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Cho, Sung Woon,Kim, Da Eun,Kim, Kyung Su,Jung, Sung Hyun,Cho, Hyung Koun The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.40
<▼1><P>ZTO/Al2O3 heterostructure and chemically stable sol–gel multi-stacking method are proposed for practical solution-processed oxide TFTs.</P></▼1><▼2><P>For practical solution-processed oxide thin-film transistors (TFTs) with cost efficiency, high performance, and long-term environmental reliability, we suggested a novel sol–gel processed rare-metal-free oxide-based semiconductor/insulator [ZnSnO (ZTO)/Al2O3] heterostructure channel and chemically stable sol–gel multi-stacking method. In the rare-metal-free ZTO/Al2O3 heterostructure, an In- and Ga-free ZTO semiconductor with high chemical durability is employed as an effective electron transport layer. An earth-abundant Al2O3 insulator is employed as both an ambient gas molecule barrier in the ZTO back-channel region and a tunneling-induced electron transport layer beneath the source/drain electrodes. In order to minimize inevitable chemical attack coming from acidic and basic precursor solutions during the sol–gel based heterostructure construction, chemically stable sol–gel ZTO/Al2O3 heterostructure stacking was successfully demonstrated with a chemically durable Sn-modulated ZTO semiconductor and weakly corrosive pH-engineered Al2O3 precursor solution. The proposed rare-metal-free ZTO/Al2O3 heterostructure and chemically stable stacking realized sol–gel processed oxide TFT with excellent stability under humidity, temperature, bias voltage, and light exposure. We believe that our novel ZTO/Al2O3 heterostructure and chemically stable sol–gel stacking method will provide an interesting route for the fabrication of practical solution-based oxide TFTs with cost efficiency, high performance, and long-term reliability, instead of conventional rare-metal based oxide materials and channel structures with high environmental instability.</P></▼2>
Cho, Sung Woon,Kwon, Sung Min,Lee, Minkyung,Jo, Jeong-Wan,Heo, Jae Sang,Kim, Yong-Hoon,Cho, Hyung Koun,Park, Sung Kyu Elsevier 2019 Nano energy Vol.66 No.-
<P><B>Abstract</B></P> <P>For the realization of low-power consumption brain-inspired neuromorphic computing devices which mimic the biological neuronal information processing methodology, the development of photonic transistors capable of synaptic behaviors and neuronal computation have attracted lots of interests. Here, metal-chalcogenide (MC)/metal-oxide (MO) heterogeneous photonic neuro-transistors capable of multi-spectrum triggered synaptic responses and corresponding neuronal computation were developed for an intelligent and energy efficient neuromorphic device. The photonic transistor architecture including a solution-processed broadband photo-active heterogeneous channel and electronic modulatory terminal enable to establish power-saved multi-level writing/reading processing. The multi-spectral gate-triggerings and their synaptic responses were emulated via the broadband absorbing MC/MO heterogeneous semiconducting structure and its defective hetero-interface, which can be fine-tuned by varying photo-spectrum of applied spikes and controlling of interfacial traps in-between, respectively. More importantly, the multi-spectrum triggered heterogeneous photonic neuro-transistors can facilitate wider dynamic and more intelligent neuronal computation such as multi-level dendritic summation and fire behaviors, logic-computation, and associated learning beyond conventional simple synaptic-level photonic devices. The results reported here argue that the multi-spectral activated heterogeneous photonic neuro-transistor outperforms current state-of-neuro-devices, provide a facile and generic route to achieve high-density and energy efficient neuromorphic system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heterogeneous photonic neuro-transistors capable of multi-spectral neuromorphic computation and low-power operation. </LI> <LI> Heterogeneous channel consists of solution-processed ZnSnO and CdS semiconductors. </LI> <LI> Power-efficient operation was enabled by heterogeneous channel architecture and modulatory terminal. </LI> <LI> All photo-neuromorphic computation dynamics were demonstrated via multi-spectrum gate triggering. