• Title, Summary, Keyword: Superlattice

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Effect of Interface Roughness on Magnetoresistance of[Ni/Mn] Superlattice-Based Spin Valves

  • J.R. Rhee;Kim, M.Y.;J.Y. Hwang;Lee, S.S.
    • Journal of Magnetics
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    • v.6 no.4
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    • pp.145-147
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    • 2001
  • The effect of interface roughness between [Ni/Mn] superlattice and pinned NiFe layer on magnetoresistance (MR) of [Ni/Mn] superlattice-based spin valve films was investigated. Antiferromagnetic phase structure and interface roughness of [Ni/Mn] superlattice spin valve films were compared in the as-deposited and the annealed samples at 240$\^{C}$, respectively. Surface morphology of spin valves was substantially flattened due to the formation of the antiferromatic NiMn phase. In case of Co insertion between Cu and NiFe, the interlace roughness and MR ratio in the annealed [NiMn] superlattice and pinned NiFe/Co layer increased more than those in the annealed [Ni/Mn] superlattice and pinned NiFe layers respectively.

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Optoelectronic Properties of Semiconductor-Atomic Superlattice Diode for SOI Applications (SOI 응용을 위한 반도체-원자 초격자 다이오드의 광전자 특성)

  • 서용진
    • Journal of the Microelectronics and Packaging Society
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    • v.10 no.3
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    • pp.83-88
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    • 2003
  • The optoelectronic characteristics of semiconducto-atomic superlattice as a function of deposition temperature and annealing conditions have been studied. The nanocrystalline silicon/adsorbed oxygen superlattice formed by molecular beam epitaxy(MBE) system. As an experimental result, the superlattice with multilayer Si-O structure showed a stable photoluminescence(PL) and good insulating behavior with high breakdown voltage. This is very useful promise for Si-based optoelectronics and quantum devices as well as for the replacement of silicon-on-insulator (SOI) in ultra-high speed and lower power CMOS devices in the future, and it can be directly integrated with silicon ULSI processing.

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Analysis of Nano-Scale Heat Conduction in the Quantum Dot Superlattice by Ballistic Diffusive Approximation (Ballistic Diffusive Approximation에 의한 Quantum Dot Superlattice의 나노열전달 해석)

  • Kim, Won-Kap;Chung, Jae-Dong
    • Proceedings of the KSME Conference
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    • pp.1376-1381
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    • 2004
  • Understanding the thermal conductivity and heat transfer processes in superlattice structures is critical for the development of thermoelectric materials and optoelectronic devices based on quantum structures. $Chen^{(1)}$ developed ballistic diffusive equation(BDE) for alternatives of the Boltzmann equation that can be applied to the complex geometrical situation. In this study, a simulation code based on BDE is developed and applied to the 1-dimensional transient heat conduction across a thin film and transient 2-dimensional heat conduction across the film with heater. The obtained results are compared to the results of the $Chen^{(1)}$ and Yang and $Chen^{(1)}$. Finally, steady 2-dimensional heat conduction in the quantum dot superlattice are solved to obtain the equivalent thermal conductivity of the lattice and also compared with the experimental data from $Borca-Tasciuc^{(2)}$.

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HgTe/Cdte superlattices grown on CdZnTe(211)B by MBE

  • Kang, T.W.;Jeong, C.S.;Leem, J.H.;Ryu, Y.S.;Hyun, J.K.;Jeon, H.C.;Lee, H.Y.;Han, M.S.
    • Journal of the Korean Vacuum Society
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    • v.6 no.S1
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    • pp.34-42
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    • 1997
  • Hg-Te-CdTe superlattices have received much interests over the last several years as a potential material for its applications for detecting devices and optoelectronics. We have grown the HgTe-CdTe superlattice using MBE. in our lab. We have carried out DCRC spectroscopy after growth of HgTe-CdTe superlattice with varying the superlattice periods and controlling the barrier thickness and we have that the presence of the main peak and the satellite peaks. We obtained 20 arcsec of FWHM over 100 periods of superlattice. We also note that high peak intensity shows the high quality of the sample and each layer of superlattice has abrupt interfaces. The angular separation between the main peak(m=0) and the first satellite peak(m=$\pm$1) is increased when the barrier layer thickness in superlatice layers are decreased. The separation between the first setellite peak(m=$\pm$1) and the second satellite peak(m$\pm$2) is increased similarly. The number of the satellite peak is a qualitative measure of the interfacial abruptness of the superlattice.

