• Title/Summary/Keyword: photodetector

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Self-developed Efficiency Measurement System of Organic Light-Emitting Diodes (자체 개발한 유기 발광 소자의 효율 측정 시스템)

  • Han, Wone-Keun
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.537-538
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    • 2005
  • A way of measuring an efficiency of organic light-emitting diodes are studied. The efficiency is obtained from the current-voltage-luminance characteristics of the devices. Basically, number of charge carriers are obtained from the current-voltage characteristics, and the number of photons are obtained from the current of Si-photodetector. The organic light-emitting diodes are assumed as a lambertian light source and a program is made for calculating the efficiency. A device structure of ITO/TPD/$Alq_3$/Al is manufactured using thermal-vapor evaporation. This device is set into a measuring system and measured the efficiency. The efficiencies are measured using the lab-made program and commercially available equipments. The obtained values are similar to each other within 10% uncertainty.

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Wireless Digital Signal Transmission using Visible Light Communication with High-Power LEDs

  • Ng, Xiao-Wei;Chung, Wan-Young
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2010.10a
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    • pp.139-140
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    • 2010
  • This paper presents an indoor prototype for wireless digital signal transmission using Visible Light Communications (VLC) in which high power Light Emitting Diode (LED) is used. Using low cost and off-the-shelf components, the transmitter module is constructed using an AVR Atmega128 microcontroller and commercial white beam LEDs. Modulating the light intensity of the LED enables digital signals to be transmitted across the optical link. The receiver module employs a high speed PIN photodetector for optical signal detection and a recovery circuit for optical-electro signal conversion. By sending digitalized data via VLC technology, many applications can be realized in the areas of consumer advertising, traffic safety information and disaster control.

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Performance Comparison of Two Types of Silicon Avalanche Photodetectors Based on N-well/P-substrate and P+/N-well Junctions Fabricated With Standard CMOS Technology

  • Lee, Myung-Jae;Choi, Woo-Young
    • Journal of the Optical Society of Korea
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    • v.15 no.1
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    • pp.1-3
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    • 2011
  • We characterize and analyze silicon avalanche photodetectors (APDs) fabricated with standard complementary metal-oxide-semiconductor (CMOS) technology. Current characteristics, responsivity, avalanche gain, and photodetection bandwidth of CMOS-APDs based on two types of PN junctions, N-well/P-substrate and $P^+$/N-well junctions, are compared and analyzed. It is demonstrated that the CMOS-APD using the $P^+$/N-well junction has higher responsivity as well as higher photodetection bandwidth than N-well/P-substrate. In addition, the important factors influencing CMOS-APD performance are clarified from this investigation.

GaN-based Ultraviolet Passive Pixel Sensor for UV Imager

  • Lee, Chang-Ju;Hahm, Sung-Ho;Park, Hongsik
    • 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.

Technology Trends of Optical Devices and Components for Datacenter Communications (데이터센터 통신용 광소자 및 광부품 기술 동향)

  • Han, Y.T.;Lee, D.H.;Kim, D.J.;Shin, J.U.;Lee, S.Y.;Yun, S.J.;Baek, Y.
    • Electronics and Telecommunications Trends
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    • v.37 no.2
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    • pp.42-52
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    • 2022
  • Intra- and inter- datacenter data traffic is rapidly increasing due to the spread of smart devices, cloud computing, and non-face-to-face services. Recently, 400-Gbps optical transceivers based on 100-Gbps/channel have been released primarily by major overseas companies. Various solutions for next-generation datacenter interconnect are being proposed by international standardization and multiple source agreement groups. Following this trend, ETRI has developed a 400-Gbps optical transmission/reception engine using 100-Gbps/channel light sources and photodetectors as well as a silica-based AWG. In the future, technologies of optical devices and components for intra-datacenter communication are expected to be developed based on a data rate of 200-Gbps/channel. Thus, 1.6-Tbps class optical transceivers will be released.

