• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.124-125
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• 2007

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 polycrystal source of $CdGa_2Se_4$ at $630^{\circ}C$ prepared from horizontal electric furnace. The photocurrent and the absorption spectra of $CdGa_2Se_4$/SI(Semi-Insulated) GaAs(100) are measured ranging from 293K 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 quasicubic 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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• 2007.11a
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• pp.167-168
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• 2007

$CdIn_2S_4$ (110) films were grown on semi-insulating GaAs (100) by a hot wall epitaxy method. Using photocurrent (PC) measurement, the PC spectra in the temperature range of 30 and 10 K appeared as three peaks in the short wavelength region. It was found that three peaks, A-, B-, and C-excitons, correspond to the intrinsic transition from the valence band states of ${\Gamma}_4(z),\;{\Gamma}_5(x),\;and\;{\Gamma}_5(y)$ to the exciton below the conduction band state of ${\Gamma}_1(s)$, respectively. The 0.122 eV crystal field splitting and the 0.017 eV spin orbit splitting were obtained. Thus, the temperature dependence of the optical band gap obtained from the PC measurement was well described by $E_g$(T)=2.7116eV - $(7.65{\times}10^{-4}\;eV/K)T^2$/(425+T). But, the behavior of the PC was different from that generally observed in other semiconductors. The PC intensities decreased with decreasing temperature. This phenomenon had ever been reported at a PC experiment on the bulk crystals grown by the Bridgman method. From the relation of log $J_{ph}$ vs 1/T, where $J_{ph}$ is the PC density, two dominant levels were observed, one at high temperatures and the other at low temperatures. Consequently, the trapping centers due to native defects in the $CdIn_2S_4$ film were suggested to be the causes of the decrease in the PC signal with decreasing temperature.

• 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.

• 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.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.3
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• pp.122-126
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• 2003

In this study, $Zn_{0.86}Mn_{0.14}$Te epilayer of 0.7 $\mu\textrm{m}$-thickness was grown on GaAs(100) substrate by using hot wallepitaxy. GaAs(100) substrate was removed from $Zn_{0.86}Mn_{0.14}$Teepilayer by the selective etching solution. The crystal structure and the lattice constant of only Z $n_{0.86}$ M $n_{0.14}$Te epilayer were investigated to be zincblende and 6.140 $\AA$ from X-ray diffraction pattern, respectively. Mn composition x of $Zn_{1-x}Mn_x$Te epilayer was found to be 0.14 using this lattice constant and Vegard's law. The crystal quality of the epilayer was confirmed to be very good due to 256 arcsec-full-width at half-maximum of the double crystal rocking curve. The absorption spectra from the transmission ones were obtained to measure the band gap energy of $Zn_{0.86}Mn_{0.14}$Te epilayer from 300 K to 10 K. With the decreasing temperature,. strong absorption regions in the absorption spectra were shifted to higher energy side and the absorption peak meaning the free exciton formation appeared near the absorption edge. The band gap energy values of $Zn_{0.86}Mn_{0.14}$Te epilayer at 0 K and 300 K were found to be almost 2.4947 eV and 2.330 eV from the temperature dependence of the free exciton peak position energy of $Zn_{0.86}Mn_{0.14}$Te epilayer, respectively. The free exciton peak position energy of $Zn_{0.86}Mn_{0.14}$Te epilayer without GaAs substrate was larger 15.4 meV than photoluminescence peak position energy at 10 K. This energy difference between two peaks was analysed to be Stokes shift.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.211-220
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• 1998

The stochiometric composition of $AgGaS_2$polycrystal source materials for the single crystal thin films were prepared from horizontal furnace. From the extrapolation method of X-ray diffraction patterns, it was found that the polycrystal $AgGaS_2$has tetragonal structure of which lattice constant $a_0\;and \;c_0$ were 5.756 $\AA$ and 10.305 $\AA$, respectively. $AgGaS_2$single crystal thin film was deposited on throughly etched GaAs(100) substrate from mixed crystal $AgGaS_2$by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $590^{\circ}C$ and $440^{\circ}C$ respectively, and the growth rate of the single crystal thin films was about 0.5 $mu \textrm{m}$/h. The crystallinity of the grown single crystal thin films was investigated by the DCRC (double crystal X-ray diffraction rocking curve). The optical energy gaps were found to be 2.61 eV for $AgGaS_2$single crystal thin films at room temperature. The temperature dependence of the photocurrent peak energy is well explained by the Varshni equation, then the constants in the Varshni equation are given by${\Alpha};=;8.695{\times}10^{-4};eV/K,and;{\beta};=;332;K$. from the photocurrent spectra by illumination of polarized light of the $AgGaS_2$single crystal thin film, we have found that crystal field splitting $\Delta$Cr was 0.28 eV at 20 K. From the PL spectra at 20 K, the peaks corresponding to free and bound excitons and a broad emission band due to D-A pairs are identified. The binding energy of the free excitons are determined to be 0.2676 eV and 0.2430 eV and the dissociation energy of the bound excitons to be 0.4695 eV.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.347-351
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• 2003