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Properties of MTiO3 (M = Sr, Ba) and PbM'O3(M'= Ti, Zr) Superlattice Thin Films Fabricated by Laser Ablation

  • Lim, T.M.;Park, J.Y.;Han, J.S.;Hwang, P.G.;Lee, K.H.;Jung, K.W.;Jung, D.
    • Bulletin of the Korean Chemical Society
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    • v.30 no.1
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    • pp.201-204
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    • 2009
  • $BaTiO_3/SrTiO_3$ and $PbTiO_3/PbZrO_3$ superlattice thin films were fabricated on $Pt/Ti/SiO_2/Si$ substrate by the pulsed laser deposition process. The morphologies and physical properties of deposited films were characterized by using X-ray diffractometer, HR-SEM, and Impedance Analyzer. XRD data and SEM images of the films indicate that each layer was well deposited alternatively in the superlattice structure. The dielectric constant of $BaTiO_3/SrTiO_3$ superlattice thin film was higher than that of individual $BaTiO_3$ or $SrTiO_3$ film. Same result was obtained in the $PbTiO_3/PbZrO_3$system. The dielectric constant of a superlattice film was getting higher as the number of layer is increased.

Growth and dielectric Properties or $BaTiO_3/SrTiO_3$ oxide artificial superlattice deposited by pulsed laser deposition (PLD) (Pulsed laser depostion (PLD)법으로 증착된 $BaTiO_3/SrTiO_3$ 산화물 초격자의 성장 및 유전특성)

  • 김주호;김이준;정동근;김용성;이재찬
    • Journal of the Korean Vacuum Society
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    • v.11 no.3
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    • pp.166-170
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    • 2002
  • Artificial $BaTiO_3$(BTO)/$SrTiO_3$(STO) oxide superlattice have been deposited on MgO (100) single crystal substrate by pulsed laser deposition(PLD) method. The stacking periodicity of BTO/STO superlattice structure was varied from $BTO_{1\;unit\; cell}/STO_{1\;unit\; cell}$ to $BTO_{125\;unit\; cell}/STO_{125 \;unit \;cell}$ thickness with the total thickness of 100 nm. The result of X-ray diffraction showed the characteristics of superlattice in the BTO/STO multilayer structure. we have also confirmed that there was no interdiffusion at the interface between BTO and STO layers by high resolution transmission electron microscopy(HRTEM). The dielectric constant of superlattice increased with decreasing stacking periodicity of the BTO/STO superlattice within the critical thickness. The dielectric constant of the BTO/STO superlattice reached a maximum i.e., 1230 at a stacking perioicity of $BTO_{2\;unit\; cell}/STO_{2\;unit\; cell}$ .

Ridge Formation by Dry-Etching of Pd and AlGaN/GaN Superlattice for the Fabrication of GaN Blue Laser Diodes

