• Current Optics and Photonics
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• v.2 no.5
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• pp.468-473
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• 2018

We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to $80^{\circ}C$. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to $80^{\circ}C$, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.5
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• pp.71-78
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• 2011

In this paper, we describe the design and implementation of a high efficiency and broad-band Class-J mode power amplifier using gallium nitride(GaN) high-electron mobility transistor(HEMT). The matching circuit of proposed class-J mode power amplifier for 2nd harmonic impedance designed to provide pure reactance alone. The measurement results show that output power of $40{\pm}1$ dBm, power-added efficiency of 50%, and drain efficiency of 60% for a continuous wave signal at 1.4 to 2.6 GHz.

• Journal of Crop Science and Biotechnology
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• v.10 no.2
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• pp.57-63
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• 2007

Due to the strong influence of nitrogen(N) on plant productivity, a vast amount of N fertilizers is used to maximize crop yield. Over-use of N fertilizers leads to severe pollution of the environment, especially the aquatic ecosystem, as well as reducing farmer's income. Growing of N-efficient cultivars is an important prerequisite for integrated nutrient management strategies in both low- and high-input agriculture. Taking maize as a sample crop, this paper reviews the response of plants to low N stress, the physiological processes which may control N-use efficiency in low-N input conditions, and the genetic and molecular biological aspects of N-use efficiency. Since the harvest index(HI) of modern cultivars is quite high, further improvement of these cultivars to adapt to low N soils should aim to increase their capacity to accumulate N at low N levels. To achieve this goal, establishment and maintenance of a large root system during the growth period may be essential. To reduce the cost of N and carbon for root growth, a strong response of lateral root growth to nitrate-rich patches may be desired. Furthermore, a large proportion of N accumulated in roots at early growth stages should be remobilized for grain growth in the late filling stage to increase N-utilization efficiency. Some QTLs and genes related to maize yield as well as root traits have been identified. However, their significance in improving maize NUE at low N inputs in the field need to be elucidated.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.1
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• pp.62-70
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• 1984

N+NPP+ HLEBSF (high low emitter back surface field) solar cells which have N+N high low junction in the emitter as well as N+PP+ BSF cells were designed and fabricated by using <111> oriented P type Si wafers with the resistivity of 10$\Omega$/$\textrm{cm}^2$ and the thickness of 13-15 mil. Physical parameters (impurity concentration, thickness) at each region of N+PP+ and N+NPP+ cell were made equally through same masks and simultaneous process except N region of HLEBSF cell to investigate the high low emitter junction effect for efficiency improvement. Under the light intensity of 100 mW/$\textrm{cm}^2$, total area (active area) conversion efficiency were typically 10.94% (12.16%) for N+PP+ BSF cells and 12.07% (13.41%) for N+N PP+ cells. Efficiency improvement of N+NPP+ cell which has high low emitter Junction structure is resulted from the suppression of emitter recombination current and the increasement of open circuit voltage (Voc) and short circuit current (Ish) by removing heavy doping effects occurring in N+ emitter region.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.4
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• pp.327-332
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• 2009

In the devices structure of ITO/N,N'-diphenyl-N,N' bis (3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) /tris (8-hydroxyquinoline)aluminum$(Alq_3)$electron-transport-layer(ETL)(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP))/Al, we have studied the efficiency improvement of organic light-emitting diodes depending on the thickness variation of BCP using electron transport layer. The thickness of TPD and $Alq_3$ was manufactured 40 nm, 60 nm under a base pressure of $5{\times}10^{-6}$ Torr using at thermal evaporation, respectively. The TPD and $Alq_3$ layer were evaporated to be deposition rate of $2.5{\AA}/s$. And the BCP was evaporated to be a4 a deposition of $1.0{\AA}/s$. As the experimental results, we found that the luminous efficiency and the external quantum efficiency of the device is superior to others when thickness of BCP is 5 nm. Also, operating voltage is lowest. Compared to the ones from the devices without BCP layer, the luminous efficiency and the external quantum efficiency were improved by a factor of four hundred ninty and five hundred, respectively. And operating voltage is reduced to about 2 V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.349-350
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• 2008

In the structure of ITO/N,N'-diphenyl-N,N' bis (3-methylphenyl)-1,1'-biphenyl-4,4'-diamine(TPD) /2,9-Dimethy 1-4,7-diphenyl-1,10-phenanthroline (BCP)/tris (8-hydroxyquinoline)aluminum$(Alq_3)$/Al device, we studied the efficiency improvement of organic light-emitting diodes due to thickness variation of BCP materials used for a electron breaking layer. The thickness of TPD and $Alq_3$ was manufactured 40 nm, 60 nm, respectively under a base pressure of $5\times10^{-6}$Torr using a thermal evaporation. The TPD and $Alq_3$ layer were evaporated to be at a deposition rate of 2.0 A/s. The BCP was evaporated to be at a deposition of 1.0 A/s. When the thickness of BCP increased from 5 to 30 nm, we found that the luminous efficiency and the external quantum efficiency is superior to the others when the thickness of BCP is 20 nm. Compared to the ones from the devices made without BCP, the luminous efficiency and the external quantum efficiency was improved by 57 %, 70%, respectively.

