• Transactions on Electrical and Electronic Materials
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• v.6 no.5
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• pp.229-232
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• 2005

Direct characterization of band alignment at chemical bath deposition $(CBD)-CdS/Cu_{0.93}(In_{1-x}Ga_x)Se_2$ has been carried out by photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES). Ar ion beam etching at the condition of the low ion kinetic energy of 400 eV yields a removal of surface contamination as well as successful development of intrinsic feature of each layer and the interfaces. Especially interior regions of the wide gap CIGS layers with a band gap of $1.4\~1.6\;eV$ were successfully exposed. IPES spectra revealed that conduction band offset (CBO) at the interface region over the wide gap CIGS of x = 0.60 and 0.75 was negative, where the conduction band minimum of CdS was lower than that of CIGS. It was also observed that an energy spacing between conduction band minimum (CBM) of CdS layer and valance band maximum (VBM) of $Cu_{0.93}(In_{0.25}Ga_{0.75})Se_2$ layer at interface region was no wider than that of the interface over the $Cu_{0.93}(In_{0.60}Ga_{0.40})Se_2$ layer.

• Journal of Power Electronics
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• v.18 no.4
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• pp.985-996
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• 2018

The implementation and performance evaluation of an interleaved boundary conduction mode (BCM) boost power factor correction (PFC) converter is presented in this paper by employing three wide band-gap switching devices: a super junction silicon (Si) MOSFET, a silicon carbide (SiC) MOSFET and a gallium nitride (GaN) high electron mobility transistor (HEMT). The practical considerations for adopting wide band-gap switching devices to BCM boost PFC converters are also addressed. These considerations include the gate drive circuit design and the PCB layout technique for the reliable and efficient operation of a GaN HEMT. In this paper it will be shown that the GaN HEMT exhibits the superior switching characteristics and pronounces its merits at high-frequency operations. The efficiency improvement with the GaN HEMT and its application potentials for high power density/low profile BCM boost PFC converters are demonstrated.

• Journal of the Korean Vacuum Society
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• v.3 no.4
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• pp.420-425
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• 1994

메탄을 원료가스로 하여 PECVD에 의해 다이아몬드성 탄소(DLC) 박막을 형성하였으며 이때 인 가전력의 크기 및 주파수 그리고 보조가스의 종류가 optical band gap의 크기에 미치는 영향에 대학여 연구하였다. DLC 박막의 optical band gap 은 증착되는 이온의 에너지가 증가할수록 감하였으며 불활성 기체를 보조가스로 사용하는 경우 인가전력에 따른 optical band gap의 크기가 큰폭으로 감소하였다. 소 소를 보조가스로 사용한 경우는 높은 인가전력(100W 이상)에서 optical band gap이 증가하는 것으로 밝 혀졌으며 본 연구에서 제안된 증착 기수의 모델에 의해 적절한 설명이 가능하였다.

• Journal of information and communication convergence engineering
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• v.16 no.3
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• pp.197-202
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• 2018

This paper reveals the impact of the insertion of electromagnetic band gap (EBG) structures on the performance of circularly polarized (CP) patch-slot antenna with offset slot. Several optimizations are necessary to precise physical parameters in the aim to fix the resonance frequency at 3.2 GHz. The proposed antenna possesses lightweight, simplicity, low cost, and circular polarization ensured by two feeding sources to permit right-hand and left-hand circular polarization process (RHCP and LHCP). The measured results compared with simulation results of the proposed circularly polarized EBG antenna with offset slot show good band operations with –10 dB impedance bandwidths of 9.1% and 36.2% centered at 3.2 GHz, which cover weather radar, surface ship radar, and some communications satellites bands. Our investigation will confirm the simulation and experimental results of the EBG antenna involving new EBG structures.

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.05a
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• pp.78-78
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• 1996

• Carbon letters
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• v.28
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• pp.72-80
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• 2018

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on $CaCO_3$ was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature ($700^{\circ}C$), time (55 min), argon flow rate ($230.37mL\;min^{-1}$) and acetylene flow rate ($150mL\;min^{-1}$) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.337-340
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• 2001

We show that the microstrip ring with a narrow gap exhibits a photonic band gap (PBG) that is generally believed to be created by a periodic array. The discontinuity of impedance at the narrow gap induces the multiple reflections with fixed phase correlation necessary to make the PBG. We have also discussed the tuning of the PBG frequency by applying an external voltage on a varactor mounted on the gap and the applications of this PBG ring as a tunable bandstop filter and a microwave switch.

• Journal of electromagnetic engineering and science
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• v.6 no.2
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• pp.98-102
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• 2006

In this paper, we have designed and fabricated the high power amplifier employing PBG(Photonic Band-Gap Structure) to improve the linearity of the amplifier in the millimeter wave band. The fabricated amplifier using MMIC(TGA1073G) has operated about 24 GHz band and the PBG has resulted in 35 dB suppression about 49 GHz where the second harmonic occurs due to the amplifier. As a result, the output power has been 24.43 dBm and 13.2 dBc of the IMD has been improved. Also, the PAE is obtained to 14.96 % of the amplifier employing the PBG structure in Ka band.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.2
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• pp.167-175
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• 2013

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.388-391
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• 2015

본 연구에서는 탄소로 이루어진 그래핀과 붕소와 질소의 합성물인 h-BN을 적절하게 섞어, 밴드갭(band gap)의 변화를 범밀도함수이론(DFT)을 통하여 설계하려고 한다. 본 연구에서 태양전지의 가장 높은 효율을 가지기 위한 밴드갭 1.2eV 가지는 모델을 설계하려고 한다. Armchair 방향으로 B와 N을 도핑을 하여 width에 따른 Nanorribbons 형태를 만들어 밴드갭(band gap)의 변화를 살펴 볼 것이다. 그래핀과 h-BN을 각각 고정시키며 다른 한쪽의 width를 늘리면서 밴드갭(band gap)의 변화도 살펴 볼 것이다. 그래핀와 h-BN의 비가 5:3일 때 1.14eV로 가장 1.2eV에 비슷하게 나왔고 3:5일 때 1.12eV로 그 다음으로 가장 가까운 결과를 얻을 수 있엇다. 또한 비슷한 밴드갭을 가지더라도 그러한 원자 구조가 얼마나 안정적인지를 알기 위해 cohesive 에너지를 계산 할 것이다. 이러한 결과로 인해 태양에너지 연구에 큰 이바지를 할 수 있다.