  • Kim, Jae-Gwan;Lee, Dong-Min;Park, Min-Ju;Hwang, Seong-Ju;Lee, Seong-Nam;Gwak, Jun-Seop;Lee, Ji-Myeon
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.391-392
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    • 2012
  • In these days, the desire for the precise and tiny displays in mobile application has been increased strongly. Currently, laser displays ranging from large-size laser TV to mobile projectors, are commercially available or due to appear on the market [1]. In order to achieve a mobile projectors, the semiconductor laser diodes should be used as a laser source due to their size and weight. In this presentation, the continuous etch characteristics of Pd and AlGaN/GaN superlattice for the fabrication of blue laser diodes were investigated by using inductively coupled $CHF_3$ and $Cl_2$ -based plasma. The GaN laser diode samples were grown on the sapphire (0001) substrate using a metal organic chemical vapor deposition system. A Si-doped GaN layer was grown on the substrate, followed by growth of LD structures, including the active layers of InGaN/GaN quantum well and barriers layer, as shown in other literature [2], and the palladium was used as a p-type ohmic contact metal. The etch rate of AlGaN/GaN superlattice (2.5/2.5 nm for 100 periods) and n-GaN by using $Cl_2$ (90%)/Ar (10%) and $Cl_2$ (50%)/$CHF_3$ (50%) plasma chemistry, respectively. While when the $Cl_2$/Ar plasma were used, the etch rate of AlGaN/GaN superlattice shows a similar etch rate as that of n-GaN, the $Cl_2/CHF_3$ plasma shows decreased etch rate, compared with that of $Cl_2$/Ar plasma, especially for AlGaN/GaN superlattice. Furthermore, it was also found that the Pd which is deposited on top of the superlattice couldn't be etched with $Cl_2$/Ar plasma. It was indicating that the etching step should be separated into 2 steps for the Pd etching and the superlattice etching, respectively. The etched surface of stacked Pd/superlattice as a result of 2-step etching process including Pd etching ($Cl_2/CHF_3$) and SLs ($Cl_2$/Ar) etching, respectively. EDX results shows that the etched surface is a GaN waveguide free from the Al, indicating the SLs were fully removed by etching. Furthermore, the optical and electrical properties will be also investigated in this presentation. In summary, Pd/AlGaN/GaN SLs were successfully etched exploiting noble 2-step etching processes.

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Determination of the Effective Elastic Constants of a Superlattice Film by Measuring SAW Velocities (표면탄성파 전파속도 측정에 의한 초격자 다층박막의 유효탄성계수 결정)

  • 김진오
    • The Journal of the Acoustical Society of Korea
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    • v.19 no.5
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    • pp.41-45
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    • 2000
  • The effective elastic constants of a single-crystal superlattice film have been determined by two methods based on the velocities of surface acoustic waves (SAW). One method uses formulas to calculate the effective elastic constants of a superlattice from the known elastic constants of the constituent layers. The calculated effective elastic constants are tested by comparing the corresponding SAW velocities calculated for thin-film/substrate systems with the corresponding SAW velocities measured by line-focus acoustic microscopy (LFAM). The other method determines the effective elastic constants of the superlattices by inverting the SAW velocity dispersion data measured by LFAM. The results of both methods applied to a TiN/NbN superlattice film are in good agreement.

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Optoelectronic Characteristics of Hydrogen and Oxygen Annealed Si-O Superlattice Diode

  • Seo, Yong-Jin
    • Transactions on Electrical and Electronic Materials
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    • v.2 no.2
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    • pp.16-20
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    • 2001
  • Optoelectronic characteristics of the superlattice diode as a function of deposition temperature and annealing conditions have been studied. The multilayer nanocrystalline silicon/adsorbed oxygen (nc/Si/O) superlattice formed by molecular beam epitaxy (MBE) system. Experimental results showed that deposition temperature of 550$^{\circ}C$, followed by hydrogen annealing leads to best results, in terms of optical photoluminescence (PL) and electrical current-voltage (I-V) characteristics. Consequently, the experimental results of multilayer Si/O superlattic device showed the stable photoluminescence and good insulating behavior with high breakdown voltage. This is very useful promise for Si-based optoelectronic devices, and can be readily integrated with conventional silicon ULSI processing.

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Second Harmonic Generation on the Surface of Porous Silicon Superlattice (초격자 다공질규소 표면에서 제 2고조파 발생)

  • Cho, Chang-Ho;Park, Jong-Dae
    • The Journal of Natural Sciences
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    • v.12 no.1
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    • pp.31-39
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    • 2002
  • Second harmonic generation was measured in porous silicon superlattices surface which were made by changing and anodization current density and the anodization time periodically in the process of obtaining porous silicon. The technique of second harmonic generation is used as a probe to the surface of porous silicon superlattice by using Nd:YAG laser. We have investigated the surface structure and nonlinear-optics properties of porous silicon superlattice.

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