• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1283-1285
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• 1997

In this paper, structural, optical and electrical properties of $Cd_{1-x}Zn_xS$ thin films prepared by co-evaporation method were studied. The crystal structure of $Cd_{1-x}Zn_xS$ films deposited at a substrate temperature of $150^{\circ}C$ was hexagonal with the c axis aligned perpendicular to the substrate. As increasing composition parameter x, the intensity of (002) peak decreased, which means poor crystalline and decreasing of preferential orientation. The optical bandgap of $Cd_{1-x}Zn_xS$ films varies from 2.41eV for CdS to 3.48eV for ZnS with x. The resistivity of the $Cd_{1-x}Zn_xS$ films increased with x.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.318.2-318.2
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• 2014

The high contact resistance is still one of the major issues to be resolved in CdS/CdTe thin film solar cells. CdTe/Metal Schottky contact induced a high contact resistance in CdS/CdTe solar cells. It has been reported that the work function of CdTe thin film is more than 5.7 eV. There has not been a suitable back contact metal, because CdTe thin film has a high work function. In a few decades, some buffer layer was reported to improve a back contact problem. Buffer layers which are Te, $Sb_2Te_3$, $Cu_2Te$, ZnTe:Cu and so on was inserted between CdTe and metal electrode. A formed buffer layers made a tunnel junction. Hole carriers which was excited in CdTe film by light absorption was transported from CdTe to back metal electrode. In this report, we reported the variation of solar cell performance with different buffer layer at the back contact of CdTe thin film solar cell.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.4
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• pp.293-297
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• 2010

We have studied the optical and electrical properties of a-IGZO thin films on the n-type semiconductor fabricated by RF magnetron sputtering method. The ceramic target was used in which $In_2O_3$, $Ga_2O_3$ and ZnO powder were mixed with 1:1:2 mol% ratio and furnished. The RF power was set at 25 W, 50 W, 75 W and 100 W as a variable process condition. The transmittance of the films in the visible range was above 80%, and it was 92% in the case of 25 W power. AFM analysis showed that the roughness increased as increasing RF power, and XRD showed amorphous structure of the films without any peak. The films are electrically characterized by high mobility above 10 $cm^2/V{\cdot}s$ at low RF power, high carrier concentration and low resistivity. It is required to study further finding the optimal process condition such as lowering the RF power, prolonging the deposition ratio and qualification analysis.

• Journal of Navigation and Port Research
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• v.26 no.1
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• pp.120-126
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• 2002

ZnS thin films were prepared on glass substrate at various deposition conditions by a HW apparatus and were systematically investigated the growth characteristics, in terms of deposition edges by a double beam spectro- photometer, and structural analysis by a x-ray diffraction rates were increased with incresing the cell temperature and vapor pressure of sulfur, but were decreased with increasing substrate temperature. The optical characteristics of thin films depends on the deposition rates. The band gap energies of 3.46∼3.52eV measured at room temperature are smaller than the theoretical value of 3.54eV, indicating that impurities exist in the crystal. All ZnS thin films are oriented in the (III) principal direction of a zincblende structure. By introducing the S vapor, optical and crystalline properties have been improved.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.527-530
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• 2009

We report on the fabrication of ZnO-based dual gate (DG) thin-film transistors (TFTs) with 20 nm-thick $Al_2O_3$ for both top and bottom dielectrics, which were deposited by atomic layer deposition on glass substrates at $200^{\circ}C$. Whether top or bottom gate is biased for sweep, our TFT almost symmetrically operates under a low voltage of 5 V showing a field mobility of ~0.4 $cm^2/V{\cdot}s$ along with the on/off ratio of $5{\times}10^4$. The threshold voltage of our DG TFT was systematically controlled from 0.5 to 2.0 V by varying counter gate input from +5 to -2 V.

• Current Photovoltaic Research
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• v.4 no.3
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• pp.114-118
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• 2016

$Cu_{1.8}Zn_{1.2}(Sn_{1-x}Ge_x)S_4$ (CZTGeS) nanocrystals were mechanochemically synthesized from elemental precursor powders without using any organic solvents and any additives. The composition of CZTGeS nanocrystals were systematically varied with different Ge mole fraction (x) from 0.1 to 0.9. The XRD, Raman spectroscopy, high-resolution TEM, and diffuse reflectance studies show that the as-synthesized CZTGeS nanocrystals exhibited consistent changes in various structural and optical properties as a function of x, such as lattice parameters, wave numbers for $A_1$ Raman vibration mode, interplanar distances (d-spacing), and optical bandgap energies. The bandgap energy of the synthesized CZTGeS nanocrystals gradually increases from 1.40 to 1.61 eV with increasing x from 0.1 to 0.9, demonstrating that Ge-doping is useful means to tune the bandgap of mechanochemically synthesized nanocrystals-based kesterite thin-film solar cells. The preliminary solar cell performance is presented with an efficiency of 3.66%.

