• 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 Magnetics
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• v.19 no.2
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• pp.126-129
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• 2014

We report the crystallographic and magnetic properties of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ by means of X-ray diffractometer (XRD), a superconducting quantum interference device (SQUID) magnetometer, and a M$\ddot{o}$ssbauer spectroscopy. In particular, $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was studied by M$\ddot{o}$ssbauer analysis for evidence of spin reorientation. The chalcogenide material $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was fabricated by a direct reaction method. XRD analysis confirmed that $Ni_{0.3}Fe_{0.7}Ga_2S_4$ has a 2-dimension (2-D) triangular lattice structure, with space group P-3m1. The M$\ddot{o}$ssbauer spectra of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ at spectra at various temperatures from 4.2 to 300 K showed that the spectrum at 4.2 K has a severely distorted 8-line shape, as spin liquid. Electric quadrupole splitting, $E_Q$ has anomalous two-points of temperature dependence of $E_Q$ curve as freezing temperature, $T_f=11K$, and N$\acute{e}$el temperature, $T_N=26K$. This suggests that there appears to be a slowly-fluctuating "spin gel" state between $T_f$ and $T_N$, caused by non-paramagnetic spin state below $T_N$. This comes from charge re-distribution due to spin-orientation above $T_f$, and $T_N$, due to the changing $E_Q$ at various temperatures. Isomer shift value ($0.7mm/s{\leq}{\delta}{\leq}0.9mm/s$) shows that the charge states are ferrous ($Fe^{2+}$), for all temperature range. The Debye temperature for the octahedral site was found to be ${\Theta}_D=260K$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.121-124
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• 2012

The characteristics of Ga-doped zinc oxide (GZO) thin films deposited at different deposition temperatures (TS~250 to $550^{\circ}C$) on 4H-SiC have been investigated. Structural and electrical properties of GZO thin film on n-type 4H-SiC(0001) were investigated by using x-ray diffraction(XRD), atomic force microscopy(AFM), Hall effect measurement, barrier height from I-V curve and Auger electron spectroscopy(AES). XRD $2\theta$ scan shows GZO thin film has preferential orientation with c-axis perpendicular to SiC substrate surface. The lowest resistivity ($\sim1.9{\times}10^{-4}{\Omega}cm$) was observed for the GZO thin film deposited at $400^{\circ}C$. As deposition temperature increases, barrier height between GZO and SiC was increased. Whereas, resistivity of GZO thin films as well as barrier height between GZO and SiC were increased after annealing process in air atmosphere. It has been found that the c-axis oriented crystalline quality as well as the relative amount of activated Ga3+ ions and oxygen vacancy may affect the electrical properties of GZO films on SiC.

• Current Optics and Photonics
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• v.1 no.4
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• pp.358-363
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• 2017

In this study, we present a detailed investigation of luminescence properties of a blue light-emitting diode using InGaN/GaN (indium component is 17.43%) multiple quantum wells as the active region grown on patterned sapphire substrate by low-pressure metal-organic chemical vapor deposition (MOCVD). High-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman scattering (RS) and photoluminescence (PL) measurements are employed to study the crystal quality, the threading dislocation density, surface morphology, residual strain existing in the active region and optical properties. We conclude that the crystalline quality and surface morphology can be greatly improved, the red-shift of peak wavelength is eliminated and the superior blue light LED can be obtained because the residual strain that existed in the active region can be relaxed when the LED is grown on patterned sapphire substrate (PSS). We discuss the mechanisms of growing on PSS to enhance the superior luminescence properties of blue light LED from the viewpoint of residual strain in the active region.

