Publications by authors named "Hyeongtag Jeon"

16 Publications

  • Page 1 of 1

The effect of an annealing process on atomic layer deposited TiO2 thin films.

Nanotechnology 2021 Oct 12. Epub 2021 Oct 12.

Division of Materials Science and Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-ku, Seoul 133-791, KOREA, Seongdong-gu, 04763, Korea (the Republic of).

In this paper, we study the property changes in TiO2 thin films related to annealing under various conditions. XPS analysis showed that the concentration of oxygen vacancies in TiO2 thin films was reduced by annealing. In the case of annealing in an O2 and air atmosphere, the oxygen vacancy concentration was reduced to the greatest extent as oxygen diffused into the TiO2 thin film and rearrangement of atoms occurred. XRD analysis showed that the anatase structure of annealed TiO2 thin films was clearly present compared to the as-deposited TiO2 thin film. I-V analysis showed that the lower the concentration of oxygen vacancy, the lower the leakage current (O2 annealed TiO2 : 10-4A/cm2) than as dep TiO2 thin film(~10-1A/cm2). The dielectric constant of annealed TiO2 thin films was 26-30 which was higher than the as-deposited TiO2 thin film (k~18) because the anatase structure became more apparent.
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http://dx.doi.org/10.1088/1361-6528/ac2f28DOI Listing
October 2021

Accelerated temperature and humidity testing of 2D SnS thin films made via four-inch-wafer-scale atomic layer deposition.

Nanotechnology 2020 Aug 13;31(35):355702. Epub 2020 May 13.

Department of Nanoscale Semiconductor Engineering, Hanyang University, Seoul, Korea.

Tin disulfide (SnS) has emerged as a promising two-dimensional (2D) material due to its excellent electrical and optical properties. However, research into 2D SnS has mainly focused on its synthesis procedures and applications; its stability to humidity and temperature has yet to be studied. In this work, 2D SnS thin films were grown by atomic layer deposition (ALD) and characterized by various tools, such as x-ray diffraction, Raman analysis, and transmission electron spectroscopy. Characterization reveals that ALD-grown SnS thin films are a high-quality 2D material. After characterization, a four-inch-wafer-scale uniformity test was performed by Raman analysis. Owing to the quality, large-area growth enabled by the ALD process, 98.72% uniformity was obtained. Finally, we calculated the thermodynamic equations for possible reactions between SnS and HO to theoretically presurmise the oxidation of SnS during accelerated humidity and temperature testing. After the accelerated humidity and temperature test, x-ray diffraction, Raman analysis, and Auger electron spectroscopy were performed to check whether SnS was oxidized or not. Our data revealed that 2D SnS thin films were stable at humid conditions.
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http://dx.doi.org/10.1088/1361-6528/ab92ccDOI Listing
August 2020

Investigation of the growth of few-layer SnS thin films via atomic layer deposition on an O plasma-treated substrate.

Nanotechnology 2020 Apr 16;31(26):265604. Epub 2020 Mar 16.

Department of Nanoscale Semiconductor Engineering, Hanyang University, Seoul, Korea.

Despite increasing interest in tin disulfide (SnS) as a two-dimensional (2D) material due to its promising electrical and optical properties, the surface treatment of silicon dioxide (SiO) substrates prior to the atomic layer deposition (ALD) deposition of SnS has not been thoroughly studied. In this paper, we prepared two types of SiO substrates with and without using an O plasma surface treatment and compared the ALD growth behavior of SnS on the SiO substrates. The hydrophilic properties of the two SiO substrates were investigated by x-ray photoelectron spectroscopy and contact angle measurements, which showed that using an O plasma surface treatment tuned the surface to be more hydrophilic. ALD-grown SnS thin films on the two different SiO substrates were characterized by x-ray diffraction, Raman spectroscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. To estimate the exact thickness of the ALD-grown SnS thin films, transmission electron microscopy was used. Our data revealed that using O plasma surface treatment increased the growth rate of the initial ALD stage. Thus, the ALD-grown SnS thin film on the SiO substrate treated with O plasma was thicker than the film grown on the non-treated SiO substrate.
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http://dx.doi.org/10.1088/1361-6528/ab8041DOI Listing
April 2020

Layered deposition of SnS grown by atomic layer deposition and its transport properties.