• Korean Journal of Materials Research
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• v.18 no.7
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• pp.379-383
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• 2008

We report on the light-emitting diode (LED) characteristics of core-shell CdSe/ZnS nanocrystal quantum dots (QDs) embedded in $TiO_2$thin films on a Si substrate. A simple p-n junction could be formed when nanocrystal QDs on a p-type Si substrate were embedded in ${\sim}5\;nm$ thick $TiO_2$ thin film, which is inherently an n-type semiconductor. The $TiO_2$ thin film was deposited over QDs at $200^{\circ}C$ using plasma-enhanced metallorganic chemical vapor deposition. The LED structure of $TiO_2$/QDs/Si showed typical p-n diode currentvoltage and electroluminescence characteristics. The colloidal core-shell CdSe/ZnS QDs were synthesized via pyrolysis in the range of $220-280^{\circ}C$. Pyrolysis conditions were optimized through systematic studies as functions of synthesis temperature, reaction time, and surfactant amount.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.543-543
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• 2013

Thin-film transistors (TFTs) based on oxide semiconductors have been regarded as promising alternatives for conventional amorphous and polycrystalline silicon TFTs. Oxide TFTs have several advantages, such as low temperature processing, transparency and high field-effect mobility. Lots of oxide semiconductors for example ZnO, SnO2, In2O3, InZnO, ZnSnO, and InGaZnO etc. have been researched. Particularly, zinc-tin oxide (ZTO) is suitable for channel layer of oxide TFTs having a high mobility that Sn in ZTO can improve the carrier transport by overlapping orbital. However, some issues related to the ZTO TFT electrical performance still remain to be resolved, such as obtaining good electrical contact between source/drain (S/D) electrodes and active channel layer. In this study, the bottom-gate type ZTO TFTs with staggered structure were prepared. Thin films of ZTO (40 nm thick) were deposited by DC magnetron sputtering and performed at room temperature in an Ar atmosphere with an oxygen partial pressure of 10%. After annealing the thin films of ZTO at $400^{\circ}C$ or an hour, Cu, Mo, ITO and Ti electrodes were used for the S/D electrodes. Cu, Mo, ITO and Ti (200 nm thick) were also deposited by DC magnetron sputtering at room temperature. The channel layer and S/D electrodes were defined using a lift-off process which resulted in a fixed width W of 100 ${\mu}m$ and channel length L varied from 10 to 50 ${\mu}m$. The TFT source/drain series resistance, the intrinsic mobility (${\mu}i$), and intrinsic threshold voltage (Vi) were extracted by transmission line method (TLM) using a series of TFTs with different channel lengths. And the performances of ZTO TFTs were measured by using HP 4145B semiconductor analyzer. The results showed that the Cu S/D electrodes had a high intrinsic field effect mobility and a low effective contact resistance compared to other electrodes such as Mo, ITO and Ti.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.5
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• pp.467-475
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• 2004

ZnO epilayer were synthesized by the pulsed laser deposition(PLD) process on $Al_2$ $O_3$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(A $l_2$ $O_3$) substrate at a temperature of 400 $^{\circ}C$. The crystalline structure of epilayer was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). 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 299 $\textrm{cm}^2$/Vㆍs 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＋463k). After the as-grown ZnO epilayer was annealed in Zn atmospheres, oxygen and vaccum the origin of point defects of ZnO atmospheres has been investigated by the photoluminescence(PL) at 10 K. The native defects of $V_{Zn}$ , $V_{o}$ , Z $n_{int}$, and $O_{int}$ obtained by PL measurements were classified as a donors or accepters type. In addition, we concluded that the heat-treatment in the oxygen atmosphere converted ZnO thin films to an optical p-type. Also, we confirmed that vacuum in ZnO/A $l_2$ $O_3$did not form the native defects because vacuum in ZnO thin films existed in the form of stable bonds.s.s.s.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.114-120
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• 2012

In this research, we prepared Ga doped zinc oxide(ZnO:Ga, GZO) targets each difference sintering temperature $700^{\circ}C$, $800^{\circ}C$, and doping rate 1 wt.%, 2 wt.%, 3 wt.%. The characteristics of thin film on glass substrates which deposited by facing target sputtering in pure Ar atmosphere are reported. Ga doped zinc oxide film is attracted material through low resistivity, high transmittance, etc. When prepared target powder's structure was investigated by scanning electron microscope, densification and coarsening by driving force was observed. For each ZnO:Ga films with a $Ga_2O_3$ content of 3 wt.% at input power of 45W, the lowest resistivity of $9.967{\times}10^{-4}{\Omega}{\cdot}cm$ ($700^{\circ}C$) and $9.846{\times}10^{-4}{\Omega}{\cdot}cm$ ($800^{\circ}C$) was obtained. the carrier concentration and mobility were $4.09{\times}10^{20}cm^{-3}$($700^{\circ}C$), $4.12{\times}10^{20}cm^{-3}$($800^{\circ}C$) and $15.31cm^2/V{\cdot}s(700^{\circ}C)$, $12.51cm^2/V{\cdot}s(800^{\circ}C)$, respectively. And except 1 wt.% Ga doped ZnO thin film, average transmittance of these samples in the range 350-800 nm was over 80%.