• Journal of the Korean Vacuum Society
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• v.8 no.4A
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• pp.445-449
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• 1999

We studied the properties of the InAs epitaxial layers grown of (100)-oriented GaAs ($2^{\circ}$tilted toward[011]) by molecular beam epitaxy. From DCX (double-crystal x0ray), the better crystal quality was shown in InAs epitaxial layers on about 2500$\AA$ GaAs epitaxial layers on GaAs, we obtained the high mobility of InAs epitaxy in As/In BEP ratio (1.2~2.0) from Hall effect measurement. The electron mobility increased as electron concentration increases, until Si cell temperature $960^{\circ}C$$(N_D=2.21\times10^{-17}\textrm{cm}^{-3})$. The mobility decreases as the Si cell temperature increases, at the temperature over $960^{\circ}C$. We obtained the high mobility (1.10$\times$104cm2/V.s) at Si electron concentration of $N_D=2.21\times10^{-17}\textrm{cm}^{-3}$.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.92-92
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• 1999

양자우물 무질서화 기술은 양자우물구조의 성장후 그 구조의 밴드갭을 국부적으로 변화시킬 수 있는 기술적 특성으로 인해 기존의 광기능 소자 제작을 위한 결정재성장방법을 대체 혹은 보완할 수 있는 장점이 있기 때문에 최근 활발히 연구되고 있다. 여러 가지 양자우물 무질서화공정중 유전체 박막을 사용하는 impurity free vacancy disordering (IFVD) 공정은 불순물이 개입하지 않는 공정으로 공정후 양질의 반도체 표면을 유지할 수 있는 장점이 있으며 고아소자 제작시 광손실의 증가를 초래하지 않는다. 이 공정은 vacancy의 source로 작용하는 유전체박막의 특성에 크게 의존하며 GaAs/AlGaAs 계열의 양자우물에서는 많은 연구가 진행되었으나, 광통신용 광소자의 제작에 사용되는 InGaAs/InGaAsP 계열의 양자우물에 대한 연구는 충분하지 않다. 그림 1은 IFVD를 위해 본 연구에서 사용된 CBE로 성장한 InGaAs/InGaAsP SQW 구조이다. 성장된 구조는 상온에서의 QW peak, λpl=1550nm 이었다. IFVD를 위한 유전체 덮개층으로는 PECVD로 성장 조정하여 박막성장시의 조건을 변화시킴으로써 유전체 덮개층 박막의 특성을 변화시켰다. 그림 2는 질소 분위기의 furnace에서 75$0^{\circ}C$로 8분간 IFVD를 수행한후 측정한 무질서화된 양자우물의 상온 PL spectrum을 보여준다. 그림에서 보는바와 같이 동일한 SiNx 덮개층을 사용하는 경우에도 적어도 24meV의 bandgap차를 갖는 양자우물을 영역을 동일한 기판상에 제작할 수 있음을 알 수 있다. 일반적으로 IFVD 방법으로 국부적으로 양자우물을 무질서화 하기 위해서는 SiNx/SiO2와 같은 강이한 박막을 사용하였지만 이 방법을 사용하는 경우 상이한 박막을 사용하는 데서 야기되는 제반 문제를 해결할 수 있을 것으로 판단된다. 따라서 이 기술은 기존의 광소자 제작을 위한 IFVD 방법의 문제점을 해결할 뿐만 아니라 결정 재성장 없이 도일한 기판상에 국부적으로 상이한 bandgap 영역을 만들 수 있기 때문에 광소자 제작에 적극 이용될 수 있다.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.1-11
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• 2005

The stoichiometric mixture of evaporating materials for the $CuInSe_2$ single crystal thin film was prepared from horizontal furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal $CuInSe_2$, it was found tetragonal structure whose lattice constant $a_0$ and $c_0$ were $5.783\;{\AA}$ and $11.621\;{\AA}$, respectively. To obtain the $CuInSe_2$ single crystal thin film, $CuInSe_2$ mixed crystal was deposited on throughly etched GaAs(100) by the HWE(Hot Wall Epitaxy) system. The source and substrate temperature were $620^{\circ}C$ and $410^{\circ}C$ respectively. The crystalline structure of $CuInSe_2$ single crystal thin film 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 impurity scattering in the temperature range 30 K to 100 K and by lattice scattering in the temperature range 100 K to 293 K. 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, $E_g(T)=1.1851\;eV-(8.99{\times}10^{-4}\;eV/K)T^2/(T+153\;K)$. The open-circuit voltage, short current density, fill factor, and conversion efficiency of $n-CdS/p-CuGaSe_2$ heterojunction solar cells under $80\;mW/cm^2$ illumination were found to be 0.51V, $29.3\;mA/cm^2$, 0.76 and 14.3 %, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.70-75
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• 1997

