• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.213-220
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• 2009

The optimal condition of low temperature deposition of transparent conductive Al-doped zinc oxide (AZO) films is studied by RF magnetron sputtering method. To achieve enhanced-electrical property and good crystallites quality, we tried to deposit on glass using a two-step growth process. This process was to deposit AZO buffer layer with optimal growth condition on glass in-situ state. The AZO film grown at rf 120 W on buffer layer prepared at RF $50{\sim}60\;W$ shows the electrical resistivity $3.9{\times}10^{-4}{\Omega}cm$, Carrier concentration $1.22{\times}10^{21}/cm^3$, and mobility $9.9\;cm^2/Vs$ in these results, The crystallinity of AZO film on buffer layer was similar to that of AZO film on glass with no buffer later but the electrical properties of the AZO film were 30% improved than that of the AZO film with no buffer layer. Therefore, the cause of enhanced electrical properties was explained to be dependent on degree of crystallization and on buffer layer's compressive stress by variation of $Ar^+$ ion impinging energy.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.754-757
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• 2012

In this report, we fabricate the porous graphene films through embossing process and vacuum filtration method and demonstrate their superior electrochemical properties as supercapacitor electrode materials. Insertion/removal of polystyrene nanoparticles between the graphene sheets allows to provide pore structures, leading to the effective prevention of restacking in graphene films. As-prepared porous graphene films have a large surface area, a bicontinuous porous structures, high electrical conductivity, and excellent mechanical integrity. The electrochemical properties of the porous graphene films as electrode materials of supercapacitor are investigated by using aqueous $H_2SO_4$ and ionic liquid solution under three-electrode system. The porous graphene films exhibit a high specific capacitance (284.5 F/g), which is two-fold higher than that of packing graphene films (138.9 F/g). In addition, the rate capability (98.7% retention) and long-term cycling stability (97.2%) for the porous graphene films are significantly enhanced, due to the facilitated ion mobility between the graphene layers.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.358-358
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• 2012

The application of BZO (Boron-doped Zinc Oxide) films use as the TCO(Transparent Conductive Oxide) material for display and solar cell industries, where the conductivity of the BZO films plays a critical role for improvement of cell performance. Thin BZO films are deposited on glass substrates by using RF sputter system. Then charging flow rates of O2 gas from zero to 10 sccm, thereby controlling the impurity concentration of BZO. BZO deposited on soda lime glass and RF power was 300 W, frequency was 13.56 MHz, and working pressure was $5.0{\times}10-6$ Torr. The Substrate and glass between distance 200 mm. We measured resistivity, conductivity, mobility by hall measurement system. Optical properties measured by photo voltaic device analysis system. We measured surface build according to oxygen flow rate from XPS (X-ray Photoelectron Spectroscopy) system. The profile of the energy distribution of the electrons emitted from BZO films by the Auger neutralization is measured and rescaled so that Auger self-convolution arises, revealing the detail structure of the valence band. It may be observed coefficient ${\gamma}$ of the secondary electron emission from BZO by using ${\gamma}$-FIB (Gamma-Focused Ion Beam) system. We observed the change in electrical conductivity by correlation of the valence band structure. Therefore one of the key issues in BZO films may be the valence band that detail structure dominates performance of solar cell devices. Demonstrating the secondary electron emission by the Auger neutralization of ions is useful for the determination of the characteristics of BZO films for solar cell and display developments.

• Journal of the Korean Vacuum Society
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• v.2 no.2
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• pp.188-198
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• 1993

We have developed a technique for growing thin oxides (6~10 nm) by the Last step TCA method. N-channel metal-oxide-semiconductor (n-MOS) capacitor and n-channel metal-oxide-semiconductor field-effect transistor's (MOSFET's) having a gate oxide with chlorine incorporated $SiO_2/Si$ interface have been analyzed by electrical measurements and physical methods, such as secondary ion mass spectrometry (SIMS) and electron spectroscopy for chemical analysis (ESCA). The gate oxide grown with the Last strp TCA method has good characteristics as follows: the electron mobility of the MOSFET's with the Last step TCA method was increased by about 7% and the defect density at the $SiO_2/Si$ interface decreases slightly compared with that with No TCA method. In reliability estimation, the breakdown field was 18 MV/cm, 0.6 MV/cm higher than that of the gate oxide with No TCA method, and the lifetime estimated by TDDB measurement was longer than 20 years. The device lifetime estimated from hot-carrier reliability was proven to be enhanced. As the results, the gate oxide having a $SiO_2/Si$ interface incorporated with chlorine has good characteristics. Our new technique of Last step TCA method may be used to improve the endurance and retention of MOSFET's and to alleviate the degradation of thin oxides in short-channel MOS devices.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.614-623
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• 1993

