• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.11
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• pp.1672-1678
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• 1989

Major problems preventing the device-quality GaAs/Si heterostructure are the lattice mismatch of about 4% and difference in thermal expansion coefficient by a factor of 2.64 between Si and GaAs. Ge is a good candidate for the buffer layer because its lattice parameter and thermal expansion coefficient are almost the same as those of GaAs. As a first step toward developing heterostructure such as GaAs/Ge/Si entirely by a home-built PAE (plasma-assisted epitaxy), Ge films have been deposited on p-type Si (100)substrate by the plasma assisted evaporation of solid Ge source. The characteristics of these Ge/Si heterostructure were determined by X-ray diffraction, SEM and Auge electron spectroscope. PAE system has been successfully applied to quality-good Ge layer on Si substrate at relatively low temperature. Furthermore, this system can remove the native oxide(SiO2) on Si substrate with in-situ cleaning procedure. Ge layer grown on Si substrate by PAE at substrate temperature of 450\ulcorner in hydrogen partial pressure of 10mTorr was expected with a good buffer layer for GaAs/Ge/Si heterostructure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.7
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• pp.551-556
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• 2000

We have investigated the effect of surface In composition with Si cell temperature on the In$_{0.1}$/Ga$_{0.9}$/As epilayers grown on GaAs substrates. The epilayers were grown by molecular beam epitaxy(MBE) method and were characterized by the pthotoreflectance(PR) measurements. The E$_{o}$ bandgap energies of In$_{0.1}$/Ga$_{0.9}$/As epilayers were observed at around 1.28 eV at room temperature, and the additional shoulder peaks appeared at the higher energies than E$_{o}$ with increase of Si doping concentrations. The intensity of the additional shoulder peak was decreased with lowering the measurement temperature and the peak disappeared with the increase of surface etching time. This results hows that In composition at surface of InGaAs epilayer is decreased with the increase of the doping cell temperature. We consider that the reason of the decrease of In composition at the surface should be due to In re-evaporation from the surface by radiation heat of Si doping cell.ell.ell.ell.

• Current Photovoltaic Research
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• v.4 no.3
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• pp.108-113
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• 2016

III-V compound semiconductor based thin film solar cells promise relatively higher power conversion efficiencies and better device reliability. In general, the thin film III-V solar cells are fabricated by an epitaxial lift-off process, which requires an $Al_xGa_{1-x}As$ ($x{\geq}0.8$) sacrificial layer and an inverted solar cell structure. However, the device performance of the inversely grown solar cell could be degraded due to the different internal diffusion conditions. In this study, InGaP/GaAs double-junction solar cells are inversely grown by MOCVD on GaAs (100) substrates. The thickness of the GaAs base layer is reduced to minimize the thermal budget during the growth. A wide band gap p-AlGaAs/n-InGaP tunnel junction structure is employed to connect the two subcells with minimal electrical loss. The solar cell structures are transferred on to thin metal films formed by Au electroplating. An AlAs layer with a thickness of 20 nm is used as a sacrificial layer, which is removed by a HF:Acetone (1:1) solution during the epitaxial lift-off process. As a result, the flexible InGaP/GaAs solar cell was fabricated successfully with an efficiency of 27.79% under AM1.5G illumination. The efficiency was kept at almost the same value after bending tests of 1,000 cycles with a radius of curvature of 10 mm.

• ETRI Journal
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• v.13 no.4
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• pp.70-79
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• 1991

$In_1-x$$GA_X$$As_y$$P_1-y$ has a very wide range of applications in optoelectronic devices especially for optical communications because $In_1-x$$GA_X$$As_y$$P_1-y$ has the bandgap of the lowest dispersion ($1.3\mum$) and the lowest loss ( $1.55\mum$) of the optical fiber by changing the composition. The quality of $In_1-x$$GA_X$$As_y$$P_1-y$ epitaxial layer is believed to have a significant effect on the performance of device. The OMVPE growth conditions for the latticematched $In_1x$$GA_X$$As_y$$P_1-y$/InP were investigated. Effects of growth conditions such as V/III ratio, growth temperature, and Ga source material on the electrical and optical properties were studied. The composition, electrical and optical properities of $In_1-x$$GA_X$$As_y$$P_1-y$ were characterized using double crystal X-ray diffractometer (DCD), photoluminescence (PL), XPS(ESCA) and Hall measurement.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.60.1-60.1
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• 2007

• Journal of the Microelectronics and Packaging Society
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• v.6 no.1
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• pp.1-10
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• 1999

