• Journal of the Korean Physical Society
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• v.73 no.12
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• pp.1867-1872
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• 2018

This study proposes a route for surface modification for p-type cobalt oxide-based gas sensors. We deposit a thin layer of Ni on the Co oxide film by sputtering process and annealed at $350^{\circ}C$ for 15 min in air, which changes a typical sputtered film surface into one interlaced with a high density of hemispherical nanoparticles. Our in-depth materials characterization using transmission electron microscopy discloses that the microstructure evolution is the result of an extensive inter-diffusion of Co and Ni, and that the nanoparticles are nickel oxide dissolving some Co. Sensor performance measurement unfolds that the surface modification results in a significant sensitivity enhancement, nearly 200% increase for toluene (at $250^{\circ}C$) and CO (at $200^{\circ}C$) gases in comparison with the undoped samples.

• Korean Journal of Materials Research
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• v.28 no.4
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• pp.214-220
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• 2018

We report on the fabrication and photoelectrochemical(PEC) properties of a $Cu_2O$ thin film/ZnO nanorod array oxide p-n heterojunction structure with ZnO nanorods embedded in $Cu_2O$ thin film as an efficient photoelectrode for solar-driven water splitting. A vertically oriented n-type ZnO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type $Cu_2O$ thin film was directly electrodeposited onto the vertically oriented ZnO nanorods array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were characterized using X-ray diffraction and scanning electron microscopy as well as Raman scattering. The PEC properties of the fabricated $Cu_2O/ZnO$ p-n heterojunction photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the $Cu_2O/ZnO$ photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., $0.77mA/cm^2$ at 0.5 V vs $Hg/HgCl_2$ in a $1mM\;Na_2SO_4$ electrolyte, revealing an effective operation of the oxide heterostructure. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs $Hg/HgCl_2$, which made the device self-powered. The observed PEC performance was attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential, including the light absorption and separation processes of photoinduced charge carriers.

• Korean Journal of Materials Research
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• v.26 no.2
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• pp.84-89
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• 2016

We present the rectifying and nitrogen monoxide (NO) gas sensing properties of an oxide semiconductor heterostructure composed of n-type zinc oxide (ZnO) and p-type copper oxide thin layers. A CuO thin layer was first formed on an indium-tin-oxide-coated glass substrate by sol-gel spin coating method using copper acetate monohydrate and diethanolamine as precursors; then, to form a p-n oxide heterostructure, a ZnO thin layer was spin-coated on the CuO layer using copper zinc dihydrate and diethanolamine. The crystalline structures and microstructures of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy. The observed current-voltage characteristics of the p-n oxide heterostructure showed a non-linear diode-like rectifying behavior at various temperatures ranging from room temperature to $200^{\circ}C$. When the spin-coated ZnO/CuO heterojunction was exposed to the acceptor gas NO in dry air, a significant increase in the forward diode current of the p-n junction was observed. It was found that the NO gas response of the ZnO/CuO heterostructure exhibited a maximum value at an operating temperature as low as $100^{\circ}C$ and increased gradually with increasing of the NO gas concentration up to 30 ppm. The experimental results indicate that the spin-coated ZnO/CuO heterojunction structure has significant potential applications for gas sensors and other oxide electronics.

• Korean Journal of Materials Research
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• v.26 no.4
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• pp.222-227
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• 2016

Tin oxides have been studied for various applications such as gas detecting materials, transparent electrodes, transparent devices, and solar cells. p-type SnO is a promising transparent oxide semiconductor because of its high optical transparency and excellent electrical properties. In this study, we fabricated p-type SnO thin film using rf magnetron sputtering with an SnO/Sn composite target; we examined the effects of various oxygen flow rates on the SnO thin films. We fundamentally investigated the structural, optical, and electrical properties of the p-type SnO thin films utilizing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis spectrometry, and Hall Effect measurement. A p-type SnO thin film of $P_{O2}=3%$ was obtained with > 80% transmittance, carrier concentration of $1.12{\times}10^{18}cm^{-3}$, and mobility of $1.18cm^2V^{-1}s^{-1}$. With increasing of the oxygen partial pressure, electrical conductivity transition from p-type to n-type was observed in the SnO crystal structure.

• Journal of Sensor Science and Technology
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• v.30 no.5
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• pp.295-299
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• 2021

In this study, we present a complementary metal-oxide-semiconductor (CMOS) binary image sensor. It can shoot an object rotating at a high-speed by using a gate/body-tied (GBT) p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET)-type photodetector. The GBT PMOSFET-type photodetector amplifies the photocurrent generated by light. Therefore, it is more sensitive than a standard N+/P-substrate photodetector. A binary operation is installed in a GBT PMOSFET-type photodetector with high-sensitivity characteristics, and the high-speed operation is verified by the output image. The binary operations circuit comprise a comparator and memory of 1- bit. Thus, the binary CMOS image sensor does not require an additional analog-to-digital converter. The binary CMOS image sensor is manufactured using a standard CMOS process, and its high- speed operation is verified experimentally.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.87-87
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• 2011

