• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.748-753
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• 2009

The surface morphology and the surface roughness of n-type SiC induced by wet-treatment using 45% KOH and buffered oxide etchant (BOE-1HF : $6H_2O$) were investigated by atomic force microscopy (AFM). While Si-face of SiC could be etched by alkali solutions such as KOH, acidic solutions such as BOE were hardly able to etch SiC. When the rough SiC samples were used, the surface roughness of etched sample was decreased after wet-treatment regardless of etchant, due to the planarization the of surface by widening of scratches formed by mechanical polishing. It was observed that the initial etching was affected by the energetically unstable sites, such as dangling bond and steps. However, when a relatively smooth sample was used, the surface roughness was rapidly increased after treatment at $180^{\circ}C$ for 1 hr and at room temperature for 4 hr by using KOH solution, resulting from the nano-sized structures such as pores and bumps. This indicates that porous SiC surface can be achieved by using purely chemical treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.3
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• pp.264-268
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• 2022

High pressure deuterium (HPD) annealing is an advancing technology for the fabrication of modern semiconductor devices. In this work, gate-enclosed FETs are fabricated on a silicon substrate as test vehicles. After a cycle for the HPD annealing, the device parameters such as threshold voltage (V_TH), subthreshold swing (SS), on-state current (I_ON), off-state current (I_OFF), and gate leakage (I_G) were measured and compared depending on the HPD. The HPD annealing can passivate the dangling bonds at Si-SiO₂ interfaces as well as eliminate the bulk trap in SiO₂. It can be concluded that adding the HPD annealing as a fabrication process is very effective in improving device reliability, performance, and variability.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.581-586
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• 2010

The porous Si (PS) was annealed at various temperature in air, argon, and nitrogen atmosphere. Structural and optical properties of the annealed PS were investigated by scanning electron microscopy (SEM) and photoluminescence (PL). It is found that the shape of pore is changed from circle to channel as increasing annealing temperature which was annealed in air and argon atmosphere. In case of PS annealed in nitrogen atmosphere, the shape of pore is changed from channel to circle with increase annealing temperature from 600 to $800^{\circ}C$. The PL peak position is blue-shifted with increasing annealing temperature. As annealing temperature increases, the PL intensity of the PS annealed in argon is decreased but that of the PS annealed in nitrogen is increased. It might be due to the formation of Si-N bonds and it passivates the non-radiative centers which is Si dangling bonds on the surface of the PS.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.2
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• pp.179-184
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• 2016

In recent years, the on-resistance, power loss and cell density of Si power devices have not exhibited significant improvements, and performance is approaching the material limits. GaN is considered an attractive material for future high-power applications because of the wide band-gap, large breakdown field, high electron mobility, high switching speed and low on-resistance. Here we report on the Ohmic contact resistance and reverse-bias characteristics of AlGaN/GaN Schottky barrier diodes with and without annealing. Annealing in oxygen at $500^{\circ}C$ resulted in an increase in the breakdown voltage from 641 to 1,172 V for devices with an anode-cathode separation of $20{\mu}m$. However, these annealing conditions also resulted in an increase in the contact resistance of $0.183{\Omega}-mm$, which is attributed to oxidation of the metal contacts. Auger electron spectroscopy revealed diffusion of oxygen and Au into the AlGaN and GaN layers following annealing. The improved reverse-bias characteristics following annealing in oxygen are attributed to passivation of dangling bonds and plasma damage due to interactions between oxygen and GaN/AlGaN. Thermal annealing is therefore useful during the fabrication of high-voltage GaN devices, but the effects on the Ohmic contact resistance should be considered.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.308-309
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• 2016