Nanotechnology 2019 Oct 27;30(40):405707. Epub 2019 Jun 27.

Department of Nanosclae Semiconductor Engineering, Hanyang University, Seoul, Republic of Korea.

In this work, we report on the layered deposition of few-layer tin disulfide (SnS) using atomic layer deposition (ALD). By varying the ALD cycles it was possible to deposit poly-crystalline SnS with small variation in layer numbers. Based on the ALD technique, we developed the process technology growing few-layer crystalline SnS film (3-6 layers) and we investigated their electrical properties by fabricating bottom-gated thin film transistors using the ALD SnS as the transport channel. SnS devices showed typical n-type characteristic with on/off current ratio of ∼8.32 × 10, threshold voltage of ∼2 V, and a subthreshold swing value of 830 mV decade for the 6 layers SnS. The developed SnS ALD technique may aid the realization of two-dimensional SnS based flexible and wearable devices.
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http://dx.doi.org/10.1088/1361-6528/ab2d89DOI Listing
October 2019

Terahertz rectification in ring-shaped quantum barriers.

Nat Commun 2018 11 21;9(1):4914. Epub 2018 Nov 21.

Department of Physics and Astronomy and Center for Atom Scale Electromagnetism, Seoul National University, Seoul, 08826, Korea.

Tunneling is the most fundamental quantum mechanical phenomenon with wide-ranging applications. Matter waves such as electrons in solids can tunnel through a one-dimensional potential barrier, e.g. an insulating layer sandwiched between conductors. A general approach to control tunneling currents is to apply voltage across the barrier. Here, we form closed loops of tunneling barriers exposed to external optical control to manipulate ultrafast tunneling electrons. Eddy currents induced by incoming electromagnetic pulses project upon the ring, spatiotemporally changing the local potential. The total tunneling current which is determined by the sum of contributions from all the parts along the perimeter is critically dependent upon the symmetry of the loop and the polarization of the incident fields, enabling full-wave rectification of terahertz pulses. By introducing global geometry and local operation to current-driven circuitry, our work provides a novel platform for ultrafast optoelectronics, macroscopic quantum phenomena, energy harvesting, and multi-functional quantum devices.
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http://dx.doi.org/10.1038/s41467-018-07365-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6249216PMC
November 2018

Characterization of Ti-doped TiO based composite electrode for lithium polymer secondary batteries.

Nanotechnology 2018 Nov 23;29(44):445402. Epub 2018 Aug 23.

Advanced Materials Division, Korea Research Institute of Chemical Technology, 141 Gajeongro, Yuseong, Daejeon 34114, Republic of Korea. Department of Material Science and Engineering, Hanyang University, Seongdong-gu, Seoul 04763, Republic of Korea.

Ti-doped TiO nanoparticles were synthesized and fabricated into a composite electrode as an anode material for lithium polymer batteries. The composite electrode contained polymer electrolyte (PE) to reduce interfacial resistance between the solid PE and electrode. The effect of PE content on the composite electrodes was analyzed by GITT, and it was found that PE significantly influenced lithium storage as well as internal resistance. A composite electrode was fabricated into a pouch type cell and exhibited a capacity of 160 mAh g in the bent state, demonstrating the applicability of the Ti-doped TiO based composite electrode in lithium polymer secondary batteries.
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http://dx.doi.org/10.1088/1361-6528/aadc6fDOI Listing
November 2018

Fabrication of high crystalline SnS and SnS thin films, and their switching device characteristics.

Nanotechnology 2018 May 2;29(21):215201. Epub 2018 Mar 2.

Division of Materials Science and Engineering, Hanyang University, Seoul, Republic of Korea.

