ICP(Inductively Coupled Plasma) 처리에 따른 n-type SiGe/Metal contact의 SBH(Schottky Barrier Height) 연구

김이곤,장호원,전창민,송영주,강진영,심규환,제정호,이종람 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.2

The effect of surface treatment of n-type SiGe using the inductively coupled plasma (ICP) was studied by current-voltage and x-ray photoemission spectroscopy measurements. The ICP treatment produced surface oxides and point defects at the surface of SiGe. The x-ray photoemission spectroscopy measurements showed that atomic ratio of Ge/Si was increased after the etching treatment. These results provide the evidence that Si vacancies were produced at the etched surface. Si vacancies acting as donor for electrons resulted in shift of Fermi level to near the conduction band. As a result, Fermi level could be pinned at such Si vacancies, leading to the remarkable reduction of Schottky barrier height and the reduced dependence of Schottky barrier height on metal work function. (Received September 7, 2004)

A GaAs Power MESFET Operating at 3.3V Drain Voltage for Digital Hand-Held Phone

Lee, Jong-Lam,Kim, Hae-Cheon,Mun, Jae-Kyung,Kwon, Oh-Seung,Lee, Jae-Jin,Hwang, In-Duk,Park, Hyung-Moo Electronics and Telecommunications Research Instit 1995 ETRI Journal Vol.16 No.4

A GaAs power metal semiconductor field effect transistor (MESFET) operating at a voltage as low as 3.3V has been developed with the best performance for digital handheld phone. The device has been fabricated on an epitaxial layer with a low-high doped structure grown by molecular beam epitaxy. The MESFET, fabricated using $0.8{\mu}m$ design rule, showed a maximum drain current density of 330 mA/mm at $V_{gs}$ =0.5V and a gate-to-drain breakdown volt-age of 28 V. The MESFET tested at a 3.3 V drain bias and a 900 MHz operation frequency displayed an output power of 32.5-dBm and a power added efficiency of 68%. The associate power gain at 20 dBm input power and the linear gain were 12.5dB and 16.5dB, respectively. Two tone testing measured at 900.00MHz and 900.03MHz showed that a third-order intercept point is 49.5 dBm. The power MESFET developed in this work is expected to be useful as a power amplifying device for digital hand-held phone because the high linear gain can deliver a high power added efficiency in the linear operation region of output power and the high third-order intercept point can reduce the third-order intermodulation.

OPTIMUM BUFFER STRUCTURE OF LOW-HIGH DOPED GaAs MESFET's GROWN BY MOLECULAR BEAM EPITAXY

Lee, Jae-Jin,Lee, Hae-Gwon,Hong, Sang-Ki,Hong, Song-Cheol,Lee, Jong-Lam,Pyun, Kwang-Eui 한국재료학회 1995 Fabrication and Characterization of Advanced Mater Vol.2 No.e4

To improve the microwave performance of low-high doped GaAs MESFET, various type buffer structures were grwon on semi-insulating GaAs substrate by Molecular Beam Epitaxy(MBE). We found that AlGaAs/GaAs superlattice layer in the buffer affected the devices to have better performeances such as large source-to-drain resistance, small knee voltage and larger gain flatness. Also it was demonstrated that the thickness of intrinsic GaAs spacer layer between AlGaAs/GaAs superlatttice and active channel layer must be carefully seleceted(between 50nm~100nm) to have low knee voltage and better gain flatness.

위성자료를 이용한 중국과 몽골 사막주변의 식생수분상태 모니터링

이가람 ( Ga Lam Lee ),김영섭 ( Young Seup Kim ),한경수 ( Kyoung Soo Han ),이창석 ( Chang Suk Lee ),염종민 ( Jong Min Yeom ) 한국지리정보학회 2008 한국지리정보학회지 Vol.11 No.4

기후 시스템에서 지구온난화는 세계적으로 매우 중요한 문제이고 이는 기후변화, 이상기온, 폭우, 가뭄 등의 문제를 초래한다. 특히 가뭄은 기후변화에 의해 여러 해 동안 진행되어온 사막화를 가속화시킨다. 본 연구의 목적은 중국과 몽골 사막주변의 식생수분상태를 탐지하는 것이다. 본 연구에서는 중국과 몽골 사막 주변의 식생수분지수를 산출하기 위해 1999년부터 2006년까지의 SPOT/VEGETATION 위성 이미지를 이용하여 정규수분지수(NDWI: Normalized Difference Water Index)를 산출하였다. 건조한 상태의 식생은 사막화되기 쉽기 때문에 식생 수분은 사막화의 중요한 지표이다. SPOT/VEGETATION 위성영상의 근적외밴드(NIR)와 단파적외밴드(SWIR)의 밴드간 연산을 통하여 NDWI를 구하여 식생의 수분입자를 측정하였다. 그 결과 1999년부터 2006년까지의 NDWI는 사막주변영역에서 감소하는 경향을 보였고, 그 영역은 몽골 고비사막 북동지역과 중국 타클라마칸 사막의 남동지역에 위치해 있었다. Recently, global warming for climate system is a crucial issue over the world and it brings about severe climate change, abnormal temperature, a downpour, a drought, and so on. Especially, a drought over the earth surface accelerates desertification which has been advanced over the several years mainly originated from a climatic change. The objective of this study is to detect variation of vegetation water condition around China and Mongolia desert by using satellite data having advantage in observing surface biological system. In this study, we use SPOT/VEGETATION satellite image to calculate NDWI (Normalized Difference Water Index) around study area desert for monitoring of status of vegetation characteristics. The vegetation water status index from remotely sensing data is related to desertification since dry vegetation is apt to desertify. We can infer vegetation water status using NDWI acquired by NIR (Near infrared) and SWIR (Short wave infrared) bands from SPOT/VGT. The consequence is that NDWI decreased around desert from 1999 to 2006. The areas that NDWI was decreased are located in the northeast of Mongolian Gobi desert and the southeast of China Taklamakan desert.

