• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.1-6
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• 2014

This review article summarizes photoelectrochemical water splitting using gallium nitride (GaN). GaN materials have been studied as novel photoelectrode material due to its chemical stability and easy band gap engineering. Unlike other semiconductor materials that are easily corroded in strongly acidic or alkaline electrolyte, n-type GaN is chemically stable enough to be used as photoanode in oxygen evolution reaction. Furthermore, studies on p-type GaN have been recently reported. This review briefly discusses problems that need to be solved before GaN materials find widespread use in solar fuel application.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.256-256
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• 2012

Oxide semiconductors such as zinc tin oxide (ZTO) or indium gallium zinc oxide (IGZO) have attracted a lot of research interest owing to their high potential for application as thin film transistors (TFTs) [1,2]. However, the instability of oxide TFTs remains as an obstacle to overcome for practical applications to electronic devices. Several studies have reported that the electrical characteristics of ZnO-based transistors are very sensitive to oxygen, hydrogen, and water [3,4,5]. To improve the reliability issue for the amorphous InGaZnO (a-IGZO) thin-film transistor, back channel passivation layer is essential for the long term bias stability. In this study, we investigated the instability of amorphous indium-gallium-zinc-oxide (IGZO) thin film transistors (TFTs) by the back channel contaminations. The effect of back channel contaminations (humidity or oxygen) on oxide transistor is of importance because it might affect the transistor performance. To remove this environmental condition, we performed vacuum seasoning before the deposition of hybrid passivation layer and acquired improved stability. It was found that vacuum seasoning can remove the back channel contamination if a-IGZO film. Therefore, to achieve highly stable oxide TFTs we suggest that adsorbed chemical gas molecules have to be eliminated from the back-channel prior to forming the passivation layers.

• Journal of IKEEE
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• v.22 no.1
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• pp.209-212
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• 2018

In this work, we developed P(VDF-TrFE) organic/ferroelectric material based metal-ferroelectric-metal (MFM) capacitors in order to improve the switching characteristics of gallium nitride (GaN) heterojunction field-effect transistors (HFET). The 27 nm-thick P(VDF-TrFE) MFM capacitors exhibited about 60 ~ 96 pF capacitance with a polarization density of $6{\mu}C/cm^2$ at 4 MV/cm. When the MFM capacitor was connected in series with the gate electrode of GaN HFET, the subthreshold slope decreased from 104 to 82 mV/dec.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1763-1768
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• 2016

This paper presents the electrical characteristics of the gallium nitride (GaN) current aperture vertical electron transistor (CAVET) by using two-dimensional (2-D) technology computer-aided design (TCAD) simulations. The CAVETs are considered as the alternative device due to their high breakdown voltage and high integration density in the high-power applications. The optimized design for the CAVET focused on the electrical performances according to the different gate-source length ($L_{GS}$) and aperture length ($L_{AP}$). We analyze DC and RF parameters inducing on-state current ($I_{on}$), threshold voltage ($V_t$), breakdown voltage ($V_B$), transconductance ($g_m$), gate capacitance ($C_{gg}$), cut-off frequency ($f_T$), and maximum oscillation frequency ($f_{max}$).

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.307.1-307.1
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• 2016

Amorphous zinc tin oxide (ZTO) thin films are being widely studied for a variety electronic applications such as the transparent conducting oxide (TCO) in the field of photoelectric elements and thin film transistors (TFTs). Thin film transistors (TFTs) with transparent amorphous oxide semiconductors (TAOS) represent a major advance in the field of thin film electronics. Examples of TAOS materials include zinc tin oxide (ZTO), indium gallium zinc oxide (IGZO), indium zinc oxide, and indium zinc tin oxide. Among them, ZTO has good optical and electrical properties (high transmittance and larger than 3eV band gap energy). Furthermore ZTO does not contain indium or gallium and is relatively inexpensive and non-toxic. In this study, ZTO thin films were formed by UHV RF magnetron co-sputter deposition on silicon substrates and sapphires. The films were deposited from ZnO and SnO2 target in an RF argon and oxygen plasma. The deposition condition of ZTO thin films were controlled by RF power and post anneal temperature using rapid thermal annealing (RTA). The deposited and annealed films were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), ultraviolet and visible light (UV-VIS) spectrophotometer.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.203-203
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• 2015

