• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.7
• /
• pp.51-57
• /
• 1995

The theoretical analysis for AlInAs/GaInAs resonant tunneling diodes (RTDs), which have shown the improved negative differential resistance (NDR) characteristics, has scarcely been made in comparison with AlGaAS/GaAs RTDs. In this paper, the static current-voltage relation of Al$_{0.48}In_{0.52}As/Ga_{0.47}In_{0.53}$As RTDs were numerically estimated by using a self-consistent method. Assuming a simplified RTD with single quantum well structure and spacer layers, the peak current density (J$_{P}$) and the peak-to-valley current ratio (PVCR) were analysed as the function of the thickness of the well, the barrier and the spacer layer, and temperature. As the results, the peak current density and the peak-to-valley current ratio indicated a reciprocal relation roughly in respect to the thicknesses of the well and the barrier, and it was theoretically predicted that it be not attainable to provide a high peak current desity (J$_{P}$) over 1${\times}10^{5}A/cm^{2}$ as well as the large peak-to-valley current ratio (PVCR) over 10 that were the the critical conditions for the practical use.

• Journal of the Korean Vacuum Society
• /
• v.10 no.1
• /
• pp.81-86
• /
• 2001

We have investigated surface photovoltage characteristics of InGaAs grown by metalorganic chemical vapor deposition (MOCVD) method on semi-insulating GaAs. The splitted SPV signals from the substrate and epilayer were observed. The band gap energy of InGaAs was about 1.376 eV, The In composition(x) was determined by Pan's composition formula. The photovoltage gradually decreases with increasing frequency. This is because the transfer of charge from the surface states reduces. From the temperature dependent SPV measurement, we obtained Varshni and temperature coefficients. In spectrum of etched sample at 300 K, the 'A' peak below $E_o(GaAs)$ is related with residual impurity during sample growth.

• Korean Journal of Crystallography
• /
• v.7 no.1
• /
• pp.64-72
• /
• 1996

Calculation of the amount of excess arsenic charge has been carried out for the single crystal growth of GaAs with 1-T HB(single temperature zone horizontal Bridgman) method which has no low temperature arsenic zone. Based upon the investigation of the thermochemical properties of the Ga and As system, a general equation for the excess dimension of the ampoule and temperature gradient of the furnace. From this result, a theoretical background of the 1-T HB method has been constructed for the single crystal growth of GaAs.

• Korean Journal of Optics and Photonics
• /
• v.8 no.3
• /
• pp.213-217
• /
• 1997

We have measured photoluminescence (PL) and time-resolved PL in doped-GaAs. As increasing doping concentration, the PL spectra of n-type GaAs shift to higher energies while the PL spectra of p-type GaAs shift to lower energies than the bandgap of the undoped GaAs. The contribution of the Burstein-Moss effect overrules the band-gap narrowing in n-type GaAs, contrary to p-type GaAs. The PL rise time and decay time become shorter as increasing doping concentration. The PL rise and decay time in doped-GaAs depend on the type of majority carriers and their concentrations, which imply that the carrier-carrier interaction plays an important role in the energy relaxation processes.

• Journal of Microbiology and Biotechnology
• /
• v.17 no.5
• /
• pp.769-773
• /
• 2007

With the aim to produce ascorbic acid-2-phosphate(AsA-2-P) from L-ascorbic acid(AsA, Vitamin C), nine bacteria conferring the ability to transform AsA to AsA-2-P were isolated from soil samples alongside known strains from culture collections. Most isolates were classified to the genus Brevundimonas by 16S phylogenetic analysis. Among them, Brevundimonas diminuta KACC 10306 was selected as the experimental strain because of its the highest productivity of AsA-2-P. The optimum set of conditions for the AsA-2-P production from AsA using resting cells as the source of the enzyme was also investigated. The optimum cultivation time was 16 h and the cell concentration was 120g/l(wet weight). The optimum concentrations of AsA and pyrophosphate were 550mM and 450mM, respectively. The most effective buffer was 50mM sodium formate. The optimum pH was 4.5 and temperature was $40^{\circ}C$. Under the above conditions, 27.5g/l of AsA-2-P was produced from AsA after 36 h of incubation, which corresponded to a 19.7% conversion efficiency based on the initial concentration of AsA.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.1
• /
• pp.12-17
• /
• 1998

The heteroepitaxial growth of InP and GaInAs on GaAs substrates has been studied by using a new combination of source materials: ethyldimethylindium (EDMIn) and trimethylgallium (TMGa) as group III sources, and tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) as group V sources. Device quality InP heteroepitaxial layers were obtained by using a two-step growth process under atmospheric pressure, involving a growth of an initial nucleation layer at low temperature followed by high temperature annealing and the deposition of epitaxial layer at a growth temperature. The continuity and thickness of nucleation layer were important parameters. The InP layers deposited at 500$^{\circ}$- 55$0^{\circ}C$ are all n-type, and the electron concentration decreases with decreasing TBP/EDMIn molar ratio. The excellent optical quality was revealed by the 4.4 K photoluminescence (PL) measurement with the full width at half maximum (FWHM) of 4.94 meV. Epitaxial Ga\ulcorner\ulcorner\ulcornerIn\ulcorner\ulcorner\ulcornerAs layers have been deposited on GaAs substrates at 500$^{\circ}$ - 55$0^{\circ}C$ by using InP buffer layers. The composition of GaInAs was determined by optical absorption measurements.