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Cho, Sung Woon,Kim, Young Been,Kim, Da Eun,Kim, Kyung Su,Yoon, Young Dae,Kang, Won Jun,Lee, Woobin,Cho, Hyung Koun,Kim, Young Hun Elsevier 2017 Journal of alloys and compounds Vol.714 No.-
<P><B>Abstract</B></P> <P>Individual oxide semiconductors and metals experience unique pH-dependent phase-transition into natively stable phases (metal, metal ions, or oxide phases) in various acidic and basic solutions. Thus, the corrosion behavior of oxide semiconductors and metals can be engineered by controlling pH values. In particular, the specific pH value induced interesting corrosion behavior that oxide semiconductor becomes chemically-stable and metal solely experiences active ionization. First, the pH-dependent corrosion behavior of ternary oxide semiconductors [ZnSnO (ZTO) and InZnO (IZO)] and common metals (Mo and Mo/Cu) was explored based on theoretical Pourbaix diagram and experimental corrosion data. Next, the pH-dependent corrosion behavior based back-channel wet-etch (BCWE) process using pH-controlled wet etchants was designed and applied for chemical damage-, metal residue-, and curing treatment-free solution-processed oxide thin film transistors (TFTs) circuit integration without electrical degradation. Thick-Mo and thin-Mo/thick-Cu could be completely ionized without any metal oxide residues in middle-basic (pH ≥ 10) and weak-acidic (pH = 6) wet-etchants, respectively. Chemically durable ZTO in the broad pH region (6 ≤ pH ≤ 11) indicated sufficient potential as channel candidates for the circuit integration of chemical damage-free oxide TFTs as opposed to IZO (pH = 10). Finally, solution-processed ZTO TFTs could be fabricated with wet-etched Mo and Mo/Cu using the customized wet-etchant condition (pH = 10 and 6) without electrical degradation (current-drop, hump phenomena, or instability) that was inevitably generated in a conventional BCWE.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The ternary zinc tin oxide and indium zinc oxide were synthesized via sol-gel process. </LI> <LI> The pH-dependent corrosion behavior of ternary oxides and common metals was examined. </LI> <LI> Oxide film became stable and metal electrode was solely ionized in specific pH value. </LI> <LI> The pH-dependent corrosion behavior based back-channel wet-etch (BCWE) process was developed. </LI> <LI> The developed BCWE process were applied for solution-processed oxide TFTs integration. </LI> </UL> </P>
저압 MOCVD 방법으로 성장된 lnAlAs 에피층에서 상분리와 규칙 현상의 관찰
조형균(Hyung Koun Cho),이번(Bun Lee),백종협(Jong-Hyeob Baek),한원석(Won Seok Han),이정용(Jeong Yong Lee),권명석(Myoung Seok Kwon) 한국진공학회(ASCT) 1999 Applied Science and Convergence Technology Vol.8 No.3(2)
LP-MOCVD 방법에 의해 InP 기판 위에 성장된 InAlAs 에피층의 상분리와 규칙 현상을 DCXRD, PL, TEM을 이용하여 분석하였다. DCXRD와 PL의 반측폭과 강도로부터 InAlAs 에피층의 구조적, 광학적 품질이 성장 온도가 증가함에 따라 향상되었다. 상분리와 규칙 현상으로 인한 밴드갭의 감소량은 565℃, 615℃, 700℃의 성장 온도에서 각각 291, 246, 28 meV이고 구조적, 광학적 품질과 같은 경향성을 보여주었다. TEM으로부터 상분리 현상은 565℃의 성장 온도에서 가장 강하게 관찰되었고, HRTEM 이미지 사진에서 InAs가 풍부한 영역과 AlAs가 풍부한 영역 사이에 조성 차이로 인하여 약 2˚의 격자 줄무늬의 회전이 발생하였다. 565℃에서 성장된 시편에 대한 RTA 열처리 실험은 880℃에서 3분간의 열처리로 약 78 meV 정도의 밴드갭 증가를 보여주고, TEM을 통해 밴드갭의 증가는 규칙 현상의 완전한 사라짐이라는 것이 관찰되었다. 