Three-Dimensional Nanostructured Indium-Tin-Oxide Electrodes for Enhanced Performance of Bulk Heterojunction Organic Solar Cells

Kwon, Hyunah,Ham, Juyoung,Kim, Dong Yeong,Oh, Seung Jae,Lee, Subin,Oh, Sang Ho,Schubert, E. Fred,Lim, Kyung-Geun,Lee, Tae-Woo,Kim, Sungjun,Lee, Jong-Lam,Kim, Jong Kyu Wiley Blackwell (John Wiley Sons) 2014 ADVANCED ENERGY MATERIALS Vol.4 No.7

<P>A three-dimensional indium tin oxide (ITO) nanohelix (NH) array is presented as a multifunctional electrode for bulk heterojunction organic solar cells for simultaneously improving light absorption and charge transport from the active region to the anode. It is shown that the ITO NH array, which is easily fabricated using an oblique-angle-deposition technique, acts as an effective antireflection coating as well as a light-scattering layer, resulting in much enhanced light harvesting. Furthermore, the larger interfacial area between the electrode and the active layer, together with the enhanced carrier mobility through highly conductive ITO NH facilitate transport and collection of charge carriers. The optical and electrical improvements enabled by the ITO NH electrode result in a 10% increase in short-circuit current density and power-conversion efficiency of the solar cells.</P>

Flexible Near-Field Wireless Optoelectronics as Subdermal Implants for Broad Applications in Optogenetics

Shin, Gunchul,Gomez, Adrian M.,Al-Hasani, Ream,Jeong, Yu Ra,Kim, Jeonghyun,Xie, Zhaoqian,Banks, Anthony,Lee, Seung Min,Han, Sang Youn,Yoo, Chul Jong,Lee, Jong-Lam,Lee, Seung Hee,Kurniawan, Jonas,Tureb Elsevier 2017 Neuron Vol.93 No.3

<P><B>Summary</B></P> <P>In vivo optogenetics provides unique, powerful capabilities in the dissection of neural circuits implicated in neuropsychiatric disorders. Conventional hardware for such studies, however, physically tethers the experimental animal to an external light source, limiting the range of possible experiments. Emerging wireless options offer important capabilities that avoid some of these limitations, but the current size, bulk, weight, and wireless area of coverage is often disadvantageous. Here, we present a simple but powerful setup based on wireless, near-field power transfer and miniaturized, thin, flexible optoelectronic implants, for complete optical control in a variety of behavioral paradigms. The devices combine subdermal magnetic coil antennas connected to microscale, injectable light-emitting diodes (LEDs), with the ability to operate at wavelengths ranging from UV to blue, green-yellow, and red. An external loop antenna allows robust, straightforward application in a multitude of behavioral apparatuses. The result is a readily mass-producible, user-friendly technology with broad potential for optogenetics applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Subdermal, wireless optogenetic platform for untethered neuronal control </LI> <LI> Thin, flexible devices for discrete spatio-temporal targeting of neural circuits </LI> <LI> Low-cost, reliable NFC technology adaptable to most common behavioral contexts </LI> <LI> NFC devices can be tailored for use with different wavelength opsins in vivo </LI> </UL> </P>

Symmetrical Emission Transparent Organic Light-Emitting Diodes With Ultrathin Ag Electrodes

Lee, Illhwan,Kim, Sungjun,Park, Jae Yong,Kim, Sungjoo,Cho, Hyung Won,Ham, Juyoung,Gim, Seungo,Kim, Kisoo,Hong, Kihyon,Lee, Jong-Lam IEEE 2018 IEEE photonics journal Vol.10 No.3

