Hyun-Taek Lee

Carrier dynamics and activation energy of CdTe quantum dots in a CdxZn1−xTe quantum well

We investigate the optical properties of CdTe quantum dots (QDs) in a Cd0.3Zn0.7Te quantum well (QW) grown on GaAs (100) substrates. Carrier dynamics of CdTe/ZnTe QDs and quantum dots-in-a-well (DWELL) structure is studied using time-resolved photoluminescence (PL) measurements, which show the longer exciton lifetime of the DWELL structure. The activation energy of the electrons confined in the DWELL structure, as obtained from the temperature-dependent PL spectra, was also higher than that of electrons confined in the CdTe/ZnTe QDs. This behavior is attributed to the better capture of carriers into QDs within the surrounding QW.

Effects of two-dimensional electron gas on the optical properties of InAs/GaAs quantum dots in modulation-doped heterostructures

The Shubnikov–de Haas data showed that the carrier density of two-dimensional electron gas (2DEG) in the GaAs active region containing InAs quantum dot (QD) arrays embedded between modulation-doped Al0.25Ga0.75As/GaAs heterostructures increased with increasing doping concentration in the modulation layer. The transmission electron microscopy images showed that the sizes of the self-assembled InAs vertically stacked QD arrays inserted in the GaAs did not change significantly with increasing carrier density of the 2DEG. The photoluminescence (PL) spectra showed that the peaks corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole subband of the InAs QDs shifted to the higher energy side with increasing density of the 2DEG and that the full width at half maximum of the PL spectrum increased slightly with increasing density of the 2DEG.

Existence and atomic arrangement of microtwins in hexagonal MnAs ferromagnetic epilayers grown on GaAs (100) substrates with monolayer InAs Buffers

Selected-area electron-diffraction pattern (SADP) and high-resolution transmission electron microscopy (HRTEM) measurements were carried out to investigate the existence and the atomic arrangement of microtwins in hexagonal MnAs ferromagnetic epilayers grown on GaAs (100) substrates with monolayer InAs buffer layers by using molecular beam epitaxy. The magnetization curve as a function of the magnetic field at 5 K showed that the MnAs thin films were ferromagnetic, and the magnetization curve as a function of the temperature revealed that the ferromagnetic transition temperature was as high as 325 K. The SADP and HRTEM results showed that an epitaxial relationship was formed among the hexagonal MnAs layer, the InAs layer, and the zincblende GaAs substrate. Microtwins existed between the MnAs grain boundaries on top of the InAs layers. Based on the SADP and HRTEM results, we present a possible atomic arrangement of the microtwins for the MnAs-InAs-GaAs heterostructure.

Landscape Assessment and Improvement of the View Area by Selecting the Landscape Control Point

The purpose of this study is to quantitatively measure the view target and the view area through the selection of landscape control point by selecting Jimyeong-dong Dong-gu and Yeongyeong-dong Buk-gu Daegu, which are planned as the large scale housing complex development area, as the target places. It is very meaningful that from the simulation based on this measurement, the improvement methods are attempted to be suggested at the project level. The results of this study are as follows. First, the total number of viewing targets derived from the literature analysis for the selection of the viewing targets was 24, and finally derived main viewing targets were 4 places. Second, the total number of selection criteria of the derived landscape control point was 15, and these were re-categorized as prospect, accessibility and publicness according to the common property. The preliminary LCPs were selected by measuring the publicness and accessibility, and because of the said measurement, a total of 43 preliminary LCPs were selected. The final LCPs were selected by estimating the prospect of the selected preliminary LCPs, and as a result of estimation, a total of 29 final LCPs were selected. Finally, the total number of evaluation indicators derived from literature analysis was 26. Because of the valuation by the landscape control point, it was found that the 2 view areas were the I grade, 3 areas were II grade and 3 areas were the V grade, the lowest grade among 29 view areas. From the analysis on problems for the improvement methods, 4 improvement-indicators including the diversity of land mosaic were selected for the view area-1 without considering the development project drawing. In addition, for the view area-2 with considering the development project drawing, the landscape as the scenery forests was well formed, and the arrangement of architectures for the security of view corridor was right angle arrangement, and their floor number was 10.

Influence of the Natural Forest Service Quality on User`s Satisfaction and Demand for Revisit - By Focusing on Five Natural Forest in Kyung-buk Province -

The purpose of this research is to practically figure out the relationship between Natural Forest service quality on user`s satisfaction and demand to revisit. The results are as follows: First, the agent service quality, facility, accessibility, and cost as factors of the Natural Forest service quality. These are all influenced positively for visitor`s satisfaction by priority of agent service> accessibility> facility> cost. Second, the agent service quality, facility, accessibility are all influenced positively on visitor`s demand on revisit by priority of agent service> accessibility> facility. But the cost doesn`t make an influence on revisiting. Third, the visitor`s satisfaction made it as an influence on revisiting demand positively. These are the results for the research m service quality, user`s satisfaction, facility, accessibility, and cost of the 5 Natural Forest over the Kyung-buk Province. We finally figured out the agent service quality is the most important factor to improve the quality of Natural Forest facility. We are sure about the improvement of the agent service quality which will make it successful.

Classification of Landscape Type on Land and Evaluation of Site-suitability Based on It

The purpose of this study is to find ways of evaluating the suitability of sites being considered for development of different types of parks in the vicinity of yangmock-myun kyoung buk, where a large project(as large as about14.0) has been planned. The results are as follows. Three surveys for selecting the assessment indicators were performed. The first survey analyzed the importance of 23 selected assessment indicators based on a review of existing literature review and an on-the-spot research. The second survey selected assessment indicators for each park type. The third survey computed additive values of selected assessment indicators by the park types. It used a method of standardizing the average importance of indicators by making their sum equal to 10. These additive values were then multiplied by each grade of indicators to make a final evaluation. An evaluation of the site-suitability of park types was performed twice. The purpose of the first evaluation was to figure out how much each type met the minimum requirements targeted for all landscape types. The minimum requirements were derived by using a relative comparison between the standard of value rating of the assessment indicators, which was over the medium magnitude on the importance analysis, and the result of field research. A second evaluation estimated the targeted sites that met the minimum requirements. Value ratings of second assessment indicators were quantitatively divided as 1 to 3 grade and the evaluation scores were added, giving an additive value for each assessment indicator. The evaluation score on each park type was rated on a scale of 1 to 3 according to their averages, (from lowest to highest). Since this evaluation model of the site suitability on park types only focused on the `face` of space in this study, additional analysis is necessary for setting the evaluation model and incorporating the overall impact of space, network connection and other factors, considering `spot`, `line` and `face` aspects of space.

Formation mechanisms of self-assembled ZnSe nanostructures on Cl-doped ZnSe thin films grown on (100) GaAs substrates

Bright-field transmission electron microscopy images, high-resolution transmission electron microscopy images, energy dispersive spectroscopy profiles, and high-resolution x-ray diffraction curves showed that a high density of ZnSe nanostructures with a small size was formed on the Cl-doped ZnSe thin films grown on GaAs substrates. The formation of the ZnSe nanostructures was attributed to the strain energy resulting from the existence of the compressive strain generated by the accumulation of Cl impurities on the surface of the ZnSe thin film and from the residual strain existing in the ZnSe thin film with a thin thickness.