Electrical characteristics of LiF-$Li_{2}O-B_{2}O_{3}-P_{2}O_5$ glasses with fixed $Li_2O$ content have been investigated by using AC impedance spectroscopy. Part of the total lithium ions present in these glasses contributes to conduction, and the changes in electrical conductivity with composition was inconsistent with the weak electrolyte model. The power law could not be used to determine the hopping ion concentration in these glasses. Both mobile carrier density and mobility have been modified as Li were added in the form of LiF. The formation of $(B-O-P)^-,di^-$, and metaborate group gave additional available sites for Li+ diffusion causing the enhancement of conductivity. The observed maximum conductivity was $2.43 \times 10^{-4}$S/cm at $150^{\circ}C$ at the composition containing 8mol% LiF. The decomposion potential amounted to 5.94V. The Li/glass electrolyte/$TiS_2$ solid-state cell showed open circuit voltage of 3.14V and energy density of 22 Wh/Kg at $150^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.292-292
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• 2016

Transition metal dichalcogenides (TMDs) with a two-dimensional layered structure have been considered highly promising materials for next-generation flexible, wearable, stretchable and transparent devices due to their unique physical, electrical and optical properties. Recent studies on TMD devices have focused on developing a suitable doping technique because precise control of the threshold voltage ($V_{TH}$) and the number of tightly-bound trions are required to achieve high performance electronic and optoelectronic devices, respectively. In particular, it is critical to develop an ultra-low level doping technique for the proper design and optimization of TMD-based devices because high level doping (about $10^{12}cm^{-2}$) causes TMD to act as a near-metallic layer. However, it is difficult to apply an ion implantation technique to TMD materials due to crystal damage that occurs during the implantation process. Although safe doping techniques have recently been developed, most of the previous TMD doping techniques presented very high doping levels of ${\sim}10^{12}cm^{-2}$. Recently, low-level n- and p-doping of TMD materials was achieved using cesium carbonate ($Cs_2CO_3$), octadecyltrichlorosilane (OTS), and M-DNA, but further studies are needed to reduce the doping level down to an intrinsic level. Here, we propose a novel DNA-based doping method on $MoS_2$ and $WSe_2$ films, which enables ultra-low n- and p-doping control and allows for proper adjustments in device performance. This is achieved by selecting and/or combining different types of divalent metal and trivalent lanthanide (Ln) ions on DNA nanostructures. The available n-doping range (${\Delta}n$) on the $MoS_2$ by Ln-DNA (DNA functionalized by trivalent Ln ions) is between $6{\times}10^9cm^{-2}$ and $2.6{\times}10^{10}cm^{-2}$, which is even lower than that provided by pristine DNA (${\sim}6.4{\times}10^{10}cm^{-2}$). The p-doping change (${\Delta}p$) on $WSe_2$ by Ln-DNA is adjusted between $-1.0{\times}10^{10}cm^{-2}$ and $-2.4{\times}10^{10}cm^{-2}$. In the case of Co-DNA (DNA functionalized by both divalent metal and trivalent Ln ions) doping where $Eu^{3+}$ or $Gd^{3+}$ ions were incorporated, a light p-doping phenomenon is observed on $MoS_2$ and $WSe_2$ (respectively, negative ${\Delta}n$ below $-9{\times}10^9cm^{-2}$ and positive ${\Delta}p$ above $1.4{\times}10^{10}cm^{-2}$) because the added $Cu^{2+}$ ions probably reduce the strength of negative charges in Ln-DNA. However, a light n-doping phenomenon (positive ${\Delta}n$ above $10^{10}cm^{-2}$ and negative ${\Delta}p$ below $-1.1{\times}10^{10}cm^{-2}$) occurs in the TMD devices doped by Co-DNA with $Tb^{3+}$ or $Er^{3+}$ ions. A significant (factor of ~5) increase in field-effect mobility is also observed on the $MoS_2$ and $WSe_2$ devices, which are, respectively, doped by $Tb^{3+}$-based Co-DNA (n-doping) and $Gd^{3+}$-based Co-DNA (p-doping), due to the reduction of effective electron and hole barrier heights after the doping. In terms of optoelectronic device performance (photoresponsivity and detectivity), the $Tb^{3+}$ or $Er^{3+}$-Co-DNA (n-doping) and the $Eu^{3+}$ or $Gd^{3+}$-Co-DNA (p-doping) improve the $MoS_2$ and $WSe_2$ photodetectors, respectively.