Oxide semiconductors are attractive materials for thin-film electronics and optoelectronics due to compatibility with synthesis on large-area, glass and flexible substrate. However, development of thin-film electronics has been hampered by the limited number of semiconducting oxides that are p-type. We report on the effect of the oxygen partial pressure ratio in the gas mixture on the electrical and optical properties of spinel Mg:$ZnCo_2O_4$ thin films deposited at room temperature using RF sputtering, that exhibit p-type conduction. The thin-films are deposited at room temperature in a background of oxygen using a polycrystalline Mg:$ZnCo_2O_4$ ablation target. The p-type conduction is confirmed by positive Seebeck coefficient and positive Hall coefficient. The electrical resistivity and carrier concentration in on dependent Mg:$ZnCo_2O_4$ thin films were found to be dependent on the oxygen partial pressure ratio. As a result, it is revealed that the Mg:$ZnCo_2O_4$ thin-films were greatly influenced on the electrical and optical properties by the oxygen partial pressure condition. The visible region of the spectrum of 36~85%, and hole mobility of 1.1~3.7 $cm^2$/Vs, were obtained.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.239.2-239.2
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• 2016

Numerous studies and approaches have been performed for solar cells to improve their photoelectric conversion efficiencies. Among them, the study for electrode containing transparent conducting oxide (TCO) layers is one of issues as well as for the cell structure based on band theory. In this study, we focused on an interfacial layer between p-type silicon and indium tin oxide (ITO) well-known as TCO materials. According to current-voltage characteristics for the sample with the interfacial layers, the improvement of band alignment between p-type silicon and ITO was observed, and their ohmic properties were enhanced in the proper condition of deposition. To investigate cause of this improvement, spectroscopic ellipsometry and ultraviolet photoelectron spectroscopy were utilized. Using these techniques, band alignment and defect in the band gap were examined. The major materials of the interfacial layer are vanadium oxide and tungsten oxide, which are notable as a hole transfer layer in the organic solar cells. Finally, the interfacial layer was applied to silicon solar cells to see the actual behavior of carriers in the solar cells. In the case of vanadium oxide, we found 10% of improvement of photoelectric conversion efficiencies, compared to solar cells without interfacial layers.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.114-118
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• 2021

In this study, the sensitivity of an active pixel sensor (APS) was adjusted by employing a gate/body-tied (GBT) p-channel metal-oxide semiconductor field-effect transistor (PMOSFET)-type photodetector with a transfer gate. A GBT PMOSFET-type photodetector can amplify the photocurrent generated by light. Consequently, APSs that incorporate GBT PMOSFET-type photodetectors are more sensitive than those APSs that are based on p-n junctions. In this study, a transfer gate was added to the conventional GBT PMOSFET-type photodetector. Such a photodetector can adjust the sensitivity of the APS by controlling the amount of charge transmitted from the drain to the floating diffusion node according to the voltage of the transfer gate. The results obtained from conducted simulations and measurements corroborate that, the sensitivity of an APS, which incorporates a GBT PMOSFET-type photodetector with a built-in transfer gate, can be adjusted according to the voltage of the transfer gate. Furthermore, the chip was fabricated by employing the standard 0.35 ㎛ complementary metal-oxide semiconductor (CMOS) technology, and the variable sensitivity of the APS was thereby experimentally verified.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.356-358
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• 2010

Cuprous oxide ($Cu_2O$)를 기초로 하여 산화 박막 트랜지스터에 대하여 연구를 하였다. 일정한 두께의 cuprous oxide ($Cu_2O$) 박막을 조건별로 열처리 공정을 하고 그에 따른 변화를 측정을 하였다. 그 측정한 결과 중 가장 좋은 열처리 조건으로 열 증착 방식(Vacuum Thermal Evaporation)을 사용하여 cuprous oxide ($Cu_2O$) 비정질 산화 박막 트랜지스터를 제작 및 측정했다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.233-240
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• 2023

p-type Tunnel Oxide Passivating Contacts (TOPCon) solar cell is fabricated with a poly-Si/SiO_x structure. It simultaneously achieves surface passivation and enhances the carriers' selective collection, which is a promising technology for conventional solar cells. The quality of passivation is depended on the quality of the tunnel oxide layer at the interface with the c-Si wafer, which is affected by the bond of SiO formed during the subsequent annealing process. The highest cell efficiency reported to date for the laboratory scale has increased to 26.1%, fabricated by the Institute for Solar Energy Research. The cells used a p-type float zone silicon with an interdigitated back contact (IBC) structure that fabricates poly-Si and SiO_x layer achieves the highest implied open-circuit voltage (iV_oc) is 750 mV, and the highest level of edge passivation is 40%. This review presents an overview of p-type TOPCon technologies, including the ultra-thin silicon oxide layer (SiO_x) and poly-silicon layer (poly-Si), as well as the advancement of the SiO_x and poly-Si layers. Subsequently, the limitations of improving efficiency are discussed in detail. Consequently, it is expected to provide a basis for the simplification of industrial mass production.