• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.2
• /
• pp.120-129
• /
• 1995

A new nethod, namely multi-gain-levering, is proposed to improve FM response of the single frequency semiconductor lasers and applied to 1.55$\mu\textrm{m}$ InGaAsP/InP MGL(multi-gain-levered)-MQW-DFB-LD. This device consists of three sections with different bandgap energy and can be easily realized by selective MOVPE growth. Our analysis based on Green function showed that a flat, red-shifted, high FM efficiency of aove 15GHz/mA can be extected by novel gain-levering scheme.

• Journal of the Optical Society of Korea
• /
• v.2 no.1
• /
• pp.13-21
• /
• 1998

Based on the escape cone concepts, high-brightness light-emitting diodes (LEDs) have been analyzed. In AlGaAs or InGaAlP LEDs, photon absorption in the ohmic region under the electrode is known to be significant. Thus, ins general, a thick window layer (WL) and a transparent substrate (TS) would minimize photon shielding by the electrodes and considerably improve photon output coupling efficiency. However, the schemes do not seem to be necessary in InGaN system. Photon absorption in ohmic contact to a wide bandgap semiconductor such as GaN may be negligible and, as a result, the significant photon shielding by the electrodes will not degrade the photon output coupling efficiency so much. The photon output coupling efficiency estimated in InGaN LEDs is about 2.5 - 2.8 times that of the conventional high-brightness LED structures based on both WL and TS schemes. As a result, the extenal quantum efficiency in InGaN LEDs is as high as 9% despite the presumably very low internal quantum efficiency.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.612-612
• /
• 2013

The band-gap opening in graphene is a key factor in developing graphene-based field effect transistors. Although graphene is a gapless semimetal, a band-gap opens when graphene is formed into a graphene nanoribbon (GNR). Moreover, the band-gap energy can be manipulated by the width of the GNR. In this study, we propose a site-specific synthesis of a width-tailored GNR directly onto an insulating substrate. Predeposition of a diamond-like carbon nanotemplate onto a SiO2/Si wafer via focused ion beam-assisted chemical vapor deposition is first utilized for growth of the GNR. These results may present a feasible route for growing a width-tailored GNR onto a specific region of an insulating substrate.

• Journal of Surface Science and Engineering
• /
• v.41 no.1
• /
• pp.28-32
• /
• 2008

In this paper CdS thin films, which were widely used window layer of the CdS/CdTe and the CdS/$CuInSe_2$ heterojunction solar cell, were grown by chemical bath deposition, which is a very attractive method for low-cost and large-area solar cells, and the structural, optical and electrical properties of the films was studied. As the thiourea/$CdAc_2$ mole ratio was increased, the deposition rate of CdS films prepared by CBD was increased due to increasing reaction velocity in solution and the optical bandgap was increased at higher thiourea/$CdAc_2$ mole ratio due to larger grain size and continuous microstructure. The minimum resistivity of the films was at thiourea/$CdAc_2$ mole ratio of 3.

• Journal of Surface Science and Engineering
• /
• v.44 no.2
• /
• pp.39-43
• /
• 2011

Amorphous silicon thin film was deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD). Each films were prepared in different dilution in the chamber gas. As a result, silicon crystallites and crystal volume fraction was increased with raising the hydrogen dilution in the gas and optical band gap was decreased. Increasement of the hydrogen contents in the chamber affected on surface roughness. In this study, thickness and surface roughness of the a-Si thin film by different hydrogen dilution was investigated by various techniques.

• Proceedings of the IEEK Conference
• /
• summer
• /
• pp.19-22
• /
• 2004

The goal of this study is to realize the PBG lowpass filter using novel PBG structure modification both upper layer and ground layer. It has been designed three aperture slots of ground layer for PBG structure which the center slot shape of ground is two type, rectangular and dumbbell. This PBG LPF has the character of the broader stopband and smaller size than typical LPF. The measurement results have matched the simulated ones. It has the cutoff frequency of each 4.465GHz and 3.52GHz and at least -20dB of the signal suppression at the stopband

• Proceedings of the IEEK Conference
• /
• 2006.06a
• /
• pp.69-70
• /
• 2006

Air-guided single-mode propagation of THz radiation in a photonic crystal waveguide (PCW) has been experimentally demonstrated for the first time. The PCW has been fabricated by introducing an air defect at the center of an air/Si 1D photonic crystal. By using a THz time-domain spectroscopic technique, we have experimentally shown that the guiding mechanism of the air-guiding PCW is the photonic bandgap effect.

• Proceedings of the IEEK Conference
• /
• 2006.06a
• /
• pp.485-486
• /
• 2006

This paper proposes a novel low-cost CMOS temperature sensor for controlling the self-refresh period of a mobile DRAM. In this temperature sensor, ring oscillators composed of cascaded inverter stages are used to obtain the temperature of the chip. This method is highly area-efficient, simple and easy for IC implementation as compared to traditional temperature sensors based on analog bandgap reference circuits. The proposed CMOS temperature sensor was fabricated with 80 nm 3-metal DRAM process. It occupies a silicon area of only about less than $0.02\;mm^2$ at $10^{\circ}C$ resolution with under 5uW power consumption at 1 sample/s processing rate. This area is about 33% of conventional temperature sensor in mobile DRAM.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2009.10a
• /
• pp.1428-1429
• /
• 2009

Compared to the indium zinc oxide (IZO) film fabricated by micro-powder target, the IZO film with nano-powder target exhibited improved optoelectronic properties of wide bandgap, high transmittance, surface uniformity, and low sheet resistance due to the high film density.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.5
• /
• pp.422-426
• /
• 2006

[ $Sr_xCa_{(1-x)}TiO_3$ ] red phosphors doped with Pr(0.13 mol%) and Al(0.23 mol%) were synthesized by solid state reaction method. Change of crystal structure occurred in $Sr_xCa_{(1-x)}TiO_3:Pr,Al$ phosphors with increasing value of x. Green and red luminescence were observed from $SrTiO_3:Pr,Al$ phosphors at low temperature. However, only red luminescence in the case of $CaTiO_3:Pr,Al$ phosphors was measured at low temperature. The main cause of green luminescence was explained by the bandgap reduction.