Reducing surface recombination is a critical factor for high efficiency silicon solar cells. The passivation process is for reducing dangling bonds which are carrier. Tunnel oxide layer is one of main issues to achieve a good passivation between silicon wafer and emitter layer. Many research use wet-chemical oxidation or thermally grown which the highest conversion efficiencies have been reported so far. In this study, we deposit ultra-thin tunnel oxide layer by PECVD (Plasma Enhanced Chemical Vapor Deposition) using $N_2O$ plasma. Both side deposit tunnel oxide layer in different RF-power and phosphorus doped a-Si:H layer. After deposit, samples are annealed at $850^{\circ}C$ for 1 hour in $N_2$ gas atmosphere. After annealing, samples are measured lifetime and implied Voc (iVoc) by QSSPC (Quasi-Steady-State Photo Conductance). After measure, samples are annealed at $400^{\circ}C$ for 30 minute in $Ar/H_2$ gas atmosphere and then measure again lifetime and implied VOC. The lifetime is increase after all process also implied VOC. The highest results are lifetime $762{\mu}s$, implied Voc 733 mV at RF-power 200 W. The results of C-V measurement shows that Dit is increase when RF-power increase. Using this optimized tunnel oxide layer is attributed to increase iVoc. As a consequence, the cell efficiency is increased such as tunnel mechanism based solar cell application.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.281.1-281.1
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• 2016

Transition metal dichalcogenides (TMDCs) are promising layered structure materials for next-generation nano electronic devices. Many investigation on the FET device using TMDCs channel material have been performed with some integrated approach. To use TMDCs for channel material of top-gate thin film transistor(TFT), the study on high-k dielectrics on TMDCs is necessary. However, uniform growth of atomic-layer-deposited high-k dielectric film on TMDCs is difficult, owing to the lack of dangling bonds and functional groups on TMDC's basal plane. We demonstrate the effect of remote oxygen plasma pretreatment of large area synthesized few-layer MoSe2 on the growth behavior of Al2O3, which were formed by atomic layer deposition (ALD) using tri-methylaluminum (TMA) metal precursors with water oxidant. We investigated uniformity of Al2O3 by Atomic force microscopy (AFM) and Scanning electron microscopy (SEM). Raman features of MoSe2 with remote plasma pretreatment time were obtained to confirm physical plasma damage. In addition, X-ray photoelectron spectroscopy (XPS) was measured to investigate the reaction between MoSe2 and oxygen atom after the remote O2 plasma pretreatment. Finally, we have uniform Al2O3 thin film on the MoSe2 by remote O2 plasma pretreatment before ALD. This study can provide interfacial engineering process to decrease the leakage current and to improve mobility of top-gate TFT much higher.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.294.1-294.1
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• 2016

Transition metal dichalcogenides (TMDs) with two-dimensional layered structure, such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2), are considered attractive materials for future semiconductor devices due to its relatively superior electrical, optical, and mechanical properties. Their excellent scalability down to a monolayer based on the van der Waals layered structure without surface dangling bonds makes semiconductor devices based on TMD free from short channel effect. In comparison to the widely studied transistor based on MoS2, researchs focusing on WSe2 transistor are still limited. WSe2 is more resistant to oxidation in humid ambient condition and relatively air-stable than sulphides such as MoS2. These properties of WSe2 provide potential to fabricate high-performance filed-effect transistor if outstanding electronic characteristics can be achieved by suitable metal contacts and doping phenomenon. Here, we demonstrate the effect of two different metal contacts (titanium and platinum) in field-effect transistor based on WSe2, which regulate electronic characteristics of device by controlling the effective barreier height of the metal-semiconductor junction. Electronic properties of WSe2 transistor were systematically investigated through monitoring of threshold voltage shift, carrier concentration difference, on-current ratio, and field-effect mobility ratio with two different metal contacts. Additionally, performance of transistor based on WSe2 is further enhanced through reliable and controllable n-type doping method of WSe2 by triphenylphosphine (PPh3), which activates the doping phenomenon by thermal annealing process and adjust the doping level by controlling the doping concentration of PPh3. The doping level is controlled in the non-degenerate regime, where performance parameters of PPh3 doped WSe2 transistor can be optimized.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.194.1-194.1
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• 2015

