• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.283-290
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• 2013

A stoichiometric mixture of evaporating materials for $MgGa_2Se_4$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $MgGa_2Se_4$ 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 $610^{\circ}C$ and $400^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the $MgGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=2.34 eV-(8.81{\times}10^{-4}eV/K)T^2/(T+251K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $MgGa_2Se_4$ have been estimated to be 190.6 meV and 118.8 meV, 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 $MgGa_2Se_4$/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1^-}$, $B_{1^-}$exciton for n = 1 and $C_{27}-exciton$ peaks for n = 27.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.287.1-287.1
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• 2016

Three-dimensional (3-D) semiconductor nanoarchitectures, including nano- and micro- rods, pyramids, and disks, are emerging as one of the most promising elements for future optoelectronic devices. Since these 3-D semiconductor nanoarchitectures have many interesting unconventional properties, including the use of large light-emitting surface area and semipolar/nonpolar nano- or micro-facets, numerous studies reported on novel device applications of these 3-D nanoarchitectures. In particular, 3-D nanoarchitecture devices can have noticeably different current spreading characteristics compared with conventional thin film devices, due to their elaborate 3-D geometry. Utilizing this feature in a highly controlled manner, color-tunable light-emitting diodes (LEDs) were demonstrated by controlling the spatial distribution of current density over the multifaceted GaN LEDs. Meanwhile, for the fabrication of high brightness, single color emitting LEDs or laser diodes, uniform and high density of electrical current must be injected into the entire active layers of the nanoarchitecture devices. Here, we report on a new device structure to inject uniform and high density of electrical current through the 3-D semiconductor nanoarchitecture LEDs using metal core inside microtube LEDs. In this work, we report the fabrications and characteristics of metal-cored coaxial $GaN/In_xGa_{1-x}N$ microtube LEDs. For the fabrication of metal-cored microtube LEDs, $GaN/In_xGa_{1-x}N/ZnO$ coaxial microtube LED arrays grown on an n-GaN/c-Al2O3 substrate were lifted-off from the substrate by wet chemical etching of sacrificial ZnO microtubes and $SiO_2$ layer. The chemically lifted-off layer of LEDs were then stamped upside down on another supporting substrates. Subsequently, Ti/Au and indium tin oxide were deposited on the inner shells of microtubes, forming n-type electrodes of the metal-cored LEDs. The device characteristics were investigated measuring electroluminescence and current-voltage characteristic curves and analyzed by computational modeling of current spreading characteristics.

• New Physics: Sae Mulli
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• v.68 no.12
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• pp.1281-1287
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• 2018

In this study, $Al_xGa_{1-x}N$ films were grown on (0001) sapphire substrates by using metal-organic chemical vapor deposition (MOCVD). The crystallinity of the grown films was examined with X-ray diffraction (XRD) patterns. The surfaces and the chemical properties of the $Al_xGa_{1-x}N$ films were investigated using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The optical properties of the $Al_xGa_{1-x}N$ film were studied in a wide photon energy range between 2.0 ~ 8.7 eV by using spectroscopic ellipsometry (SE) at room temperature. The data obtained by using SE were analyzed to find the critical points of the pseudodielectric function spectra, $<{\varepsilon}(E)>=<{\varepsilon}_1(E)>+i<{\varepsilon}_2(E)>$. In addition, the second derivative spectra, $d^2<{\varepsilon}(E)>/dE^2$, of the pseudodielectric function for the $Al_xGa_{1-x}N$ films were numerically calculated to determine the critical points (CPs), such as the $E_0$, $E_1$, and $E_2$ structure. For the four samples (x = 0.18, 0.21, 0.25, 0.29) between a composition of x = 0.18 and x = 0.29, changes in the critical points (blue-shifts) with increasing Al composition at 300 K for the $Al_xGa_{1-x}N$ film were observed via ellipsometric measurements for the first time.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.7
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• pp.624-630
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• 2006

ZnO deposition parameters are not independent and have a nonlinear and complex property. To propose a method that could verify and predict the relations of process variables, neural network was used. At first, ZnO thin films were deposited by using RF magnetron sputtering process with various conditions. Si, GaAs, and Glass were used as substrates. The temperature, work pressure, and RF power of the substrate were $50\sim500^{\circ}C$, 15 mTorr, and $180\sim210W$, respectively : the purity of the target was ZnO 4 N. Structural properties of ZnO thin films were estimated by using XRD (0002) peak intensity. The structure of neural network was a form of 4-7-1 that have one hidden layer. In training a network, learning rate and momentum were selected as 0.2, 0.6 respectively. A backpropagation neural network were performed with XRD (0002) peak data. After training a network, the temperature of substrate was evaluated as the most important parameter by sensitivity analysis and response surface. As a result, neural network could capture nonlinear and complex relationships between process parameters and predict structural properties of ZnO thin films with a limited set of experiments.

