• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.588-593
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• 2014

Current crowding problem can worsen the internal quantum efficiency and the negative-voltage ESD of InGaN-based LEDs. In this paper, by using photon emission microscope and thermal emission microscope measurement, we confirmed that the electric field and the current of the InGaN-based LED sample are crowded in specific regions where the distance between p-type metal contact and n-type metal contact is shorter than other regions. To improve this crowding problem of electric field and current, modified metal contact geometry having uniform distance between the two contacts is proposed and verified by a numerical simulation. It is confirmed that the proposed structure shows better current spreading, resulting in higher internal quantum efficiency and reduced reverse leakage current.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.321-329
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• 2012

Providing variable load for testing a motor in high speed conditions is usually a difficult task. The eddy current brake can be used in application of load testing of motors. This paper deals with construction of a novel claw pole eddy current brake which is employed as a load for a DC counter rotating motor (CRM). These kinds of motors have two inner and outer shafts that rotate in opposite directions simultaneously, which are particularly suitable for under water propulsion systems. The prototype 45KW eddy current brake consists of two parts. One of them is installed on the inner shaft of the 60KW DC CRM and the other one is installed on its outer shaft. The simulation and experimental results with prototype brakes are also analyzed by using MATLAB/Simulink and the operational characteristic of the brake is demonstrated as a function of the motor speed and current of the magnetic poles.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.347-348
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• 2013

To obtain high conversion efficiency in InGaN-based solar cells, it is critical to grow high indium (In) composed InGaN layer for increasing sun light absorption wavelength rage. At present, most InGaN-based solar cells adopt InGaN/GaN multi-quantum-well (MQW) structure for high crystalline quality of InGaN with high In composition. In this study, we fabricated and compared the performances of two types of InGaN/GaN MQW solar cells which have the 15% (SC 15) and 25% (SC 25) of In composition at quantum well layer. Although both devices showed similar dark current density and leakage current, SC 15 showed better performance under AM 1.5G illumination as shown in Fig. 1. It is interesting to note that SC 25 showed severe current density decrease as increasing voltages. As a result, it lowered short circuit current density and fill factor of the device. However, SC 15 showed steady current density and over 75 % of fill factor. To investigate these differencesmore clearly, we analyzed their photoluminescence (PL) spectra under various applied voltages as shown in Fig. 2. At the same time, photocurrent, which was generated by PL excitation, was also measured as shown in Fig. 3. Further, we investigated the relationship between piezoelectric field and performance of InGaN based solar cell varying indium composition.

• Progress in Superconductivity
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• v.9 no.2
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• pp.152-156
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• 2008

Detailed field and strain dependence of the critical current and the n-value for an internal-tin processed $Nb_3Sn$ strand have been measured. Both the compressive and tensile strain is applied reversibly using Walter spiral probe made of BeCu up to 0.73 %. There is a correlation between the critical current and the n-value for the $Nb_3Sn$ strand studied in this work and the field dependence of the n-value is in agreement with a recent empirical formula. It was further shown that the critical current can be reasonably well fitted by the scaling law based on strong-coupling theory of superconductivity using the relation between the critical current and the n-value.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.2
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• pp.14-19
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• 2011

We have fabricated GaN Schottky barrier diode (SBD) for high-voltage applications on Si substrate. The leakage current and the electrical characteristics of GaN SBD are investigated by annealing metal-semiconductor junctions. Ohmic junctions of Ti/Al/Mo/Au and Schottky junctions of Ni/Au are used in the fabrication. A test structure is proposed to measured buffer leakage current through a mesa structure. When annealing temperature is increased from $700^{\circ}C$ to $800^{\circ}C$, measured buffer leakage current is also increased from 87 nA to 780 nA at the width of 100 ${\mu}m$. The diffusion of Au, Ti, Mo, O into GaN buffer layer increases the leakage current and that is verified by Auger electron spectroscopy. Experimental results show that the low leakage current and the high breakdown voltage of GaN SBD are achieved by annealing metal-semiconductor junctions.

