• Korean Journal of Materials Research
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• v.30 no.10
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• pp.566-572
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• 2020

In the recent years, thin film solar cells (TFSCs) have emerged as a viable replacement for crystalline silicon solar cells and offer a variety of choices, particularly in terms of synthesis processes and substrates (rigid or flexible, metal or insulator). Among the thin-film absorber materials, SnS has great potential for the manufacturing of low-cost TFSCs due to its suitable optical and electrical properties, non-toxic nature, and earth abundancy. However, the efficiency of SnS-based solar cells is found to be in the range of 1 ~ 4 % and remains far below those of CdTe-, CIGS-, and CZTSSe-based TFSCs. Aside from the improvement in the physical properties of absorber layer, enormous efforts have been focused on the development of suitable buffer layer for SnS-based solar cells. Herein, we investigate the device performance of SnS-based TFSCs by introducing double buffer layers, in which CdS is applied as first buffer layer and ZnMgO films is employed as second buffer layer. The effect of the composition ratio (Mg/(Mg+Zn)) of RF sputtered ZnMgO films on the device performance is studied. The structural and optical properties of ZnMgO films with various Mg/(Mg+Zn) ratios are also analyzed systemically. The fabricated SnS-based TFSCs with device structure of SLG/Mo/SnS/CdS/ZnMgO/AZO/Al exhibit a highest cell efficiency of 1.84 % along with open-circuit voltage of 0.302 V, short-circuit current density of 13.55 mA cm^-2, and fill factor of 0.45 with an optimum Mg/(Mg + Zn) ratio of 0.02.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.117-117
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• 2012

Si:Ge alloy semiconductor nanocrystals (NCs) offer challenging opportunities for integrated optoelectronics/optoplasmonics, since they potentially allow unprecedentedly strong light-matter interaction in the wavelength range of the optical communication. In this talk, we discuss the recent research efforts of my laboratory to develop optoelectronic components based on individual group IV NCs. We present experimental demonstration of the individual NC optoelectronic devices, including broadband Si:Ge nanowire (NW) photodetectors, intra NW p-n diodes, Ge NC electrooptical modulators and near-field plasmonic NW detectors, where the unique size effects at the nanometer scales commonly manifest themselves. In particular, we demonstrated a scanning photocurrent imaging technique to investigate dynamics of photocarriers in individual Si:Ge NWs, which provides spatially and spectrally resolved local information without ensemble average. Our observations represent inherent size-effects of internal gain in semiconductor NCs, thereby provide a new insight into nano optoplasmonics.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.101.1-101.1
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• 2016

Van der Waals (vdW) heterostructures built from two-dimensional layered materials provide an unprecedented opportunity in designing new material systems because the lack of dangling bonds on the vdW surfaces enables the creation of high-quality heterointerfaces without the constraint of atomically precise commensurability. In particular, the ability to build artificial heterostructures, combined with the recent advent of transition metal dichalcogenides, allows the fabrication of unique semiconductor heterostructures in an ultimate thickness limit for fundamental studies as well as novel device applications. In this talk, we will present the characterization of the electronic and optoelectronic properties of atomically thin p-n junctions consisting of vertically stacked WSe2 and MoS2 monolayers. We observed gate-tunable diode-like current rectification and a photovoltaic response across the p-n interface. Unlike conventional bulk p-n junctions, the tunneling-assisted interlayer recombination of the majority carriers is responsible for the tenability of the charge transport and the photovoltaic response. Furthermore, we will discuss the enhanced optoelectronic characteristics in graphene-sandwiched vdW p-n junctions.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.549-556
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• 1994

광전변화소자(Photo electric conversion device)는 광전효과-내부 광전효과(광도전 및 광기전력) 및 외부광전효과(광전자방출)을 이용하여 광을 전기신호로 변화시키는 소자를 광전자소자라 하며, 광전자 및 양자전자공학의 발전과 함께 많은 개발이 되고 있다. 이 광전변환소자는 주로서 고체박막의 재료를 이용하며, 소자의 소형화, 고성능화, 고신뢰성등의 요구와 함께 광전기술연구가 활발하게 진행되고 있다. 현재 광전소자의 광의 파장은 가시부만이 아니고, X선으로 부터 적외선까지에 걸쳐 있다. 이 파장에 대응하여 각종의 단결정이 필요하고, 소자의 설계가 요구된다. 이들의 응용은 소자의 광의 발진, 증폭, 검출의 소자만이 아니고 변조, 편향, 기록, 전달로등 다종다양의 기능을 갖는 소자가 요구되고 있다. 이들의 Optoelectronic Device의 연구가 활발하게 진행되어 새로운 광전소자의 제품이 개발되고 있어, 이에 대한 소개를 하고져 한다.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.68-68
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• 2000

In this paper a very brief review of historical development of optical science and technology in China is presented. More attention has been pain on Modem Optics, which developed since 1950s. The recent development of optical science and technology in following fields are introduced. 1. Optical engineering and instrumentation (tracking theodolites, high speed cameras, satellite laser ranging systems, satellite flying attitude control, cameras for remote sensing, astronomical optical instrument) 2. Applied optics (adaptive optics, optical metrology, infrared optics, optical processing, optical holography) 3. Laser science and technology (ultrashort pulse lasers, UV-X ray lasers, high power laser facilities and laser fusion, laser isotope separation) 4. Laser and nonlinear materials (rare earth elements doped laser glasses and crystals, tunable laser crystals, borate series and organic nonlinear crystals) 5. Optoelectronic science and technology (Optical communication, optical data storage, optical computing) The current situation and developing prospect of optical and optoelectronic industry in China are presented. Furthermore it points out that the optical industry could be developed vigorously only if products development capacity is enhanced and new products industrialization is heightened. The main research and education institutions in the optics field in China, as well as the Chinese Optical Society (COS) are introduced.

