mechanism widely adopted in previous study. Our results also shows higher-order resonances when the cavities length increases. These higher order modes exhibits much larger Q-factor that can benefit potential sensing and imaging applications.

A multilayer effective medium model for plasmonic perfect absorber

The plasmonic metamaterial perfect absorber (MPA) is a recently developed branch of metamaterial which exhibits nearly unity absorption within certain frequency range [1-6]. The optically thin MPA possesses characteristic features of angular-independence, high Q-factor and strong field localization that have inspired a wide range of applications including electromagnetic wave absorption [3, 7, 8], spatial [6] and spectral [5] modulation of light [9], selective thermal emission [9], thermal detecting [10] and refractive index sensing for gas [11] and liquid [12, 13] targets. In this work, we demonstrate a MPA can be understood by a multiple layer medium model. Using a transfer matrix method, we are able to reproduce the overall reflection of MPA using effective permittivity and effective permeability of each layers. Our study reveal an ultrathin Fabry-Perot cavity mechanism compared to the impedance matching mechanism widely adopted in previous study [1-6].

Long wavelength infrared photodetector using submonolayer quantum dots

We report on InAs SML QD infrared photodetector performance for long wavelength infrared detection. The device structure consists of InAs SML QDs embedded in InxGa1-xAs quantum well (QW) surrounded by GaAs and AlxGa1- xAs barrier. In order to investigate the structural properties of SML QDs, we took cross-sectional STEM images. We have measured the polarization dependent spectral response of SML-QD based photodetector using various angular inplane and out-plane polarizations. We also report a systematic approach for controlling the intersubband transition energy level in SML QD infrared photodetectors, in order to control the peak wavelength of the device.

Investigation of the shape of submonolayer quantum dots using a polarization-dependent photocurrent

Structural and optical characterization of multi-stack InAs/InGaAs submonolayer quantum dots (SML-QDs) grown under the Stranski–Krastanov growth mode was performed via a polarization-dependent study. Various angular in-plane (plane perpendicular to growth direction) and out-of-plane (plane parallel to the 45°-polished facet) polarization-dependent spectral photocurrents were measured to investigate the three-dimensional quantum confinement in multi-stack 0.3 monolayer InAs SML-QDs (the shape of SML-QDs embedded in an SML-QD based photodetector). Scanning transmission electron microscopy images revealed the interdiffusion of indium atoms between SML-QDs and the InGaAs quantum well due to an insufficient amount of indium, which agrees well with the tendency of s- to z-polarized response ratios.