Il Ki Han

Electrical characterization of GaAs/AlGaAs multi-quantum wells for quantum cascade laser

In this study, we investigated the electrical properties of three QW active region by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements (Blood, 1992 and Kim, 2004). Then, the optical properties were measured also by photoluminescence (PL) and Fourier transformed infra-red spectroscopy (FTIR), etc. In this study, we prepared GaAs/AlGaAs single and three QWs samples grown on n-GaAs substrates as a simplified active region except for other complex regions of QCL device. Generally, the QCL structure has made up of 26th/spl sim/40th period of the injection/active region, but the structure is too complicated to analyze electrical properties. Thus, we used simple structure in this study. And then, in order to measure C-V and DLTS, a Schottky diode was made by Au-gate formation and indium ohmic contact below the backside.

Selective Epitaxy Growth of Multiple-Stacked InP/InGaAs on the Planar Type by Chemical Beam Epitaxy

Selective area epitaxy of multiple-stacked InP/InGaAs structures were grown by chemical beam epitaxy. The width of top of the multiple-stacked InP/InGaAs layer which were selectively grown on the stripe lines parallel to the direction was narrowed, while the width of top of the multiple-stacked InP/InGaAs layer on the stripe lines parallel to the was widen. This difference according to the and direction was explained by the growth of InGaAs A and B faces on the (100) InP surface on the stripe lines parallel to the direction. Under growth rate of , top of the multiple-stacked InP/InGaAs was flattened as the pressure of group V gas was decreased. This phenomenon was understood by the saturation of group V element on the surface.

Photolumineseence analysis of white-emitting si nanoparticles using effective mass approximation method

Commercial interests in white-light-emitting devices are growing, as is the need for nanophosphors based on semiconductor nanoparticles, in which changing the size distribution produces marked changes in color. Silicon, which is abundant, cheap, and nontoxic, is an ideal material for nanophosphors even though synthesis routes for 11-VI nanoparticles like CdSe are well established. Silicon nanoparticles (1 to 5 nm in diameter), with photoluminescence quantum efficiencies exceeding 20 %,1) could be useful as the emissive phosphor layer in solidstate light-emitting diodes (LEDs) for general illumination purposes. The small diameter of the nanoparticles, much smaller than the wavelength of visible light, might eliminate light scattering and associated optical losses.

Threshold Current Reduction of GaAs/AlGaAs Quantum Cascade Laser due to the Deep Mesa Structure

GaAs/AlGaAs based quantum cascade lasers were fabricated with two different types of i) the shallow mesa type which was etched up to above active region and ii) the deep mesa type which was etched through active region. While the threshold current density of shallow mesa type was , the one of deep mesa type was reduced drastically up to . Such lowered threshold current density at deep mesa type attributed to the reduction of current loss to the lateral directions.

Optical power enhancement of superluminescent diodes utilizing trench

J-shaped superluminescent diodes (SLD) utilizing trench structure have been fabricated on the multiple quantum dots epi-structure with its ground state energy wavelength of . It was observed that optical power was drastically increased up to 20 times in comparison with that of SLD without trench structure, The electroluminescence characteristics showed that the peak intensity of excited state was several ten times higher in the SLD with trench than without trench structure. It is explained that the optical power enhancement of J-shaped SLD with trench structure resulted from the drastic increase of peak intensity of excited state.

Formation of Al 0.3 Ga 0.7 As/GaAs Multiple Quantum Wells on Silicon Substrate with AlAs x Sb 1-x Step-graded Buffer

The step-graded buffer (SGB) layer was grown on the Silicon (Si) substrate to overcome lattice mismatch between Si substrate and /GaAs multiple quantum wells (MQWs). The value of root-mean-square (RMS) surface roughness for 5 nm-thick GaAs grown on step-graded buffer layer was ~1.7 nm. /GaAs MQWs with AlAs/GaAs short period superlattice (SPS) were formed on the /Si substrate. Photoluminescence (PL) peak at 10 K for the /GaAs MQW structure showed relatively low intensity at ~813 nm. The RMS surface roughness of the /GaAs MQW structure was ~42.9 nm. The crystal defects were observed on the cross-sectional transmission electron microscope (TEM) images of the /GaAs MQW structure. The decrease of PL intensity and increase of RMS surface roughness would be due to the formation of the crystal defects.

Ethical Issues in Nanomaterials Technology and Relevant Policy Recommendations

For sustainable and responsible development of nanomaterials technology, the establishment of ethical system for sound social acceptance of the technology as well as the development of the technology itself is necessary. In this paper, global efforts to identify and resolve the ethical issues regarding nanotechnology is reviewed, in particular the environmental, health and safety issues in nanomaterials, and the tools such as communication and engagement of stakeholders, regulations, certifications and workplace guidelines are scrutinized. Finally the policy recommendations for the establishment of ethical systems for safe usage of nanomaterials.

Junction Temperature of Quantum Dot Laser Diodes Depending on the Mesa Depth

Junction temperature of quantum dot laser diodes is investigated by utilizing forward voltage-temperature method. In the case of ridge type laser diodes with deep mesa the increasing rate of junction temperature to current is about 0.05 K/mA, while in the case of shallow mesa the increasing rate is about 0.07 K/mA. It is explained that the relatively low increasing rate in the deep mesa results from the heat expansion to the lateral direction of mesa.