• Current Photovoltaic Research
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• v.3 no.2
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• pp.54-60
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• 2015

ZnSnO thin films were deposited by atomic layer deposition (ALD) process using diethyl zinc ($Zn(C_2H_5)_2$) and tetrakis (dimethylamino) tin ($Sn(C_2H_6N)_4$) as metal precursors and water vapor as a reactant. ALD process has several advantages over other deposition methods such as precise thickness control, good conformality, and good uniformity for large area. The composition of ZnSnO thin films was controlled by varying the ratio of ZnO and $SnO_2$ ALD cycles. The ALD ZnSnO film was an amorphous state. The band gap of ZnSnO thin films increased as the Sn content increased. The CIGS solar cell using ZnSnO buffer layer showed about 18% energy conversion efficiency. With such a high efficiency with the ALD ZnSnO buffer and no light soaking effect, AlD ZnSnO buffer mighty be a good candidate to replace Zn(S,O) buffer in CIGSsolar cells.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.79-80
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• 2006

A stoichiometric mixture of evaporating materials for $CdIn_2S_4$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CdIn_2S_4$ mixed crystal was deposited on thoroughly etched semi-Insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The temperature dependence of the energy band gap of the $CdIn_2S_4$ obtained from the absorption spectra was well described by the Varshni's relation. $E_g(T)=2.7116 eV-(7.74{\times}10^{-4} eV)T^2/(T+434)$. The crystal field and the spin-orbit splitting energies for the valence band of the $CdIn_2S_4$ have been estimated to be 0.1291 eV and 0.0248 eV, 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 $AgInS_2$/GaAs epilayer. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and C1-exciton peaks for n = 1.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.111-112
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• 2005

To obtain the single crystal thin films, $CuInSe_2$, mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wail epitaxy (HWE) system. The source and substrate temperatures were 620$^{\circ}C$ 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 mobilily of $CuInSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.62\times10^{16}$ $cm^{-3}$ and $296cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the CulnSe$_2$ obtained from the absorption spectra was well described by the Varshni's relation E$_g$(T) = 1.1851 eV - ($8.99\times10^{-4}$ ev/K)T$_2$/(T + 153K). After the as-grown $CuInSe_2$ single crystal thin films was annealed in Cu-, Se-, and In-atmospheres the origin of point defects of $CuInSe_2$ single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The nat ive defects of V$_{Cu}$, $V_{Se}$, Cu$_{int}$, and $Se_{int}$ obtained by PL measurements were classified as a donors or accepters type. And we concluded that the heat-treatment in the Cu-atmosphere converted $CuInSe_2$ single crystal thin films to an optical n-type. Also, we confirmed that In in $CuInSe_2$/GaAs did not form the native defects because In in $CuInSe_2$ single crystal thin films existed in the form of stable bonds.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.164-164
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• 2003

UV 발광소자 재료로서 유망한 ZnO film을 ALE법으로 증착하고 photoluminescence특성을 조사하였다. Zn소스로서 DEZn(Diethylzinc)를, 산소 소스로서 DI water를 사용하였고 $N_2$ gas로서 챔버내에 주입된 소스물질을 purge하였다. ALE 공정온도 범위인 17$0^{\circ}C$와 CVD 반응온도 범위인 40$0^{\circ}C$로 ZnO 박막을 증착하고 이 시편을 산소 분위기에서 600-100$0^{\circ}C$의 온도로 1시간 동안 열처리하였다. 그리고 He-Cd laser를 사용하여 photoluminescence를 측정하였다. 17$0^{\circ}C$와 40$0^{\circ}C$ 에서 증착된 시편 모두 as-grown 상태에서는 거의 발광특성을 나타내지 못하였으나 후열처리를 거치면서 발광특성을 나타내었고 열처리 온도가 높을수록 발광강도가 증가하였다. 40$0^{\circ}C$에서의 증착된 시편의 경우는CVD반응이 발생하여 Zn-Zn결합이 많이 생성되어 열처리 온도가 증가하여도 발광강도가 약하였고 가시광 영역의 발광 또한 크게 증가하였으며 17$0^{\circ}C$에서 증착된 시편의 경우는 열처리 온도가 증가할수록 UV영역의 발광강도만이 크게 증가하였으며 가시광 영역의 발광은 거의 증가하지 않았다.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.234-238
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• 2004

A stoichiometric mixture of evaporating materials for $CuInSe_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CuInSe_2$ 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 $620^{\circ}C$ 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 $CuInSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.62{\times}10^{l6}\;cm^{-3}$ and $296\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuInSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;=\;1.1851\;eV\;-\;(8.99{\times}10^{-4}\;eV/K)T^2/(T+153K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $CuInSe_2$ have been estimated to be 0.0087 eV and 0.2329 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 $\Gamma_6$ states of the valence band of the $CuInSe_2$. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.