Papers by Author: Sung Jae Joo

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Authors: In Ho Kang, Sung Jae Joo, Wook Bahng, Sang Cheol Kim, Nam Kyun Kim
Abstract: The 50W Quasi-resonant mode SMPS which adopted a normally-on-type SiC JFET as a switch has been designed and characterized. A simple decision circuit and an auxiliary power supply was utilized to safely protect the JFET from an in-rush current at initial operation stage and to provide sufficient negative voltage for a complete JFET drive. Even without a refine engineering, the SMPS showed 96% efficiency at a full load state.
Authors: In Ho Kang, Jae Yeol Song, Sung Jae Joo, Wook Bahng, Sang Cheol Kim, Nam Kyun Kim
Abstract: The effect of the doping concentration and space of both p-grid and FLR on the electrical performances of 4H-SiC JBS diode has been investigated. A 4H-SiC JBS diode with the p-grid space of 3um, the FLR space of 3um, and the doping concentration of 5E18cm-3 showed the highest blocking voltage of 1500V.
Authors: Ji Chul Jung, Ji Hong Kim, Kang Min Do, Byung Moo Moon, Sung Jae Joo, Wook Bahng, Sang Cheol Kim, Nam Kyun Kim, Sang Mo Koo
Abstract: We investigated the effect of the substrate temperature on the electrical and the optical properties of ZnO/4H-SiC structures. The n-type ZnO layer was grown on p-type 4H-SiC substrate by pulsed laser deposition to form p-n hetero-junction diode structure. The n-type ZnO thin films were deposited by pulsed laser deposition at different temperatures of 200, 400, and 600 °C, respectively. It was shown from transmission line method (TLM) and auger electron spectroscopy (AES) data that the sheet resistance of ZnO on SiC was increases from ~760 Ω/square to ~4000 Ω/square as the deposition temperature increases and the oxygen outdiffusion decreases. The I-V characteristics with and without illumination has also been studied.
Authors: Jung Ho Lee, Ji Hong Kim, Kang Min Do, Byung Moo Moon, Sung Jae Joo, Wook Bahng, Sang Cheol Kim, Nam Kyun Kim, Sang Mo Koo
Abstract: The characteristics of Ga-doped zinc oxide (GaZnO) thin films deposited at different substrate temperatures (TS~250 to 550oC) on 4H-SiC have been investigated. Structural and electrical properties of GaZnO thin film on n-type 4H-SiC (100)were investigated by using x-ray diffraction, atomic force microscopy (AFM), Hall effect measurement, and Auger electron spectroscopy (AES). Hall mobility is found to increase as the substrate temperature increase from 250 to 550 oC, whereas the lowest resistivity (~3.3 x 10-4 Ωcm) and highest carrier concentration (~1.33x1021cm-3) values are observed for the GaZnO films deposited at 400 oC. It has been found that the c-axis oriented crystalline quality as well as the relative amount of activated Ga3+ Introduction ions may affect the electrical properties of GaZnO films on SiC.
Authors: Wook Bahng, Hui Jong Cheong, In Ho Kang, Seong Jin Kim, Sang Cheol Kim, Sung Jae Joo, Nam Kyun Kim
Abstract: We have investigated the influence of surface modification on the electrical properties of SiC diodes. Schottky diodes (SBDs) as well as PiN diodes were fabricated on n-type SiC substrate with an epilayer, and electrically characterized before and after high temperature annealing, and after removing the surface modified layer, respectively. The devices annealed without graphite cap layer showed ohmic behavior. The surface layer was modified to a conductive layer possibly due to the preferred sublimation of Si species. In order to confirm the existence of modified surface conductive layer, diode was fabricated on the same substrate and electrically characterized after removing 30nm-thick damaged layer by ICP-RIE. The leakage current reduced dramatically, as much as 7 orders of magnitude. The PiN diodes fabricated on the damaged surface layer showed the reverse leakage current and the breakdown voltage of 50mA and 1250V, respectively. While those of the diode fabricated after removing the damaged surface layer were 200nA at the breakdown voltage of 2100V, respectively.
Authors: In Ho Kang, Wook Bahng, Sang Cheol Kim, Sung Jae Joo, Nam Kyun Kim
Abstract: A double delta-doped channel 4H-SiC MESFET is proposed to kick out degradation of the DC and RF performances caused by the surface traps, by forming a quantum-well-like potential well and separating an effective channel from the surface. To obtain an optimum device structure, the DC and RF performances of double delta-doped channel MESFETs having various delta-doping concentrations but the same pinch-off voltage with that of conventional MESFET were also investigated. The SilvacoTM simulation results show that the double delta-doped channel MESFET achieved more improvement of the drain current, the cut-off frequency, and the maximum oscillation frequency for higher delta-doping concentration near the gate. In all cases, DC and RF performances for double delta-doped channel MESFETs are much improved than those of the conventional MESFET.
Authors: In Ho Kang, Wook Bahng, Sung Jae Joo, Sang Cheol Kim, Nam Kyun Kim
Abstract: The effects of post annealing etch process on electrical performances of a 4H-SiC Schottky diodes without any edge termination were investigated. The post etch was carried out using various dry the dry etch techniques such as Inductively Coupled Plasma (ICP) and Neutral Beam Etch (NBE) in order to eliminate suspicious surface damages occurring during a high temperature ion activation process. The leakage current of diodes treated by NBE measured at -100V was about one order lower than that of diode without post etch and a half times lower than that of diode treated by ICP without a significant degradation of forward electrical characteristics. Based on the above results, the post annealing process was adapted to a junction barrier Schottky diode with a field limiting ring. The blocking voltages of diode without post annealing etch and diodes treated by ICP and NBE were -1038V, -1125V, and -1595V, respectively.
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