• The Journal of the Korea institute of electronic communication sciences
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• v.3 no.2
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• pp.79-85
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• 2008

It is important to consider the life of battery and low power operation for various wireless communications. Thus, Analog current-mode signal processing with SI circuit has been taken notice of in designing the LSI for wireless communications. However, in current mode signal processsing, current memory circuit has a problem called clock-feedthrough. In this paper, we examine the connection of CMOS switch that is the common solution of clock-feedthrough and calculate the relation of width between CMOS switch for design methodology for improvement of current memory. As a result of simulation, when the width of memory MOS is 20um, ratio of input current and bias current is 0.3, the width relation in CMOS switch is obtained with $W_{Mp}=5.62W_{Mn}+1.6$, for the nMOS width of 2~6um in CMOS switch. And from the same simulation condition, it is obtained with $W_{Mp}=2.05W_{Mn}+23$ for the nMOS width of 6~10um in CMOS switch. Then the defined width relation of MOS transistor will be useful guidance in design for improvement of current memory.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.752-758
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• 2004

This paper reports on the DC and RF characteristics of AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beau epitaxy(MBE) on sapphire substrates. The devices with a 0.5 ${\mu}$m gate-length exhibited relatively flat transconductance(g$\_$m/), which results from the enhanced carrier confinement of the InGaN channel. The maximum drain current was 880 mA/mm with a peak g$\_$m/ of 156 mS/mm, an f$\_$T/ of 17.3 GHz, and an f$\_$MAX/ or 28.7 GHz. In addition to promising DC and RF results, pulsed I-V and current-switching measurements showed little dispersion in the unpassivated AlGaN/InGaN HEMTs. These results suggest that the addition of In to the GaN channel improves the electron transport characteristics as well as suppressing current collapse that is related to the surface trap states.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.11
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• pp.29-34
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• 2004

This paper reports the RF dispersion and linearity characteristics of unpassivated AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE). The devices with a 0.5 ${\mu}{\textrm}{m}$ gate-length exhibited relatively good DC characteristics with a maximum drain current of 730 mA/mm and a peak g$_{m}$ of 156 mS/mm. Highly linear characteristic was observed by relatively flat DC transconductance (g$_{m}$) and good inter-modulation distortion characteristics, which indicates tight channel carrier confinement of the InGaN channel. Little current collapse in pulse I-V and load-pull measurements was observed at elevated temperatures and a relatively high power density of 1.8 W/mm was obtained at 2 GHz. These results indicate that current collapse related with surface states will not be a power limiting factor for the AlGaN/InGaN HEMTs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.481-485
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• 2002

In this study, we fabricated the PBH-LD by meltback method using the LPE. The PBH-LDs are analyzed the leakage current that flows through leakage current path like the p-n diode and p-n-p-n current blocking layer. We observed the variation of threshold current with the leakage width $W_{ι}$. As a consequence, we confirmed that the threshold current became low in the decrease of the leakage width and in the increase of the ratio of specific resistivity of leakage region to active region. We also compared between the calculated threshold current in the absence of leakage region and the measured threshold current in the device. As a result, the ratio of specific resistivity was about 0.5 in the measured LDs, which have the width of a active layer of 1.4${\mu}{\textrm}{m}$ and leakage width of 0.6${\mu}{\textrm}{m}$.

• Current Optics and Photonics
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• v.4 no.4
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• pp.380-390
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• 2020

In this study, the traditional electron-blocking layer (EBL) in (In,Ga)N/GaN light-emitting diodes is replaced by a circular EBL that is the same size as the n-pad. The three-dimensional (3D) nonlinear Poisson, drift-diffusion, and continuity equations are adopted to simulate current transport in the LED and its characteristics. The results indicate that the local carrier-density distribution obtained for the circular EBL design is more uniform than that for the traditional EBL design. This improves the uniformity of local radiative recombination and local internal quantum efficiency (IQE) at high injection levels, which leads to a higher lumped IQE and lower efficiency droop. With the circular EBL, the lumped IQE is higher in the outer active region and lower in the active region under the n-pad. Since most emissions from the active region under the n-pad are absorbed by the n-pad, obviously, an LED with a circular EBL will have a higher external quantum efficiency (EQE). The results also show that this LED works at lower applied voltages.