이 결과는 열처리 전에 발생한 밴드갭 감소량의 3/4가 상분리 현상으로 발생하였다는 결론을 얻을 수 있다. We have studied the phase separation and ordering phenomenon of lnAlAs epilayers grown on InP substrate by LP-MOCVD with DCXRD, PL, and TEM. From the intensity and FWHM of DCXRD and PL, we observed that the structural and optical quality of lnAlAs epilayers were improved as growth temperature increased. The band-gap reduction due to phase separation and ordering is 291, 246, and 28 meV in the InAlAs epilayers grown at 565℃, 615℃, and 700℃, respectively, and shows the same trends as structural and optical quality. The maximum degree of phase separation was obtained by TEM from the lnAlAs epilayer grown at 565℃ in which the HRTEM micrograph showed the lattice fringe between lnAs-rich and AlAs-rich regions was tilted by 2˚ due to composition difference. However, the maximum degree of ordering by intensity of extra spots was obtained at the medium growth temperature. The annealing experiment by RTA of sample grown at 565℃ shows a maximum band-gap shift of 78 meV at 880℃ for 3 min, and TEM shows that the origin of the blue shift of band-gap is the complete disappearance of ordering. Through annealing we can conclude that short time annealing affects only ordering and that most of the total band-gap reduction (~3/4) occurs by phase separation.
Fabrication of nanocrystal ink based superstrate-type CuInS<sub>2</sub> thin film solar cells
Cho, Jin Woo,Park, Se Jin,Kim, Woong,Min, Byoung Koun IOP Pub 2012 Nanotechnology Vol.23 No.26
<P>A CuInS<SUB>2</SUB> (CIS) nanocrystal ink was applied to thin film solar cell devices with superstrate-type configuration. Monodispersed CIS nanocrystals were synthesized by a colloidal synthetic route and re-dispersed in toluene to form an ink. A spray method was used to coat CIS films onto conducting glass substrates. Prior to CIS film deposition, TiO<SUB>2</SUB> and CdS thin films were also prepared as a blocking layer and a buffer layer, respectively. We found that both a TiO<SUB>2</SUB> blocking layer and a CdS buffer layer are necessary to generate photoresponses in superstrate-type devices. The best power conversion efficiency (∼1.45%) was achieved by the CIS superstrate-type thin film solar cell device with 200 and 100 nm thick TiO<SUB>2</SUB> and CdS films, respectively. </P>
Cho, Jin Woo,Ismail, Agus,Park, Se Jin,Kim, Woong,Yoon, Sungho,Min, Byoung Koun American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.10
<P>Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> (CZTS) is a very promising semiconductor material when used for the absorber layer of thin film solar cells because it consists of only abundant and inexpensive elements. In addition, a low-cost solution process is applicable to the preparation of CZTS absorber films, which reduces the cost when this film is used for the production of thin film solar cells. To fabricate solution-processed CZTS thin film using an easily scalable and relatively safe method, we suggest a precursor solution paste coating method with a two-step heating process (oxidation and sulfurization). The synthesized CZTS film was observed to be composed of grains of a size of ∼300 nm, showing an overall densely packed morphology with some pores and voids. A solar cell device with this film as an absorber layer showed the highest efficiency of 3.02% with an open circuit voltage of 556 mV, a short current density of 13.5 mA/cm<SUP>2</SUP>, and a fill factor of 40.3%. We also noted the existence of Cd moieties and an inhomogeneous Zn distribution in the CZTS film, which may have been triggered by the presence of pores and voids in the CZTS film.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-10/am401210w/production/images/medium/am-2013-01210w_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am401210w'>ACS Electronic Supporting Info</A></P>
In vitro and In vivo Evaluation of Novel Gel Formulations of Testosterone for Transdermal Delivery
Sung Koun Heo,Young Seok Cho,Sang Dae Han,Jin Kang Chang,Eun Ju Yoon,Dae Woong Ko,Chang Baeg Lim,Suk Jae Chung,Chang Koo Shim,Dae Duk Kim 韓國藥劑學會 2005 Journal of Pharmaceutical Investigation Vol.35 No.5