<P>This paper describes a way to implement a transparent electrode for symmetrical emission from the bottom and top sides of transparent organic light-emitting diodes (TOLEDs). An ultrathin (∼6 nm) and smooth Ag film was achieved by using the pretreatment of using oxygen plasma prior to deposition of a nanoscale-thin Ag film on glass. The treatment increased the surface energy, thereby enhancing the wettability of the Ag on glass substrate and consequently leading to the formation of thin and unifrom Ag film with high optical transmittance <I>T</I> ∼ 76% and low sheet resistance <I>R</I><SUB>S</SUB> < 15 Ω □<SUP>−1</SUP>. Using this scheme, a highly transparent glass/Ag/WO<SUB>3</SUB> structure with <I>T</I> = 85.6%, and <I>R</I><SUB>S</SUB> = 9.3 Ω □<SUP>−1</SUP> was designed (ITO: 83.1%, 10 Ω □<SUP>−1</SUP>). We conducted finite-domain time-difference simulation for this glass/Ag/WO<SUB>3</SUB> electrode to design a weak microcavity structure that retained the transparency and emitting properties. This optimized structure of TOLEDs (Ag = 6 nm) showed higher <I>T</I> = 73.84% than those of ITO devices (<I>T</I> = 73.19%), and can induce the weak microcavity effect, resuting in improved electroluminescent properties and increased the luminance value from 38.25 to 56.25 cd A<SUP>−1</SUP> at 25 mA cm<SUP>–2</SUP>.</P>

Effects of Physical Treatment of ITO Electrodes on the Electrical Properties of Pentacene Thin-Film Transistors

Lee, Hwa Sung,Cho, Jeong Ho,Kim, Woong-Kwon,Lee, Jong-Lam,Cho, Kilwon The Electrochemical Society 2007 Electrochemical and solid-state letters Vol.10 No.8

Highly-sensitive and highly-correlative flexible motion sensors based on asymmetric piezotronic effect

Lee, Jae Won,Ye, Byeong Uk,Wang, Zhong Lin,Lee, Jong-Lam,Baik, Jeong Min Elsevier 2018 Nano energy Vol.51 No.-

<P><B>Abstract</B></P> <P>This paper describes two highly-sensitive flexible motion sensors (piezoelectric nanogenerators and ultraviolet light emitting diodes based flexible GaN) based on asymmetric polarization created across flexible GaN film and very high correlations of the sensors for precise motion measurement. The operation mechanism is based on piezotronic effect using polarization charges at the interface for tuning the electronic and optoelectronic processes. The nanogenerator showed very high sensitivity (<I>S</I> = 93 at 0.45% under concave bending) and the convex bending led to the decrease of the sensitivity to 24. The electroluminescence intensity also almost linearly decreased with the change of the bending direction, clearly shown in the confocal scanning electroluminescence microscopy images with the bending motion. The two sets of measures showed very high correlations (<I>R</I> <SUP>2</SUP> = 0.98 and 0.96 under concave and convex bending, respectively) with very sensitive directional information. This approach makes to recognize the direction of bending as well as to measure the magnitude of the strain for realizing multi-functional, motion detection sensing devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two highly-sensitive flexible motion sensors (piezoelectric nanogenerators and UV-LEDs based on GaN) has been demonstrated. </LI> <LI> The operation mechanism is based on piezotronic effect using asymmetric polarization charges at the interface. </LI> <LI> The nanogenerator shows very high sensitivity (<I>S</I> = 93 at 0.45%) under concave bending. </LI> <LI> The electroluminescence intensity of Flexible LEDs linearly increased as it was bent from convex to concave bending motion. </LI> <LI> The two sets of measures show very high correlations with very sensitive directional information. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The table of contents entry: Here, for the first time, we describe a strategy to recognize the direction of bending as well as to measure the magnitude of the strain for realizing multi-functional, motion detection sensing devices. The operation mechanism is based on piezotronic effect using asymmetric polarization charges at the interface, which makes it possible to fabricate highly-sensitive two motion sensors. The two sets of measures show very high correlations (<I>R</I> <SUP>2</SUP> = 0.98 and 0.96 under concave and convex bending, respectively) with very sensitive directional information.</P> <P>[DISPLAY OMISSION]</P>

Optical Enhancement in Optoelectronic Devices Using Refractive Index Grading Layers

Lee, Illhwan,Park, Jae Yong,Gim, Seungo,Kim, Kisoo,Cho, Sang-Hwan,Choi, Chung Sock,Song, Seung-Yong,Lee, Jong-Lam American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.5

<P>We enhanced the optical transmittance of a multilayer barrier film by inserting a refractive index grading layer (RIGL). The result indicates that the Fresnel reflection, induced by the difference of refractive indices between SixNy and SiO2, is reduced by the RIGL. To eliminate the Fresnel reflection while maintaining high transmittance, the optimized design of grading structures with the RIGL was conducted using an optical simulator. With the RIGL, we achieved averaged transmittance in the visible wavelength region by 89.6%. It is found that the optimized grading structure inserting the multilayer barrier film has a higher optical transmittance (89.6%) in the visible region than that of a no grading sample (82.6%). Furthermore, luminance is enhanced by 14.5% (from 10 190 to 11 670 cd m(-2) at 30 mA cm(-2)) when the grading structure is applied to organic light-emitting diodes. Finally, the results offer new opportunities in development of multilayer barrier films, which assist industrialization of very cost-effective flexible organic electronic devices.</P>