• Progress in Superconductivity
• /
• v.14 no.1
• /
• pp.11-16
• /
• 2012

Based on fully self-consistent dynamical mean field theory (DMFT) method, we investigate electronic structure and Fermi surface nesting property of LiFeAs and NaFeAs, focusing on the correlation effect of iron 3d orbital. For LiFeAs, good nesting property by density functional theory (DFT) method is much suppressed by DFT+DMFT method due to the orbital-dependent renormalization magnitude. NaFeAs shows a similar behavior, but a better nesting is obtained than LiFeAs from DFT+DMFT Fermi surfaces. Our result is consistent with the observed superconducting (spin density wave) ground state of LiFeAs (NaFeAs).

• Journal of the Korean Vacuum Society
• /
• v.12 no.4
• /
• pp.251-256
• /
• 2003

Indium aluminum arsenide(InAlAs) was grown by molecular beam epitaxy on (001) indium phosphide (InP) substrate and the effects of growth temperature on the properties of epitaxial layers were studied. In the temperature range of 370-$400 ^{\circ}C$, we observed that the surface morphology, optical quality and structural quality of InAlAs epilayers were improved as growth temperature increased. However, the InAlAs epilavers grown at $430 ^{\circ}C$ have the bad surface morphology and show the same trends as structural and epical quality. As a result of these measurements, it is suggested that the InAlAs epilayers of very good properties can be grown at $400 ^{\circ}C$.

• Food Science and Industry
• /
• v.51 no.4
• /
• pp.313-324
• /
• 2018

As excessive intake of salt is regarded as a reason for health problems, the tendency of people to attempt to reduce intake of salt in their everyday lives is on the rise. In Korea, where many people have a higher intake of salt compared to those in other countries, there have been diverse efforts to improve on this eating habit. Protein hydrolysates are chemically, physically hydrolyzed protein that have been widely utilized as a material for not only regular food but health functional food due to have diverse biological effects such as anti-oxidation, anti-inflammation, prevention of diabetes, and regulation of blood pressure. Various amino acids such as glutamic acid, arginine and arginine dipeptides, which exist in the components of protein hydrolysates, have also been recently recognized as being helpful in decreasing the use of salt in foods as they can greatly enhance salty taste when used concurrently with salt due to having both salty and palatable flavors. In the case of protein hydrolysates that decompose soy protein or fish protein such as anchovy, they could reduce consumption of salt by as much as 50% without affecting people's food preferences when applied to food as they boost salty taste by approximately 10% to 70%. Although there are only a few studies on protein hydrolysates as a salty taste enhancer or salt substitute, the results of several studies are indicative of the potential of protein hydrolysates as a salty taste enhancing ingredient.

• Journal of the Korean Vacuum Society
• /
• v.22 no.2
• /
• pp.86-91
• /
• 2013

The optical properties of InAs quantum dots (QDs) grown on GaAs substrates grown by molecular beam epitaxy have been studied using photoluminescence (PL) and time-resolved PL measurements. InAs QDs were grown using an arsenic interruption growth (AIG) technique, in which the As flux was periodically interrupted by a closed As shutter during InAs QDs growth. In this study, the shutter of As source was periodically opened and closed for 1 (S1), 2 (S2), or 3 s (S3). For comparison, an InAs QD sample (S0) without As interruption was grown in a pure GaAs matrix for 20 s. The PL intensity of InAs QD samples grown by AIG technique is stronger than that of the reference sample (S0). While the PL peaks of S1 and S2 are redshifted compared to that of S0, the PL peak of S3 is blueshifted from that of S0. The increase of the PL intensity for the InAs QDs grown by AIG technique can be explained by the reduced InAs clusters, the increased QD density, the improved QD uniformity, and the improved aspect ratio (height/length). The redshift (blueshift) of the PL peak for S1 (S3) compared with that for S0 is attributed to the increase (decrease) in the QD average length compared to the average length of S0. The PL intensity, PL peak position, and PL decay time have been investigated as functions of temperature and emission wavelength. S2 shows no InAs clusters, the increased InAs QD density, the improved QD uniformity, and the improved QD aspect ratio. S2 also shows the strongest PL intensity and the longest PL decay time. These results indicate that the size (shape), density, and uniformity of InAs QDs can be controlled by using AIG technique. Therefore the emission wavelength and luminescence properties of InAs/GaAs QDs can also be controlled.