Representative tin sulfide compounds, tin monosulfide (SnS) and tin disulfide (SnS) are strong candidates for future nanoelectronic devices, based on non-toxicity, low cost, unique structures and optoelectronic properties. However, it is insufficient for synthesizing of tin sulfide thin films using vapor phase deposition method which is capable of fabricating reproducible device and securing high quality films, and their device characteristics. In this study, we obtained highly crystalline SnS thin films by atomic layer deposition and obtained highly crystalline SnS thin films by phase transition of the SnS thin films. The SnS thin film was transformed into SnS thin film by annealing at 450 °C for 1 h in HS atmosphere. This phase transition was confirmed by x-ray diffractometer and x-ray photoelectron spectroscopy, and we studied the cause of the phase transition. We then compared the film characteristics of these two tin sulfide thin films and their switching device characteristics. SnS and SnS thin films had optical bandgaps of 1.35 and 2.70 eV, and absorption coefficients of about 10 and 10 cm in the visible region, respectively. In addition, SnS and SnS thin films exhibited p-type and n-type semiconductor characteristics. In the images of high resolution-transmission electron microscopy, SnS and SnS directly showed a highly crystalline orthorhombic and hexagonal layered structure. The field effect transistors of SnS and SnS thin films exhibited on-off drain current ratios of 8.8 and 2.1 × 10 and mobilities of 0.21 and 0.014 cm V s, respectively. This difference in switching device characteristics mainly depends on the carrier concentration because it contributes to off-state conductance and mobility. The major carrier concentrations of the SnS and SnS thin films were 6.0 × 10 and 8.7 × 10 cm, respectively, in this experiment.
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http://dx.doi.org/10.1088/1361-6528/aab3c1DOI Listing
May 2018

Tunnelling current-voltage characteristics of Angstrom gaps measured with terahertz time-domain spectroscopy.

Sci Rep 2016 06 30;6:29103. Epub 2016 Jun 30.

Department of Physics and Astronomy and Center for Atom Scale Electromagnetism, Seoul National University, Seoul 08826, Korea.

Quantum tunnelling becomes inevitable as gap dimensions in metal structures approach the atomic length scale, and light passing through these gaps can be used to examine the quantum processes at optical frequencies. Here, we report on the measurement of the tunnelling current through a 3-Å-wide metal-graphene-metal gap using terahertz time-domain spectroscopy. By analysing the waveforms of the incident and transmitted terahertz pulses, we obtain the tunnelling resistivity and the time evolution of the induced current and electric fields in the gap and show that the ratio of the applied voltage to the tunnelling current is constant, i.e., the gap shows ohmic behaviour for the strength of the incident electric field up to 30 kV/cm. We further show that our method can be extended and applied to different types of nanogap tunnel junctions using suitable equivalent RLC circuits for the corresponding structures by taking an array of ring-shaped nanoslots as an example.
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http://dx.doi.org/10.1038/srep29103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4928118PMC
June 2016

Improvement in the Positive Bias Temperature Stability of SnOx-Based Thin Film Transistors by Hf and Zn Doping.

J Nanosci Nanotechnol 2015 Oct;15(10):7606-10

We investigated the performance of tin oxide thin film transistors (TFTs) using DC magnetron sputtering. A remarkable improvement in the transfer characteristics was obtained for the Hf-doped tin oxide (HTO) TFT. We also developed amorphous hafnium-zinc-tin oxide (HZTO) thin film transistors and investigated the effects of hafnium doping on the electrical characteristics of the HTO TFTs. Doping with hafnium resulted in a reduced defect density in the tin oxide channel layer related to oxygen vacancies, which may result from increased field effect mobility. Zinc atoms have relatively higher oxidation potential compared to tin atoms, so more oxygen molecules can be absorbed and more electrons are trapped in the HZTO films. The HZTO TFTs exhibited good electrical characteristics with a field effect mobility of 10.98 cm2/Vs, and a high ION/IOFF ratio over 10(8).
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http://dx.doi.org/10.1166/jnn.2015.11155DOI Listing
October 2015

Terahertz Quantum Plasmonics of Nanoslot Antennas in Nonlinear Regime.

Nano Lett 2015 Oct 22;15(10):6683-8. Epub 2015 Sep 22.

Department of Physics and Astronomy and Center for Atom Scale Electromagnetism, Seoul National University , Seoul 08826, Korea.

Quantum tunneling in plasmonic nanostructures has presented an interesting aspect of incorporating quantum mechanics into classical optics. However, the study has been limited to the subnanometer gap regime. Here, we newly extend quantum plasmonics to gap widths well over 1 nm by taking advantage of the low-frequency terahertz regime. Enhanced electric fields of up to 5 V/nm induce tunneling of electrons in different arrays of ring-shaped nanoslot antennas of gap widths from 1.5 to 10 nm, which lead to a significant nonlinear transmission decrease. These observations are consistent with theoretical calculations considering terahertz-funneling-induced electron tunneling across the gap.
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http://dx.doi.org/10.1021/acs.nanolett.5b02505DOI Listing
October 2015

Investigation of the flatband voltage (V(FB)) shift of Al2O3 on N2 plasma treated Si substrate.