• Applied Science and Convergence Technology
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• v.27 no.2
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• pp.42-45
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• 2018

Photovoltaic and optoelectronic devices based on hybrid metal halide perovskites ($MAPbX_3$; $MA=CH_3NH_3{^+}$, $X=Cl^-$, $Br^-$, or $I^-$) are rapidly improving in power conversion efficiency. Also, during recent years, perovskite single crystals have emerged as promising materials for high-efficiency photovoltaic and optoelectronic devices because of their low defect density. Here we show that the light soaking effect of mixed halide perovskite ($MAPbBr_{3-x}I_x$) single crystals can be explained using photoluminescence, time-resolved photoluminescence, and Raman scattering measurements. Unlike Br-based single crystal, Br/I mixed single crystal show a strong light soaking effect under laser irradiation condition that was related to the existence of multiple phases.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.6-6
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• 2011

Graphene, a monlayer of carbon atoms arrange to form a 2-dimensional honeycomb lattice, exhibits enormous fascinating properties, such as a linear energy dispersion relation, a wide-range optical absorption, high thermal conductivity, and mechanical flexibility [1]. Because the unique material properties of graphene allow it to be a promising building block for the next generation electronic and optoelectronic devices, sometimes graphene-based devices have refereed to be a strong candidate to overcome the intrinsic limitations of conventional semiconductor-based technology [2,3]. However, there are several fundamental or technological hurdles to be overcome in real applications of graphene in electronics and optoelectronics. In this tutorial we will present a short introduction to the basic materials properties and recent progress in applications of graphene and discuss future outlook of graphene-based electronic and optoelectronic devices.

• Journal of Sensor Science and Technology
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• v.28 no.3
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• pp.152-156
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• 2019

An ultraviolet (UV) image sensor is an extremely important optoelectronic device used in scientific and medical applications because it can detect images that cannot be obtained using visible or infrared image sensors. Because photodetectors and transistors are based on different materials, conventional UV imaging devices, which have a hybrid-type structure, require additional complex processes such as a backside etching of a GaN epi-wafer and a wafer-to-wafer bonding for the fabrication of the image sensors. In this study, we developed a monolithic GaN UV passive pixel sensor (PPS) by integrating a GaN-based Schottky-barrier type transistor and a GaN UV photodetector on a wafer. Both individual devices show good electrical and photoresponse characteristics, and the fabricated UV PPS was successfully operated under UV irradiation conditions with a high on/off extinction ratio of as high as $10^3$. This integration technique of a single pixel sensor will be a breakthrough for the development of GaN-based optoelectronic integrated circuits.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.241-245
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• 2010

One of the weak points of the Cr-doped SZO is that until now, it has only been fabricated on perovskite substrates, whereas NiO-ReRAM devices have already been deposited on Si substrates. The fabrication of RAM devices on Si substrates is important for commercialization because conventional electronics are based mainly on silicon materials. Cr-doped ReRAM will find a wide range of applications in embedded systems or conventional memory device manufacturing processes if it can be fabricated on Si substrates. For application of the commercial memory device, Cr-doped $SrZrO_3$ perovskite thin films were deposited on a $SrRuO_3$ bottom electrode/Si(100)substrate using pulsed laser deposition. XRD peaks corresponding to the (112), (004) and (132) planes of both the SZO and SRO were observed with the highest intensity along the (112) direction. The positions of the SZO grains matched those of the SRO grains. A well-controlled interface between the $SrZrO_3$:Cr perovskite and the $SrRuO_3$ bottom electrode were fabricated, so that good resistive switching behavior was observed with an on/off ratio higher than $10^2$. A pulse test showed the switching behavior of the Pt/$SrZrO_3:Cr/SrRuO^3$ device under a pulse of 10 kHz for $10^4$ cycles. The resistive switching memory devices made of the Cr-doped $SrZrO_3$ thin films deposited on Si substrates are expected to be more compatible with conventional Si-based electronics.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.20.2-20.2
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• 2011

III-nitrides have attracted much attention for optoelectronic device applications whose emission wavelengths ranging from green to ultraviolet due to their wide band gap. However, due to the strong polarization properties of conventional c-plane III-nitrides, the built-in polarization-induced electric field limits the performance of optical devices. Therefore, there has been a renewed interest in the growth of nonpolar III-nitride semiconductors for polarization free heterostructure optoelectronic and electronic devices. However, the crystal and the optical quality of nonpolar/semipolar GaN have been poorer than those of conventional c-plane GaN, resulting in the relative poor optical and electrical properties of light emitting diodes (LEDs). In this presentation, I will discuss the growth and characterization of high quality nonpolar a-plane and semipolar (11-22) GaN and InGaN multiple quantum wells (MQWs) grown on r- and m-plane sapphire substrates, respectively, by using metalorganic chemical vapor deposition (MOCVD) without a low temperature GaN buffer layer. Especially, the epitaxial lateral overgrowth (ELO) technique will be also discussed to reduce the dislocation density and enhance the performance of nonpolar and semipolar GaN-based LEDs.