An improved technique based upon an electron beam evaporation system has been developed to prepare cubic thin films In crystalline semiconductors. Zinc blonde CdSe epilayers were grown on GaAs(100) substrate by an e-beam evaporation method. The lattice parameter obtained from (400) reflection is $6.077\AA$, which is in excellent agreement with the value reported in the literature for zinc blonde CdSe. The orientation of the as-grown CdSe epilayer is determined by electron channeling patterns. The crystallinity of epitaxial CdSe layers were investigated on the double crystal X-ray rocking curve. The carrier concentration and mobility of epilayers deduced by Hall effect measurement are about $10^{18}{\textrm}{cm}^{-3}$, $10^2\textrm{cm}^2/V{\cdot}sec$ at room temperature, respectively. The photocurrent spectrum peak of the epilayer at 30 K exhibits a sharp change at 1.746 eV due to the free exciton of cubic CdSe.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.153-153
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• 2010

Recently, to develop GaN-based light-emitting diodes (LEDs) with better performances, various approaches have been suggested by many research groups. In particular, using the patterned sapphire substrate technique has shown the improvement in both internal quantum efficiency and light extraction properties of GaN-based LEDs. In this paper, we discuss the influences of the direction of the hexagonal-structure arrays of lens-shaped patterns (HSAPs) formed on sapphire substrates on the crystal, optical, and electrical properties of InGaN/GaN multi-quantum-well (MQW) LEDs. The basic direction of the HSAPs is normal (HSAPN) with respect to the primary flat zone of a c-plane sapphire substrate. Another HSAP tilted by 30o (HSAP30) from the HSAPN structure was used to investigate the effects of the pattern direction. The full width at half maximums (FWHMs) of the double-crystal x-ray diffraction (DCXRD) spectrum for the (0002) and (1-102) planes of the HSAPN are 320.4 and 381.6 arcsecs., respectively, which are relatively narrower compared to those of the HSP30. The photoluminescence intensity for the HSAPN structure was ~1.2 times stronger than that for the HSAP30. From the electroluminescence (EL) measurements, the intensity for both structures are almost similar. In addition, the effects of the area of the individual lens pattern consisting of the hexagonal-structure arrays are discussed using the concept of the planar area fraction (PAF) defined as the following equation; PAF = [1-(patterns area/total unit areas)] For the relatively small PAF region up to 0.494, the influences of the HSAP direction on the LED characteristics were significant. However, the direction effects of the HSAP became small with increasing the PAF.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.1
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• pp.1-9
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• 2005

A stoichiometric mixture of evaporating materials for AgGaS₂ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, AgGaS₂ 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 590℃ and 440℃, respectively. The temperature dependence of the energy band gap of the AgGaS₂ obtained from the absorption spectra was well described by the Varshni's relation, E/sub g/(T) = 2.7284 eV - (8.695×10/sup -4/ eV/K)T²/(T + 332 K). After the as-grown AgGaS₂ single crystal thin films was annealed in Ag-, S-, and Ga-atmospheres, the origin of point defects of AgGaS₂ single crystal thin films has been investigated by the photoluminescence (PL) at 10 K. The native defects of V/sub Ag/, V/sub s/, Ag/sub int/, and S/sub int/ obtained by PL measurements were classified as a donors or accepters type. And we concluded that the heat-treatment in the Ag-atmosphere converted AgGaS₂ single crystal thin films to an optical n-type. Also, we confirmed that Ga in AgGaS₂/GaAs crystal thin films did not form the native defects because Ga in AgGaS₂ single crystal thin films existed in the form of stable bonds.