J Nanosci Nanotechnol 2013 Sep;13(9):6275-9

Department of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea.

The relationships between the physical and electrical characteristics of films treated with N2 plasma followed by forming gas annealing (FGA) were investigated. The Si substrates were treated with various radio frequency (RF) power levels under a N2 ambient. Al2O3 films were then deposited on Si substrates via remote plasma atomic-layer deposition. The plasma characteristics, such as the radical and ion density, were investigated using optical emission spectroscopy. Through X-ray photoelectron spectroscopy, the chemical-bonding configurations of the samples treated with N2 plasma and FGA were examined. The quantity of Si-N bonds increased as the RF power was increased, and Si--O--N bonds were generated after FGA. The flatband voltage (VFB) was shifted in the negative direction with increasing RF power, but the VFB values of the samples after FGA shifted in the positive direction due to the formation of Si--O--N bonds. N2 plasma treatment with various RF power levels slightly increased the leakage current due to the generation of defect sites.
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http://dx.doi.org/10.1166/jnn.2013.7707DOI Listing
September 2013

Tuning the electronic structure of tin sulfides grown by atomic layer deposition.

ACS Appl Mater Interfaces 2013 Sep 16;5(18):8889-96. Epub 2013 Sep 16.

Department of Materials Science and Engineering, Hanyang University , Seoul, 133-791 Korea.

In this study, tin sulfide thin films were obtained by atomic layer deposition (ALD) using Tetrakis(dimethylamino)tin (TDMASn, [(CH3)2N]4Sn) and hydrogen sulfide (H2S). The growth rate of the tin sulfides (SnSx) was shown to be highly dependent on the deposition temperature, and reaction times of 1 second for the TDMASn and H2S were required to reach the saturation regime. Surface morphologies were smooth or rectangular with rounded corners as observed by a field emission scanning electron microscope (FE-SEM) and were dependent on temperature. X-ray diffraction results confirmed that the crystal structure of SnSx can be tuned by changing the ALD temperature. Below 120 °C, SnSx films appeared to be amorphous. In addition, SnSx films were SnS2 hexagonal at 140 and 150 °C and SnS orthorhombic above 160 °C. Similarly, the values of the optical band gap and binding energy showed significant differences between 150 and 160 °C. The electronic structures of SnSx were extracted by UPS and absorption spectroscopy, and the unsaturated Sn 3d molecular orbital (MO) states in the band edge were found to be responsible for the great improvement in electrical conductivity. This study shows that TDMASn-H2S ALD is an effective deposition method for SnSx films, offering a simple approach to tune the physical properties.
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http://dx.doi.org/10.1021/am401127sDOI Listing
September 2013

Photocurrent detection of chemically tuned hierarchical ZnO nanostructures grown on seed layers formed by atomic layer deposition.

Nanoscale Res Lett 2012 Jun 6;7(1):290. Epub 2012 Jun 6.

Division of Materials Science and Engineering, Hanyang University, Seongdong-gu, Seoul, 133-791, South Korea.

We demonstrate the morphological control method of ZnO nanostructures by atomic layer deposition (ALD) on an Al2O3/ZnO seed layer surface and the application of a hierarchical ZnO nanostructure for a photodetector. Two layers of ZnO and Al2O3 prepared using ALD with different pH values in solution coexisted on the alloy film surface, leading to deactivation of the surface hydroxyl groups. This surface complex decreased the ZnO nucleation on the seed layer surface, and thereby effectively screened the inherent surface polarity of ZnO. As a result, a 2-D zinc hydroxyl compound nanosheet was produced. With increasing ALD cycles of ZnO in the seed layer, the nanostructure morphology changes from 2-D nanosheet to 1-D nanorod due to the recovery of the natural crystallinity and polarity of ZnO. The thin ALD ZnO seed layer conformally covers the complex nanosheet structure to produce a nanorod, then a 3-D, hierarchical ZnO nanostructure was synthesized using a combined hydrothermal and ALD method. During the deposition of the ALD ZnO seed layer, the zinc hydroxyl compound nanosheets underwent a self-annealing process at 150 °C, resulting in structural transformation to pure ZnO 3-D nanosheets without collapse of the intrinsic morphology. The investigation on band electronic properties of ZnO 2-D nanosheet and 3-D hierarchical structure revealed noticeable variations depending on the richness of Zn-OH in each morphology. The improved visible and ultraviolet photocurrent characteristics of a photodetector with the active region using 3-D hierarchical structure against those of 2-D nanosheet structure were achieved.
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http://dx.doi.org/10.1186/1556-276X-7-290DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3432614PMC
June 2012

Properties of flexible phosphorescence polymer light emitting diodes coated on polyethylenenaphthalate plastic substrates.

