• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.299-299
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• 2016

SiC는 넓은 에너지갭 (Eg=~3.4 eV)을 갖는 반도체로써, 고전압, 고온에서 동작이 가능하여 기존의 Si기반의 파워디바이스를 대체하기 위한 물질로 많은 연구가 이루어지고 있다. 파워 디바이스의 성능 향상을 위해서는 기판과 절연체 사이의 계면에 생성되는 계면 결함을 감소시켜야 한다. 따라서 본 연구에서는 SiC 기판에 high-k 물질인 HfO2를 증착하여 HfO2/SiC 계면에 유도된 결함을 분석하고 이를 감소시킬 수 있는 방법에 대한 연구를 수행하였다. HfO2 박막은 atomic-layer-deposition (ALD) 방법을 이용하여 SiC 기판 위에 $200^{\circ}C$에서 증착하였다. HfO2 박막 증착 후 NH3 분위기에서 rapid thermal annealing 방법을 이용하여 $600^{\circ}C$에서 1분 동안 열처리 진행하였다. Current-voltage (I-V) 측정을 통해 열처리 전 HfO2/SiC의 절연파괴 전압이 약 8.3 V 임을 확인하였다. NH3 열처리 후 HfO2/SiC의 절연파괴 전압이 10 V로 증가하였으며 누설 전류가 크게 감소하는 것을 확인하였다. 또한 capacitance-voltage (C-V) 측정을 통해 열처리 후 flat band voltage가 negative 방향에서 positive 방향으로 이동함을 확인하였고, 이를 통해 NH3 열처리 방법이 HfO2/SiC 계면에 존재하는 결함을 감소시킬 수 있음을 확인하였다. 전자 구조상의 conduction band edge에 존재하는 결함 준위를 분석하기 위해 x-ray absorption spectroscopy (XAS) 분석을 실시하였고, 열처리 전 HfO2/SiC 계면에 많은 결함 준위가 존재함을 확인하였으며, x-ray photoelectron spectroscopy (XPS) 분석을 통해 이 결함 준위가 oxygen deficiency state과 관련됨을 알 수 있었다. NH3 열처리 후 결과와 비교해보면, oxygen deficiency state가 감소함을 확인하였으며 이로 인해 conduction band edge에 존재하는 결함 준위가 감소함을 알 수 있었다. 따라서, NH3 열처리 방법을 이용하여 HfO2/SiC 계면에 존재하는 결함을 감소시킬 수 있으며, HfO2/SiC의 물리적, 전기적 특성을 향상시킬 수 있다는 결과를 도출하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.144-145
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• 2009

Single crystal $CdGa_2Se_4$ layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at $420^{\circ}C$ with the hot wall epitaxy (HWE) system by evaporating the poly crystal source of $CdGa_2Se_4$ at $630\;^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $CdGa_2Se_4$ thin films measured with Hall effect by van der Pauw method are $8.27\;\times\;10^{17}\;cm^{-3}$, $345\;cm^2/V{\cdot}s$ at 293 K, respectively. The photocurrent and the absorption spectra of $CdGa_2Se_4$/SI(Semi-Insulated) GaAs(100) are measured ranging from 293 K to 10K. The temperature dependence of the energy band gap of the $CdGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 2.6400 eV - ($7.721\;{\times}\;10^{-4}\;eV/K)T^2$/(T + 399 K). Using the photocurrent spectra and the Hopfield quasi cubic model, the crystal field energy(${\Delta}cr$) and the spin-orbit splitting energy(${\Delta}so$) for the valence band of the $CdGa_2Se_4$ have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the $A_1$-, $B_1$-, and $C_{11}$-exciton peaks.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.226-229
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• 2004

A stoichiometric mixture of evaporating materials for $CuAlSe_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CuAlSe_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $680^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuAlSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.24{\times}10^{16}\;cm^{-3}$ and $295\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuAlSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;=\;2.8382\;eV\;-\;(8.68{\times}10^{-4}\;eV/K)T^2/(T+155K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $CuAlSe_2$ have been estimated to be 0.2026 eV and 0.2165 eV at 10K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_5$ states of the valence band of the $CuAlSe_2$. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.403-409
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• 2013

In this work, a CMOS two stage differential power amplifier which includes Marchand balun, transformer and injection-locked buffer is presented. The power amplifier is targeted for 70 GHz frequency band and fabricated using 65 nm technology. The measurement results show 8.5 dB maximum voltage gain at 71.3 GHz and 7.3 GHz 3 dB bandwidth. The measured maximum output power is 8.2 dBm, input $P_{1dB}$ is -2.8 dBm, output $P_{1dB}$ is 4.6 dBm and maximum power added efficiency is 4.9 %. The power amplifier consumes 102 mW DC power from 1.2 V supply voltage.