Photoresponse Properties of Reduced Graphene Oxide/n-silicon Heterojunction Fabricated by the Vacuum Filtration and Transfer Method

  • Du, Yonggang;Qiao, Liangxin;Xue, Dingyuan;Jia, Yulei
    • Current Optics and Photonics
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    • v.6 no.4
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    • pp.367-374
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    • 2022
  • A photodetector based on a reduced graphene oxide (RGO)/n-Si heterojunction with high responsivity, detectivity and fast response speed is presented. Here, we put forward a simple vacuum filtration method to prepare RGO film and transfer it onto an n-Si substrate to form an RGO/n-Si heterojunction. The experimental results show that the heterojunction has good rectification characteristics, and the response and recovery time are less than 0.31 s and 0.25 s, respectively. Under 470 nm light conditions at -2 V applied voltage, the responsivity and detectivity of the device are 65 mA/W and 4.02 × 1010 cmHz1/2W-1, respectively. The simple preparation process and good performance of the RGO/n-Si heterojunction make it a promising material for photoelectric detection, especially in the near-ultraviolet band.

Optical Triangular Waveform Generation with Alterable Symmetry Index Based on a Cascaded SD-MZM and Polarization Beam Splitter-combiner Architecture

  • Dun Sheng Shang;Guang Fu Bai;Jian Tang;Yan Ling Tang;Guang Xin Wang;Nian Xie
    • Current Optics and Photonics
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    • v.7 no.5
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    • pp.574-581
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    • 2023
  • A scheme is proposed to generate triangular waveforms with alterable symmetry. The key component is a cascaded single-drive Mach-Zehnder modulator (SD-MZM) and optical polarization beam splitter-combiner architecture. In this triangular waveform generator, the bias-induced phase shift, modulation index and controllable delay difference are changeable. To generate triangular waveform signals with different symmetry indexes, different combinations of these variables are selected. Compared with the previous schemes, this generator just contains one SD-MZM and the balanced photodetector (BPD) is not needed, which means the costs and energy consumption are significantly reduced. The operation principle of this triangular waveform generator has been theoretically analyzed, and the corresponding simulation is conducted. Based on the theoretical and simulated results, some experiments are demonstrated to prove the validity of the scheme. The triangular waveform signals with a symmetry factor range of 20-80% are generated. Both experiment and theory prove the feasibility of this method.

A Study about the Change of Locations of the Center of Resistance According to the Decrease of Alveolar Bone Heights and Root Lengths during Anterior Teeth Retraction using the Laser Reflection Technique (Laser 반사측정법을 이용한 전치부 후방 견인시 치조골 높이와 치근길이 감소에 따른 저항중심의 위치변화에 관한 연구)

  • Min, Young-Gyu;Hwang, Chung-Ju
    • The korean journal of orthodontics
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    • v.29 no.2 s.73
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    • pp.165-181
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    • 1999
  • Treatment mechanics should be individualized to be suitable for each patient's personal teeth and anatomic environment to get a best treatment result with the least harmful effects to teeth and surrounding tissues. Especially, the change of biomechanical reaction associated with that of the centers of resistance of teeth should be considered when crown-to-root ratio changed due to problematic root resorption and/or periodontal disease during adult orthodontic treatment. At the present study, in order to investigate patterns of initial displacements of anterior teeth under certain orthodontic force when crown-to-root ratio changed in not only normal periodontal condition but also abnormal periodontal and/or teeth condition, the changes of the centers of resistance for maxillary and mandibular 6 anterior teeth as a segment were studied using the laser reflection technique, the lever & pulley force applicator and the photodetector with these quantified variables reducing alveolar bone 2mm by 2mm for each of maxillary 6 anterior teeth until the total amount of 8mm and root 2mm by 2mm for each of mandibular 6 anterior ones until the total amount of 6mm. The results were as follows: 1. Under unreduced condition, the center of resistance during initial displacement of maxillary 6 anterior teeth was located at the point of about $42.4\%$ apically from cemento-enamel junction(CEJ) of the averaged tooth of them and kept shifting to about $76.7\%$ with alveolar bone reduction. 2. The distance from the averaged alveolar crest level of maxillary 6 anterior teeth to the center of resistance for the averaged tooth of them kept decreasing with alveolar bone reduction, but the ratio to length of the averaged root embedded in the alveolar bone was stable at around $33\%$ regardless of that. 3. Under unreduced condition, the center of resistance during initial displacement of mandibular 6 anterior teeth was located at the Point of about $43\%$ apically from CEJ of the averaged tooth of them and this ratio kept increasing to about $54\%$ with root reduction. But the distance from CEJ to the center of resistance decreased from around 5.3mm to around 3.3mm, that is to say, the center of resistance kept shifting toward CEJ with the shortening of root length. 4. A unit reduction of alveolar bone had greater effects on the change of the centers of resistance than that of root did during initial Phase of each reduction. But both of them had similar effects at the middle region of whole length of the averaged root.