InGaP epilayers were grown on the flat, $2^{\circ}$off, $6^{\circ}$ off, and $10^{\circ}$off GaAs substrates by organo-metallic vapor phase epitaxy, and influences of crystallographic misorientation of the substrate on the structural and optical properties such as lattice mismatch, elastic strain, lattice curvature, misfit stress, and PL intensity /line-width were investigated in this study. Material characterizations were carried out by TXRD( tripple-axis x-ray diffractometer) and low temperature (11K) PL (photoluminescence). With increase of the substrate misorientation angle (S.M.A.), the relative incorporation of Ga atoms on the substrate surface was found to be enhanced. Also, with increase of the S. M. A., the x-ray line-width of the InGaP epilayer was reduced, indicating that the crystal quality of the epilayer could be improved tilth a misoriented substrate. It was also found that the elastic accommodation of the strain-free lattice misfit was more remarkable in a misoriented sample. PL intensity increased, and PL line-width and emission wavelength decreased with the increase of S. M. A. The results conclude that the elastic characteristics and the crystal quality of the InGaP epilayer could be remarkably enhanced when the misoriented substrates were employed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.636-639
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• 2001

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InGaN well and GaN barrier by metal-organic chemical vapor deposition were investigated using photoluminescence, high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The luminescence intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blue shift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher intensity and lower energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.

• Journal of Microbiology and Biotechnology
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• v.20 no.1
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• pp.202-207
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• 2010

Plant growth promoting fungi (PGPF) are well known for the production of useful secondary metabolites. However, limited information is available on the gibberellin (GA) production capacity of PGPF of endophytic origin. In the current study, 15 fungal endophytes were isolated from the roots of Crown daisy, and then screened on Waito-c rice, in order to identify plant growth promoting fungi. The fungal isolate MH7 significantly increased the shoot length (12.1 cm) of Waito-c in comparison with control treatment (7.9 cm). In a separate experiment, the culture filtrate (CF) of MH7 significantly promoted the growth attributes of Crown daisy. The MH7 CF was analyzed for gibberellins and it contained all physiologically active gibberellins ($GA_1$, 1.37 ng/ml; $GA_3$, 5.88 ng/ml; $GA_4$, 8.62 ng/ml; and $GA_7$, 2.05 ng/ml) in conjunction with physiologically inactive $GA_9$ (0.83 ng/ml), $GA_{12}$ (0.44 ng/ml), $GA_{15}$ (0.74 ng/ml), $GA_{19}$ (1.16 ng/ml), and $GA_{20}$ (0.98 ng/ml). The CF of MH7 produced higher amounts of $GA_3$, $GA_4$, $GA_7$, $GA_9$, and $GA_{12}$ than wild-type Fusarium fujikuroi, which was used as a control for GA production. The fungal isolate MH7 was later identified as a new strain of Penicillium on the basis of its morphological characteristics and phylogenetic analysis of the 188 rDNA sequence.

• Journal of Electrical Engineering and information Science
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• v.3 no.2
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• pp.239-244
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• 1998

Piezoelectric pressure sensors and pyroelectric infrared detectors based on ZnO thin film have been integrated with GaAs metal-semiconductor field effect transistor (MESFET) amplifiers. Surface micromachining techniques have been applied in a GaAs MESFET process to form both microsensors and electronic circuits. The on-chip integration of microsensors such as pressure sensors and infrared detectors with GaAs integrated circuits is attractive because of the higher operating temperature up to 200 oC for GaAs devices compared to 125 oC for silicon devices and radiation hardness for infrared imaging applications. The microsensors incorporate a 1${\mu}$m-thick sputtered ZnO capacitor supported by a 2${\mu}$m-thick aluminum membrane formed on a semi-insulating GaAs substrate. The piezoelectric pressure sensor of an area 80${\times}$80 ${\mu}$m2 designed for use as a miniature microphone exhibits 2.99${\mu}$V/${\mu}$ bar sensitivity at 400Hz. The voltage responsivity and the detectivity of a single infrared detector of an area 80${\times}$80 $\mu\textrm{m}$2 is 700 V/W and 6${\times}$108cm$.$ Hz/W at 10Hz respectively, and the time constant of the sensor with the amplifying circuit is 53 ms. Circuits using 4${\mu}$m-gate GaAs MESFETs are fabricated in planar, direct ion-implanted process. The measured transconductance of a 4${\mu}$m-gate GaAs MESFET is 25.6 mS/mm and 12.4 mS/mm at 27 oC and 200oC, respectively. A differential amplifier whose voltage gain in 33.7 dB using 4${\mu}$m gate GaAs MESFETs is fabricated for high selectivity to the physical variable being sensed.

• Journal of the Korean Vacuum Society
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• v.11 no.1
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• pp.43-49
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• 2002

Pd/Ge/Pd/Ti/Au ohmic contact to n-type InGaAs was investigated with rapid thermal annealing conditions. Minimum specific contact resistivity of $1.1\times10^{-6}\Omega\textrm{cm}^2$ was achieved after annealing at $400^{\circ}C$/10sec, and a ohmic performance was degraded at higher annealing temperature due to the chemical reaction between the ohmic contact materials and the InGaAs substrate. However, non-spiking planar interface and relatively good ohmic contact($high-10^{-6};{\Omega}\textrm{cm}^2$) were maintained. This ohmic contact system is expected to be a promising candidate for compound semiconductor devices.