J Nanosci Nanotechnol 2012 Feb;12(2):1585-8

Department of Electronics Engineering, Dankook University, Cheonan 330-714, Korea.

Flexible phosphorescence polymer light emitting diodes (PhPLEDs) with PEN/ITO/PEDOT:PSS/ PVK:Ir(ppy)3/TPBI/LiF/Al structure were fabricated to investigate the effects of Ir(ppy)3 doping concentrations on the optical and electrical properties of the devices. PVK and Ir(ppy)3 conjugated polymers as host and guest materials in the emission layer were spun coated at various concentrations of Ir(ppy)3 ranging from 2.0 to 8.0 vol%. As the concentration of Ir(ppy)3 increased from 2.0 to 6.0 vol%, the electrical and optical properties of the flexible PhPLEDs were improved clearly. Maximum luminance and current density were obtained for a PhPLED with an Ir(ppy)3 concentration of 6.0 vol%, with 6815 cd/m2 and 393 mA/cm2 at 9 V. The current efficiency tends to increase with the Ir(ppy)3 concentration, because of the formation of the excitons required to emit light.
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http://dx.doi.org/10.1166/jnn.2012.4582DOI Listing
February 2012

The effect of annealing ambient on the characteristics of an indium-gallium-zinc oxide thin film transistor.

J Nanosci Nanotechnol 2011 Jul;11(7):6029-33

Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea.

In this study, the effects of different annealing conditions (air, O2, N2, vacuum) on the chemical and electrical characteristics of amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFT) were investigated. The contact resistance and interface properties between the IGZO film and the gate dielectric improved after an annealing treatment. However, the chemical bonds in the IGZO bulk changed under various annealing atmospheres, which, in turn, altered the characteristics of the TFTs. The TFTs annealed in vacuum and N2 ambients exhibited undesired switching properties due to the high carrier concentration (>10(17) cm(-3)) of the IGZO active layer. In contrast, the IGZO TFTs annealed in air and oxygen ambients displayed clear transfer characteristics due to an adequately adjusted carrier concentration in the operating range of the TFT. Such an optimal carrier concentration arose through the stabilization of unstable chemical bonds in the IGZO film. With regard to device performance, the TFTs annealed in O2 and air exhibited saturation mobility values of 8.29 and 7.54 cm2/Vs, on-off ratios of 7.34 x 10(8) and 3.95 x 10(8), and subthreshold swing (SS) values of 0.23 and 0.19 V/decade, respectively. Therefore, proper annealing ambients contributed to internal modifications in the IGZO structure and led to an enhancement in the oxidation state of the metal. As a result, defects such as oxygen vacancies were eliminated. Oxygen annealing is thus effective for controlling the carrier concentration of the active layer, decreasing electron traps, and enhancing TFT performance.
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http://dx.doi.org/10.1166/jnn.2011.4360DOI Listing
July 2011

Change in the interfacial reaction of Hf-silicate film as a function of thickness and stoichiometry.

J Chem Phys 2008 Jul;129(3):034705

Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, South Korea.

Medium energy ion scattering and high-resolution transmission electron microscopy are used to investigate the depth of the interfacial reaction of Hf-silicate film. The interfacial reaction is critically affected by the film thickness and the mole fraction of HfO(2) in silicate film. The interfacial compressive strain generated at the surface of the Si substrate is dependent on the film thickness during the postannealing process in film with a thickness of approximately 4 nm. Finally, the phase separation phenomenon demonstrates critically different behaviors at different film thicknesses and stoichiometries because the diffusion of Si from interface to surface is dependent on these factors. Moreover, the oxidation by oxygen impurity in the inert ambient causes SiO(2) top formation.
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http://dx.doi.org/10.1063/1.2955461DOI Listing
July 2008
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