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Fabrication and Device Characteristics of Infrared Photodetector Based on InAs/GaSb Strained-Layer Superlattice (InAs/GaSb 응력초격자를 이용한 적외선검출소자의 제작 및 특성 연구)

  • Kim, J.O.;Shin, H.W.;Choe, J.W.;Lee, S.J.;Kim, C.S.;Noh, S.K.
    • Journal of the Korean Vacuum Society
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    • v.18 no.2
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    • pp.108-115
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    • 2009
  • The superlattice infrared photodetector (SLIP) with an active layer of 8/8-ML InAs/GaSb type-II strained-layer superlattice (SLS) of 150 periods was grown by MBE technique, and the proto-type discrete device was defined with an aperture of $200-{\mu}m$ diameter. The contrast profile of the transmission electron microscope (TEM) image and the satellite peak in the x-ray diffraction (XRD) rocking curve show that the SLS active layer keeps abrupt interfaces with a uniform thickness and a periodic strain. The wavelength and the bias-voltage dependences of responsivity (R) and detectivity ($D^*$) measured by a blackbody radiation source give that the cutoff wavelength is ${\sim}5{\mu}m$, and the maximum Rand $D^*$ ($\lambda=3.25{\mu}m$) are ${\sim}10^3mA/W$ (-0.6 V/13 K) and ${\sim}10^9cm.Hz^{1/2}/W$ (0 V/13 K), respectively. The activation energy of 275 meV analyzed from the temperature dependent responsivity is in good agreement with the energy difference between two SLS subblevels of conduction and valence bands (HH1-C) involving in the photoresponse process.

Anomalous Effect of Hydrogenation on the Optical Characterization $In_{0.5}Ga_{0.5}As$ Quantum Dot Infrared Photodetectors (MBE로 성장된 $In_{0.5}Ga_{0.5}As/GaAs$ 양자점 원적외선 수광소자의 수소화 처리가 광학적 특성에 미치는 특이영향)

  • Lim J.Y.;Song J.D.;Choi W.J.;Cho W.J.;Lee J.I.;Yang H.S.
    • Journal of the Korean Vacuum Society
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    • v.15 no.2
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    • pp.223-230
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    • 2006
  • We have investigated the characteristics of hydrogen (H) plasma treated quantum dot infrared photodetectors (QDIPs). The structure used in this study consists of 3 stacked, self assembled $In_{0.5}Ga_{0.5}As/GaAs$ QD layer separated by GaAs barrier layers that were grown by molecular beam epitaxy. Optical characteristics of QDIPs, such as photoluminescence (PL) spectra and photocurrent spectra, have been studied and compared with each other for the as grown and H plasma treated QDIPs. H plasma treatment, resulted in the splitting of PL peak, which can be attributed to the redistribution of the size of QDs. The activation energies estimated from the temperature dependence of integrated PL intensity for as grown and H plasma treated QDIPs are found to be in good agreement with those determined from corresponding peaks of photocurrent spectra. It is also noted that photocurrent is detected up to 130 K for the H plasma treated QDIP, suggesting the future possibility for the development of infrared photodetectors with high temperature operation.