II-Ⅵ ZnO compound semiconductor thin films were grown on $\alpha$-Al$_2$O$_3$(0001) single crystal substrate by radical beam assisted molecular beam epitaxy and the optical properties were investigated. Zn(6N) was evaporated using Knudsen cell and O radical was assisted at the partial pressure of 1$\times$10$^{4}$ Torr and radical beam source of 250-450 W RF power. In $\theta$-2$\theta$ x-ray diffraction analysis, ZnO thin film with 500 nm thickness showed only ZnO(0002)and ZnO(0004) peaks is believed to be well grown along c-axis orientation. Photoluminescence (PL) measurement using He-Cd ($\lambda$=325 nm) laser is obtained in the temperature range of 9 K-300 K. At 9 K and 300 K, only near band edge (NBE) is observed and the FWHM's of PL peak of the ZnO deposited at 450 RF power are 45 meV and 145 meV respectively. From no observation of any weak deep level peak even at room temperature PL, the ZnO grains are regarded to contain very low defect density and impurity to cause the deep-level defects. The peak position of free exciton showed slightly red-shift as temperature was increased, and from this result the binding energy of free exciton can be experimentally determined as much as $58\pm$0.5 meV, which is very closed to that of ZnO bulk. By van der Pauw 4-point probe measurement, the grown ZnO is proved to be n-type with the electron concentration($n_{e}$ ) $1.69$\times$10^{18}$$cm^3$, mobility($\mu$) $-12.3\textrm{cm}^2$/Vㆍs, and resistivity($\rho$) 0.30 $\Omega$$\cdot$cm.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.81-81
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• 2003

The stochiometric mixture of evaporating materials for the CuGaSe$_2$ single crystal thin films were prepared from horizontal furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal CuGaSe$_2$, it was found tetragonal structure whose lattice constant no and co were 5.615$\AA$ and 11.025$\AA$, respectively. To obtains the single crystal thin films, CuGaSe$_2$ mixed crystal was deposited on throughly etched GaAs(100) by the Hot Wall Epitaxy(HWE) system. The source and substrate temperature were 61$0^{\circ}C$ and 45$0^{\circ}C$ respectively, and the growth rate of the single crystal thin films was about 0.5${\mu}{\textrm}{m}$/h. The crystalline structure of single crystal thin films was investigated by the double crystal X-ray diffraction(DCXD). Hall effect on this sample was measured by the method of van der pauw and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by pizoelectric scattering in the temperature range 30K to 150K and by polar optical scattering in the temperature range 150K to 293K. The optical energy gaps were found to be 1.68eV for CuGaSe$_2$ single crystal thin films at room temperature. The temperature dependence of the photocurrent peak energy is well explained by the Varshni equation then the constants in the Varshni equation are given by a=9.615$\times$ 10$^{-4}$ eV/K, and $\beta$=335K. From the photocurrent spectra by illumination of polarized light of the CuGaSe$_2$ single crystal thin films. We have found that values of spin orbit coupling ΔSo and crystal field splitting ΔCr was 0.0900eV and 0.2498eV, respectively. From the PL spectra at 20K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0626eV and the dissipation energy of the acceptor-bound exciton and donor-bound exciton to be 0.0352eV, 0.0932eV, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.11
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• pp.848-853
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• 2010

We have grown GaN nanowires by the low pressure MOCVD method on Ni deposited oxidized Si surface and have established optimum conditions by observing surface microstructure and its photoluminescence. Optimum growth temperature of $880^{\circ}C$, growth time of 30 min, TMG source flow rate of 10 sccm have resulted in dense nanowires on the surface, however further increase of growth time or TMG flow rate has not increased the length of nanowire but has formed nanocrystals. On the contrary, the increase of ammonia flow has increased the length of nanowires and the coverage of nanowire over the surface. The shape of nanowire is needle-like with a Ni droplet at its tip; the length is tens of micron with more than 40 nm in diameter. Low temperature photoluminescence obtained from the sample at optimum growth condition has revealed several peaks related to exciton decay near band-edge, but does not show any characteristic originated from one dimensional quantum confinement. Strong and broad luminescence at 2.2 eV is observed from dense nanowire samples and this suggests that the broad band is related to e-h recombination at the surface state in a nanowire. The current result is implemented to the nanowire device fabrication by nanowire bridging between micro-patterned neighboring Ni catalysis islands.

• Applied Science and Convergence Technology
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• v.27 no.5
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• pp.95-99
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• 2018

We discuss the structural and optical characteristics of GaN nanowires (NWs) grown on Si(111) substrates by a plasma-assisted molecular-beam epitaxy. The GaN NWs with high crystal quality were formed by adopting a new growth approach, so called Ga pre-deposition (GaPD) method. In the GaPD, only Ga was supplied without nitrogen flux on a SiN/Si surface, resulting in the formation of Ga droplets. The Ga droplets were used as initial nucleation sites for the growth of GaN NWs. The GaN NWs with the average heights of 60.10 to 214.62 nm obtained by increasing growth time. The hexagonal-shaped top surfaces and facets were observed from the field-emission electron microscope images of GaN NWs, indicating that the NWs have the wurtzite (WZ) crystal structure. Strong peaks of GaN (0002) corresponding to WZ structures were also observed from double crystal x-ray diffraction rocking curves of the NW samples. At room temperature, free-exciton emissions were observed from GaN NWs with narrow linewidth broadenings, indicating to the formation of high-quality NWs.