• Korean Chemical Engineering Research
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• v.49 no.1
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• pp.95-100
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• 2011

During the development of low band-gap organic materials(p-type semiconducting organic compounds) for organic solar cells, an oligomer consisting of 2,5-dioctyloxyphenylene(OP), 3-hexylthiophene(HT), and 2,3-dimethylthieno[ 3,4-b]pyrazine(TP) as repeat units, oligo(OP-HT-TP), was synthesized. The oligomer was amorphous in nature in the temperature range studied, and well soluble in common organic solvents such as chloroform. The maximum absorption wavelength was 716 nm in solid state. The band-gap and HOMO/LUMO energy levels of oligo(OP-HT-TP) were measured to be 1.20 eV and -5.27/4.04 eV, respectively. However, the absorbance of the oligomer at maximum absorption wavelength was less than one fifth of that of poly(3-hexylthiophene) which has been most frequently used in fabrication of organic solar cells.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.74-75
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• 2005

ZnO epilayer were synthesized by the pulesd laser deposition(PLD) process on $Al_2O_3$ substrate after irradiating the surface of the ZnO sintered pellet by the ArF(193 nm) excimer laser. The epilayers of ZnO were achieved on sapphire ($Al_2O_3$) substrate at a temperature of $400^{\circ}C$. The crystalline structure of epilayer was investigated by the photoluminescence. The carrier density and mobility of ZnO epilayer measured with Hall effect by van der Pauw method are $8.27{\times}10^{16}cm^{-3}$ and $299cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the ZnO obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 3.3973 eV - ($2.69{\times}10^{-4}$ eV/K)$T_2$/(T + 463 K). The crystal field and the spin-orbit splitting energies for the valence band of the ZnO have been estimated to be 0.0041 eV and 0.0399 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the $\triangle$so definitely exists in the $\ulcorner_6$ states of the valence band of the ZnO. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.

• Transactions on Electrical and Electronic Materials
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• v.12 no.4
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• pp.164-168
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• 2011

Nanocrystalline cadmium sulphide (CdS) thin films were prepared using chemical bath deposition (CBD), and the structural, optical and photoconductive properties were investigated. The crystal structure of CdS thin film was studied by X-ray diffraction. The crystallite size, dislocation density and lattice constant of CBD CdS thin films were investigated. The dislocation density of CdS thin films initially decreases with increasing film thickness, and it is nearly constant over the thickness of 2,500 ${\AA}$. The dislocation density decreases with increasing the crystallite size. The Urbach energies of CdS thin films are obtained by fitting the optical absorption coefficient. The optical band gap of CdS thin films increases and finally saturates with increasing the lattice constant. The Urbach energy and optical band gap of the 2,900 A-thick CdS thin film prepared for 60 minutes are 0.24 eV and 2.83 eV, respectively. The activation energies of the 2,900 ${\AA}$-thick CdS thin film at low and high temperature regions were 14 meV and 31 meV, respectively. It is considered that these activation energies correspond to donor levels associated with shallow traps or surface states of CdS thin film. Also, the value of ${\gamma}$ was obtained from the light transfer characteristic of CdS thin film. The value of ${\gamma}$ for the 2,900 A-thick CdS thin film was 1 at 10 V, and it saturates with increasing the applied voltage.

• ETRI Journal
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• v.27 no.1
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• pp.75-80
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• 2005

This paper addresses a fully-integrated low phase noise X-band oscillator fabricated using a carbon-doped InGaP heterojunction bipolar transistor (HBT) GaAs process with a cutoff frequency of 53.2 GHz and maximum oscillation frequency of 70 GHz. The oscillator circuit consists of a negative resistance generating circuit with a base inductor, a resonating emitter circuit with a microstrip line, and a buffering resistive collector circuit with a tuning diode. The oscillator exhibits 4.33 dBm output power and achieves -127.8 dBc/Hz phase noise at 100 kHz away from a 10.39 GHz oscillating frequency, which benchmarks the lowest reported phase noise achieved for a monolithic X-band oscillator. The oscillator draws a 36 mA current from a 6.19 V supply with 47.1 MHz of frequency tuning range using a 4 V change. It occupies a $0.8mm{\times}0.8mm$ die area.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.3
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• pp.438-445
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• 2017

This paper presents a low-power high-resolution band-pass ${\Sigma}{\Delta}$ ADC for accelerometer applications. The proposed band-pass ${\Sigma}{\Delta}$ ADC consists of a high-performance 6-th order feed-forward ${\Sigma}{\Delta}$ modulator with 1-bit quantization and a low-power, area-efficient digital filter. The ADC is fabricated in 180 nm 1P6M mixed-signal CMOS process with a die area of $5mm^2$. This high-resolution ADC got 90 dB peak signal to noise plus distortion ratio (SNDR) and 96 dB dynamic range (DR) over 4 kHz bandwidth, while the intermediate frequency (IF) is shifting from 100 KHz to 200 KHz. The power dissipation of the chip is 5.6 mW under 1.8 V (digital)/3.3 V (analog) power supply.

• 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.