• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.320-320
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• 2014

Amorphous silicon alloy (a-Si) solar cells and modules have been receiving a great deal of attention as a low-cost alternate energy source for large-scale terrestrial applications. Key to the achievement of high-efficiency solar cells using the multi-junction approach is the development of high quality, low band-gap materials which can capture the low-energy photons of the solar spectrum. Several cell designs have been reported in the past where grading or buffer layers have been incorporated at the junction interface to reduce carrier recombination near the junction. We have investigated profiling the composition of the a-SiGe alloy throughout the bulk of the intrinsic material so as to have a built-in electrical field in a substantial portion of the intrinsic material. As a result, the band gap mismatch between a-Si:H and $a-Si_{1-x}Ge_x:H$ creates a barrier for carrier transport. Previous reports have proposed a graded band gap structure in the absorber layer not only effectively increases the short wavelength absorption near the p/i interface, but also enhances the hole transport near the i-n interface. Here, we modulated the GeH4 flow rate to control the band gap to be graded from 1.75 eV (a-Si:H) to 1.55 eV ($a-Si_{1-x}Ge_x:H$). The band structure in the absorber layer thus became like a U-shape in which the lowest band gap was located in the middle of the i-layer. Incorporation of this structure in the middle and top cell of the triple-cell configuration is expected to increase the conversion efficiency further.

• Journal of environmental and Sanitary engineering
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• v.15 no.2
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• pp.102-111
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• 2000

As IR-sensor for detecting pollution material, the iron silicide has a fit band gap, high physicochemical stability at high temperature and good acid resistance. The growing film was formed with the Fe-Si bond and the organic compound because plasma resolved the injected precursors into various active species. In the Raman scattering spectrum, the Fe-Si vibration mode showed at 250 {TEX}$cm^{-1}${/TEX}. The FT-IR peak indicated that the various organic compounds were deposited on the films. The iron silicide was epitaxially grown to β-phase by the high energy of plasma. The lattice structure of films had [220]/[202] and [115]. The thickness of the films increased with the flow rate of silane. But rf-power increased with decreasing the thickness. The optical gap energy and the band gap were shown about 3.8 eV and 1.182∼1.194 eV. The band gap linearly increased and the formula was below: {TEX}$E_g^{dir}${/TEX}= 8.611×{TEX}$10^{-3}N_{D}${/TEX}＋1.1775

• 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.

• Transactions on Electrical and Electronic Materials
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• v.16 no.1
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• pp.5-9
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• 2015

Optical and electrical properties were studied for Antimony doped tin oxide thin films from precursors containing 10, 30, 50, and 70 atom% of Sb deposited on bare sodalime silica, barrier layer coated sodalime silica, and pure silica glass substrates by sol-gel spinning technique. The direct band gaps were found to vary from 3.13~4.12 eV when measured in the hv range of 2.5~5.0 eV, and varied from 4.22~5.08 eV when measured in the range of 4.0~7.0 eV. Indirect band gap values were in the range of 2.35~3.11 eV. Blue shift of band gap with respect to bulk band gap and Moss-Burstein shift were observed. Physical thickness of the films decreased with the increase in % Sb. Resistivity of the films deposited on SLS substrate was in the order of $10^{-2}$ ohm cm. Sheet resistance of the films deposited on barrier layer coated soda lime silica glass substrate was found to be relatively less.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.341-341
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• 2010

Electronic structure of Calix adsorbed on epitaxial graphene (EG) was investigated using high resolution photoemission spectroscopy (HRPES). Increasing the deposition of calix molecule, we found that EG becomes n-type doping using secondary edge measurement (work function change). As we observe bonding nature of O 1s peak, we found that single O 1s peak can be clearly distinguished in the spectra indicating equivalent adsorption state. Finally, we were able to control the band gap of EG using valence band spectra as we change the amount of calix molecule. In this study, we will propose the possibility of band gap modulation of EG using calix molecule.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2511-2513
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• 2007

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.376-376
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• 2010

The single crystals of p-$CdIn_2Te_4$ were grown by the Bridgman method without the seed crystal. From photocurrent measurements, it was found that three peaks, A, B, and C, correspond to the intrinsic transition from the valence band states of $\Gamma_7$(A), $\Gamma_6$(B), and $\Gamma_7$(C) to the conduction band state of $\Gamma_6$, respectively. The crystal field splitting and the spin orbit splitting were found to be 0.2360 and 0.1119 eV, respectively, from the photocurrent spectroscopy. The temperature dependence of the $CdIn_2Te_4$ band gap energy was given by the equation of $E_g(T)=E_g(0)-(9.43{\times}10^{-3})T^2/(2676+T)$. $E_g$(0) was estimated to be 1.4750, 1.7110, and 1.8229 eV at the valence band states of A, B, and C, respectively. The band gap energy of p-$CdIn_2Te_4$ at room temperature was determined to be 1.2023 eV.

• 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.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2333-2337
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• 2007

Nanoporous TiO2 and ZrO2 thin films were spin-coated using a surfactant-templated approach from Pluronic P123 (EO20PO70EO20) as the templating agent, titanium alkoxide (Ti(OC4H9)4) as the inorganic precursor, and butanol as a the solvent. The control of the electronic structure of TiO2 is crucial for its various applications. We found that the band gap of the hybrid nanoporous thin films can be easily tuned by adding an acetylacetonestabilized Zr(OC4H9)4 precursor to the precursor solution of Ti(OC4H9)4. Pores with a diameter of 5 nm-10 nm were randomly dispersed and partially connected to each other inside the films. TiO2 and ZrO2 thin films have an anatase structure and tetragonal structure, respectively, while the TiO2-ZrO2 hybrid film exhibited no crystallinity. The refractive index was significantly changed by varying the atomic ratio of titanium to zirconium. The band gap for the nanoporous TiO2 was estimated to 3.43 eV and that for the TiO2-ZrO2 hybrid film was 3.61 eV.