• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.280.1-280.1
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• 2016

Generally InGaN/GaN green light emitting diode (LED) exhibits the low quantum efficiency (QE) due to the large lattice mismatch between InGaN and GaN. The QE of InGaN-based multiple quantum wells (MQWs) is drastically decreased when an emission wavelength shifts from blue to green wavelength, so called "green gap". The "green gap" has been explained by quantum confined Stark effect (QCSE) caused by a large lattice mismatch. In order to improve the QE of green LED, undoped graded short-period InGaN/GaN superlattice (GSL) and Si-doped GSL (SiGSL) structures below the 5-period InGaN/GaN MQWs were grown on the patterned sapphire substrates. The luminescence properties of InGaN/GaN green LEDs have been investigated by using photoluminescence (PL) and time-resolved PL (TRPL) measurements. The PL intensity of SiGSL sample measured at 10 K shows stronger about 1.3 times compared to that of undoped GSL sample, and the PL peak wavelength at 10 K appears at 532 and 525 nm for SiGSL and undoped GSL, respectively. Furthermore, the PL decay of SiGSL measured at 10 K becomes faster than that of undoped GSL. The faster decay for SiGSL is attributed to the increased wavefunction overlap between electron and hole due to the screening of piezoelectric field by doped carriers. These PL and TRPL results indicate that the QE of InGaN/GaN green LED with GSL structure can be improved by Si-doping.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.160-160
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• 2010

In this work, we investigate ohmic contacts to p-type GaN using a Pt/Cu/Au metallization scheme in order to achieve low resistance and thermally stable ohmic contact on p-GaN. An ohmic contact formed by a metal electrode deposited on a highly doped InGaN/GaN superlattice sturucture on p-GaN layer. The specific contact resistance is $1.56{\times}10^{-6}{\Omega}cm^2$ for the as-deposited sample, $1.35{\times}10^{-4}{\Omega}cm^2$ for the sample annealed at $250^{\circ}C$ and $6.88{\times}10^{-3}{\Omega}cm^2$ for the sample annealed at $300^{\circ}C$.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1069-1074
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• 2008

In this work, we made a study for the 3D SAM formation of octanethiol, decanethiol, and dodecanethiol on copper nanoparticles and we verified stability of the copper particle depending on the ratio of dodecanethiol to copper. The reaction was performed in a one-phase system under nitrogen atmosphere and the thiolated copper particles could be obtained by centrifugation. We could confirm that the nanoparticles consisted of a spherical shape of 3~6 nm from TEM images. FT-IR, XPS and TGA results showed that alkanethiols were chemisorbed via thiol group and the packing density of the alkanethiols on copper surface increased with the alkyl chain lengths. XRD patterns gave us useful information about superlattice formations. Finally, $Cu_2O$ was formed when the molar ratio of dodecanethiol to copper is less than unity and copper nanoparticles formed more compact 3D SAMs when the molar ratio of dodecanethiol to copper was 1.25.

• Journal of the Korean Magnetics Society
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• v.3 no.4
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• pp.305-309
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• 1993

Thermal stability of Co/Cu artificial superlattice (AS) prepared by RF-magnetron sputtering and the effect of low temperature annealing on the magnetoresistance of the AS have been investigated in this work. Dependence of annealing behavior on the Cu spacer thickness, Fe underlayer thickness, and kind of the underlayer was examined and the relationship between the interfacial reaction and magnetoresistance was studied. It turned out that when Co/Cu AS was annealed at low temperature ($<450^{\circ}C$), the magnetoresistance could increase in the case of AS with thick spacer Cu ($20~25\AA$) layer, whereas it decreased in the case of AS with thin spacer Cu ($7\AA$) layer, which of the former is in contrast with previous reports and the latter in consistent with them. The increase of magnetoresistance is due to increase of interfacial atomic sharpness, which is supported by low angle X-ray diffraction analysis. The thermal stability of Co/Cu AS was better in the case of thick Fe underlayered AS. Interfacial reaction (separation of intermixed Co and Cu) could be observed at lower temperature for (200)-textured samples than for (111)-textured samples, which can be interpreted in terms of interdiffusion kinetics depending on the crystallographic orientation.

• ETRI Journal
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• v.21 no.1
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• pp.1-27
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• 1999

We present a new description of envelope-function equation of the superlattice (SL). The SL wave function and corresponding effective-mass equation are formulated in terms of a linear combination of Bloch states of the constituent material with smaller band gap. In this envelope-function formalism, we review the fundamental concept on the motion of a wave packet in the SL structure subjected to steady and uniform electric fields F. The review confirms that the average of SL crystal momentums K = ($k_x,k_y,q$), where ($K_x,k_y$) are bulk inplane wave vectors and q SL wave vector, included in a wave packet satisfies the equation of motion = $_0+Ft/h$; and that the velocity and acceleration theorems provide the same type of group velocity and definition of the effective mass tensor, respectively, as in the Bulk. Finally, Schlosser and Marcus's method for the band theory of metals has been by Altarelli to include the interface-matching condition in the variational calculation for the SL structure in the multi-band envelope-function approximation. We re-examine this procedure more thoroughly and present variational equations in both general and reduced forms for SLs, which agrees in form with the proposed envelope-function formalism. As an illustration of the application of the present work and also for a brief investigation of effects of band-parameter difference on the subband energy structure, we calculate by the proposed variational method energies of non-strained $GaAs/Al_{0.32}Ga_{0.68}As$ and strained $In_{0.63}Ga_{0.37}As/In_{0.73}Ga_{0.27}As_{0.58}P_{0.42}SLs$ with well/barrier widths of $60{\AA}/500{\AA}$ and 30${\AA}/30{\AA}$, respectively.