Gallium Oxide (Ga2O3) has been widely investigated for the optoelectronic applications due to its wide bandgap and the optical transparency. Recently, with the development of fabrication techniques in nanometer scale semiconductor materials, there have been an increasing number of extensive reports on the synthesis and characterization of Ga2O3 nano-structures such as nano-wires, nano-belts, and nano-dots. In contrast to typical vapor-liquid-solid growth mode with metal catalysts to synthesis 1-dimensional nano-wires, there are several difficulties in fabricating the nano-structures by using sputtering techniques. This is attributed to the fact that relatively low growth temperatures and higher growth rate compared with chemical vapor deposition method. In this study, Ga2O3 nanowires (NWs) were synthesized by using radio-frequency magnetron sputtering method. The NWs were then coated by Au thin films and annealed under Ar or N2 gas enviroment with no supply of Gallium and Oxygen source. Several samples were prepared with varying the post annealing parameters such as gas environment annealing time, annealing temperature. Samples were characterized by using XRD, SEM, and PL measurements. In this presentation, the details of fabrication process and physical properties of branched Ga2O3 NWs will be reported.

• Korean Journal of Materials Research
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• v.15 no.5
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• pp.348-352
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• 2005

Gallium oxyhydroxide (GaOOH) powders were heat-treated in a flowing ammonia gas to form GaN, and the reaction kinetics of the oxide to nitride was quantitatively determined by X-ray diffraction analysis. GaOOH turned into intermediate mixed phases of $\alpha-\;and\;\beta-Ga_2O_3$, and then single phase of GaN. The reaction time for full conversion $(t_c)$ decreased as the temperature increased. There were two-types of rapid reaction processes with the reaction temperature in the initial stage of nitridation at below $t_c$, and a relatively slow processes followed over $t_c$ does not depends on temperatures. The nitridation process was found to be limited by the rate of an interfacial reaction with the reaction order n value of 1 at $800^{\circ}C$ and by the diffusion-limited reaction with the n of 2 at above $1000^{\circ}C$, respectively, at below $t_c$. The activation energy for the reaction was calculated to be 1.84 eV in the temperature of below $830^{\circ}C$, and decreased to 0.38 eV above $830^{\circ}C$. From the comparative analysis of data, it strongly suggest the rate-controlling step changed from chemical reaction to mass transport above $830^{\circ}C$.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.268-272
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• 2011

Due to their novel properties, GaN based semiconductors and their nanostructures are promising components in a wide range of nanoscale device applications. In this work, the gallium nitride is deposited on c-axis oriented sapphire and porous SWCNT substrates by molecular beam epitaxy using a novel single source precursor of $Me_2Ga(N_3)NH_2C(CH_3)_3$ with ammonia as an additional source of nitrogen. The advantage of using a single molecular precursor is possible deposition at low substrate temperature with good crystal quality. The deposition is carried out in a substrate temperature range of 600-750$^{\circ}C$. The microstructural, structural, and optical properties of the samples were analyzed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and photoluminescence. The results show that substrate oriented columnar-like morphology is obtained on the sapphire substrate while sword-like GaN nanorods are obtained on porous SWCNT substrates with rough facets. The crystallinity and surface morphology of the deposited GaN were influenced significantly by deposition temperature and the nature of the substrate used. The growth mechanism of GaN on sapphire as well as porous SWCNT substrates is discussed briefly.

• Journal of Korean Neurosurgical Society
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• v.29 no.11
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• pp.1514-1518
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• 2000

Aspergillosis is an uncommon form of fungal infection of the central nervous system in immunocompetent patient, especially those involving the pituitary gland. Several cases of pituitary aspergillosis have been reported, but most of them are directly invaded from aspergillosis of sphenoid sinus. In the present case, a woman with primary pituitary aspergillosis had neither evidence of infection of the sphenoid sinus nor immunodeficiency. The patient underwent a transsphenoidal surgery for a presumed pituitary tumor. Histopathology demonstrated typical findings of aspergillosis. Postoperatively, amphotericin-B was administered and Gallium-67 scan was performed. We describe a case of primary pituitary aspergillosis mimicking pituitary tumor.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1270_1271
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• 2009

In this research, gallium-incorporated zinc oxide (ZnO:Ga) thin films have been used as a coating material for enhancing the field-emission property of CNT-emitters. Multi-walled CNTs were directly grown on conical-type ($250{\mu}m$ in diameter) metal-tip substrates at $700^{\circ}C$ by inductively coupled plasma-chemical vapor deposition (ICP-CVD). The pulsed laser deposition (PLD) technique was used to produce 5wt% gallium-doped ZnO (5GZO) films with very low stress. The structural properties of ZnO and 5GZO coated CNTs were characterized by Raman spectroscopy. Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) were also used to monitor the variation in the morphology and microstructure of CNTs before and after 5GZO-coating. The measurement of the field emission characteristics showed that the emitter that coated the 5GZO (10nm) on CNTs exhibited the best performance: a maximum emission current of $325{\mu}A$, a threshold field of 2.2 V/${\mu}m$.