Transition metal dichalcogenide (TMD) with layered structure, has recently been considered as promising candidate for next-generation flexible electronic and optoelectronic devices because of its superior electrical, optical, and mechanical properties.[1] Scalability of thickness down to a monolayer and van der Waals expitaxial structure without surface dangling bonds (consequently, native oxides) make TMD-based thin film transistors (TFTs) that are immune to the short channel effect (SCE) and provide very high field effect mobility (${\sim}200cm^2/V-sec$ that is comparable to the universal mobility of Si), respectively.[2] In addition, an excellent photo-detector with a wide spectral range from ultraviolet (UV) to close infrared (IR) is achievable with using $WSe_2$, since its energy bandgap varies between 1.2 eV (bulk) and 1.8 eV (monolayer), depending on layer thickness.[3] However, one of the critical issues that hinders the successful integration of $WSe_2$ electronic and optoelectronic devices is the lack of a reliable and controllable doping method. Such a component is essential for inducing a shift in the Fermi level, which subsequently enables wide modulations of its electrical and optical properties. In this work, we demonstrate n-doping method for $WSe_2$ on poly-4-vinylphenol and poly (melamine-co-formaldehyde) (PVP/PMF) insulating layer and adjust the doping level of $WSe_2$ by controlling concentration of PMF in the PVP/PMF layer. We investigated the doping of $WSe_2$ by PVP/PMF layer in terms of electronic and optoelectronic devices using Raman spectroscopy, electrical measurements, and optical measurements.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.181-181
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• 2016

Hydrogenated microcrystalline silicon (${\mu}c-Si:H$) films have attracted much attention as materials of the bottom-cells in Si thin film tandem photovoltaics due to their low bandgap and excellent stability against light soaking. However, in PECVD, the source gas $SiH_4$ must be highly diluted by $H_2$, which eventually results in low deposition rate. Moreover, it is known that high-rate ${\mu}c-Si:H$ growth is usually accompanied by a large number of dangling-bond (DB) defects in the resulting films, which act as recombination centers for photoexcited carriers, leading to a deterioration in the device performance. During film deposition, Si nanoparticles generated in $SiH_4$ discharges can be incorporated into films, and such incorporation may have effects on film properties depending on the size, structure, and volume fraction of nanoparticles incorporated into films. Here we report experimental results on the effects of nonoparticles incorporation at the different substrate temperature studied using a multi-hollow discharge plasma CVD method in which such incorporation can be significantly suppressed in upstream region by setting the gas flow velocity high enough to drive nanoparticles toward the downstream region. All experiments were performed with the multi-hollow discharge plasma CVD reactor at RT, 100, and $250^{\circ}C$, respectively. The gas flow rate ratio of $SiH_4$ to $H_2$ was 0.997. The total gas pressure P was kept at 2 Torr. The discharge frequency and power were 60 MHz, 180 W, respectively. Crystallinity Xc of resulting films was evaluated using Raman spectra. The defect densities of the films were measured with electron spin resonance (ESR). The defect density of fims deposited in the downstream region (with nonoparticles) is higher defect density than that in the upstream region (without nanoparticles) at low substrate temperature of RT and $100^{\circ}C$. This result indicates that nanoparticle incorporation can change considerably their film properties depending on the substrate temperature.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.3
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• pp.299-304
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• 2014

The need of reusing sewage sludge is highly increasing as the amount of domestic sewage sludge is growing and sewage management strategies were reinforced. Accordingly, in this research, we studied the composting possibility of sludge in sewage treatment plant J, using dryer facility with indirect system by conducting component analysis of dried sludge and experiment on cultivating crops. It was observed from the component analysis, that the dried sludge is appropriate for both decomposed manure standard of Ministry of Environment and fertilizer standard of Rural Development Administration. Besides, in the experiment on cultivating lettuce, the experimental group(soil + dried sludge) was superior to the control group(soil + bed soil) in apparent condition of leaves tensity and damage by disease and pest. In case of cultivating tomato, the experimental group showed stronger durability of fruits dangling on stems compared to the control group after 9 weeks. Consequently, the excess sludge dried by indirect heating system in the sewage treatment plant J is appropriate for the standard of both Ministry of Environment and Rural Development Administration and show good result in experiment on cultivating crops therefore it can be reused for composting.