• Journal of the Korean Ceramic Society
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• v.56 no.1
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• pp.49-55
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• 2019

$Ti_{0.33}Al_{0.67}N/CrN$ nano-multilayers, which are known to have excellent wear resistance, were prepared using an unbalanced magnetron sputter to have various periods of 2-5 nm. $Ti_{0.33}Al_{0.67}N$ had a hexagonal structure in a single layer, but converted to a cubic structure by forming a multilayer with CrN, which has a cubic structure. Thus, $Ti_{0.33}Al_{0.67}N$ formed a superlattice in the multilayer. The $Ti_{0.33}Al_{0.67}/CrN$ multilayer with a period of 2.5 nm greatly exceeded the hardness of the $Ti_{0.33}Al_{0.67}N$ and the CrN single layer, reaching 39 GPa. According to the low angle X-ray diffraction results, the $Ti_{0.33}Al_{0.67}N/CrN$ multilayer maintained its as-coated structure to a temperature as high as $700^{\circ}C$ and exhibited hardness of 30 GPa. The thickness of the oxide layer of the $Ti_{0.33}Al_{0.67}N/CrN$ multilayered coating was less than one-tenth of those of the single layers. Thus, $Ti_{0.33}Al_{0.67}N/CrN$ multilayered coating had hardness and oxidation resistance far superior to those of its constituent single layers.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.395-395
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• 2012

We fabricate organic-inorganic hybrid thin film for the purpose of encapsulation by molecular layer deposition (MLD) using Trimethylaluminium (TMA) and Adipoyl Chloride (AC). Ellipsometry was employed to verify self limiting reaction of ALD. Linear relationship between number of cycle and thickness was obtained. We found that desirable organic thin film fabrication is possible by MLD surface reaction in nanoscale. Purging was carried out after dosing of each precursor to form monolayer in each sequence. We also confirmed roughness of the organic thin film by atomic force microscopy. We deposit TMA and AC at $70^{\circ}C$ and that 1.78A root mean square was obtained which indicates that uniform organic thin film was formed. We confirmed precursor's functional group by IR spectrum. We calculated WVTR of organic-inorganic hybrid super-lattice epitaxial layer using Ca test. WVTR indicates superlattice film can be possibly use as encapsulation in flexible devices.

• Korean Journal of Materials Research
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• v.7 no.10
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• pp.914-918
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• 1997

MBS에 의해(001)GaAs기판 위에 성장된 Zn$_{1-x}$Co$_{x}$Se(x=1.0, 7.4, 9.5 %)반도체 박막과 (ZnSe/FeSe)반도체 초격자 박막의 미세구조를 투과전자현미경을 이용하여 연구하였다. Zn$_{1-x}$Co$_{x}$Se 박막 시편의 경우, 박막과 기판 사이의 격자 불일치때문에 a/2<110>형태의 버거즈 벡터를 가지는 부정합 전위를 관찰하였다. 모든 Zn$_{1-x}$Co$_{x}$Se 박막과 기판의 계면은 뚜렷이 구별되었고, 계면에서 산화물이나 이물질이 존재하지 않았다. 또한, (ZnSe/FeSe)초격자를 성장시키기 전에 GaAs기판 위에 ZnSe바닥층을 넣음으로써 고품질의 (ZnSe/FeSe)초격자를 얻었다. (ZnSe/FeSe)초격자에 있는 FeSe는 섬아연광 결정구조로 존재하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.38-38
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• 2003

PTO/PZO 초격자 박막은 박막 계면에 응력이 발생하여 기존의 박막처럼 size effect가 적용되지 않고 두께가 감소해도 높은 유전상수를 갖는다. Antiferroelectric PbZrO$_3$(PZO)와 ferroelectric PbTiO$_3$(PTO)를 적층 성장시킨 초격자는 400도에서 성장한 (100) Pt/SiO$_2$기판 위에 rf magnetron sputtering으로 증착하였다. PTO/PZO의 증착 주기는 30(PTO $_{4unti cells}$/PZO $_{4unti cells}$) 에서 1(PTO $_{125unti cells}$/PZO $_{125unti cells}$)까지 두께의 변화를 주어 준비했고 초격자 박막의 전체두께는 100nm로 고정시켰다. XRD결과, PTO/PZO는 주기에 따라 초격자의 특성인 main peak과 satellite peak을 관찰 할 수 있었다. 초격자의 주기가 감소함에 따라 2$\theta$값이 증가하고 평균 d 값이 감소되면서 PTO층에 뒤틀림이 증가하였다. PTO층의 뒤틀림 증가로 인해 superlattice의 주기가 증가함에 따라 초격자의 유전율이 증가하였고 강유전성이 향상되었다.향상되었다.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.1
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• pp.33-41
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• 2003

The optical properties of $ZnS_ySe_{1-\chi-y}:Te_{\chi}(\chi<0.08,y~0.11)$ alloys grown by molecular beam epitaxy (MBE) have been investigated by photoluminescence (PL) and PL-excitation (PLE) spectroscopy. Good optical properties and high crystal quality were established with lattice match condition to GaAs substrate. At room temperature, emission in the visible spectrum region from blue to green was obtained by varying the Te content of the ZnSSe:Te alloy. The efficient blue and green emission were assigned to $Te_1 and Te_n(n\geq2)$cluster bound excitons, respectively. Bright green (535 nm) and blue (462 nm) light emitting diodes (LEDs) have been developed using ZnSSe:Te system as an active layer. The turn-on voltage of 2.1 V in current-voltage characteristics is very small compared to that of commercial InGaN-based LEDs (>3.4 V), indicating the formation of a good ohmic contact due to the optimized p-ZnSe/p-ZnTe multi-quantum well (MQW) superlattice electrode layers.