• Asian Journal of Turfgrass Science
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• v.6 no.1
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• pp.23-28
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• 1992

Urea, the major N source of world agriculture involves a serious urea-N loss through NH$_3$volatilization. Approaches to decrease N loss include using urease inhibitors in view of the environmental protection and the increase of urea-N efficiency. The purpose of laboratory researches was toassess the potential value of urease inhibitors to increase urea-N efficiency in soil and Kentucky blue-grass(Poa Pratensis L.) turf. The activity of urease inhibitors Phenyiphosphorodiamjdate(ppD) and N-(n-butyl) thiophosphoric triamjde(NBPT) measured to break-down ammonia volatilization. The soil and turf used in this project were from the fairway in one of the Korean gof course. The researches were carried out for two weeks to measure the urease activities on urea hydrolysis under four temperatures (10~ 40$^{\circ}C$) and for one week on turfgrass using forced-draft system. Results indicated that Urea-N involves considerable loss through gaseous NH$_3$ by urease activities in plant-soil systems. Urease inhibitors PPD and NBPT have potential value for increasing N use efficiency by reduing NH$_3$ volatilization. NBPT deserves futher evaluation as fertilizer amendment than PPD use of urea in turf industries.

• ETRI Journal
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• v.38 no.1
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• pp.133-140
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• 2016

This paper presents a method of parasitic inductance reduction for high-speed switching and high-efficiency operation of a cascode structure with a low-voltage enhancement-mode silicon (Si) metal-oxide-semiconductor field-effect transistor (MOSFET) and a high-voltage depletion-mode gallium nitride (GaN) fielde-ffect transistor (FET). The method is proposed to add a bonding wire interconnected between the source electrode of the Si MOSFET and the gate electrode of the GaN FET in a conventional cascode structure package to reduce the most critical inductance, which provides the major switching loss for a high switching speed and high efficiency. From the measured results of the proposed and conventional GaN cascode FETs, the rising and falling times of the proposed GaN cascode FET were up to 3.4% and 8.0% faster than those of the conventional GaN cascode FET, respectively, under measurement conditions of 30 V and 5 A. During the rising and falling times, the energy losses of the proposed GaN cascode FET were up to 0.3% and 6.7% lower than those of the conventional GaN cascode FET, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.450-451
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• 2008

Amorphous silicon Solar cell has n-i-p structure in general, and each layer's thickness and doping concentration are very important factors which are as influential on efficiency of salar cell. Using AFORS HET simulation to get the high efficiency, by adjusting n layer's thickness and doping concentration, p layer's doping concentration. The optimized values are a-Si:H(n)'s thickness of 1nm, a-Si:H(n)r's doping concentration of $2\times10^{20}cm^{-3}$, a-Si:H(p+)r's doping concentration of $1\times10^{19}cm^{-3}$. After optimization, the solar cell shows $V_{oc}$=679.5mV, $J_{sc}$=39.02mA/$cm^2$, FF=83.71%, and a high Efficiency=22.21%. Though this study, we can use this study for planning or manufacturing solar cell which has high efficiency.

• Journal of environmental and Sanitary engineering
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• v.24 no.3
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• pp.7-15
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• 2009

The objective of this study was to investigate difference in nitrogen, organic, phosphorus and $NH_3$-N removal efficiency according to organic loading, comparing M-DEPHANOX process which has two nitrification reactor with M-eBNR process which has one nitrification reactor. As a result of this study, $NH_3$-N removal efficiency of M-DEPHANOX and M-eBNR resulted in average level of 91.8%, 96.9%, respectively. M-DEPHANOX and M-eBNR processes showed high removal efficiency in view of $NH_3$-N removal efficiency. Comparing organic removal efficiency by M-DEPHANOX and M-eBNR processes, the average removal efficiency in terms of TCOD, SCOD was 84.1%, 78.2% and 83.4%, 75.6%. Also, the results that observed about $NH_3$-N removal efficiency regarding organic loading revealed that nitrification reactor of RBC type are little influenced by flowing organic without precipitating at settling tank. Therefore, although inflow characteristics of municipal wastewater changes, M-eBNR process appeared to remove $NH_3$-N reliably.