Photoconductivity
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Photoresistor – a Detailed Guide
Photoresistor – A Detailed Guide While walking through the streets in the evening, have you ever noticed how the street lights turn on automatically as it starts getting darker? This automatic switching ON of the street lights are due to the presence of a special type of variable resistor on its circuit. The resistance of this variable resistor depends on the amount of light that falls on it. Such a resistor is called the photo-resistor, and in this article we shall discuss about some aspects of the same. So let’s start! What is a Photoresistor? Photoresistor is the combination of words “photon” (meaning light particles) and “resistor”. True to its name, a photo-resistor is a device or we can say a resistor dependent on the light intensity. For this reason, they are also known as light dependent a.k.a. LDRs. So to define a photo-resistor in a single line we can write it as: “Photoresistor is a variable resistor whose resistance varies inversely with the intensity of light” From our basic knowledge about the relationship between resistivity (ability to resist the flow of electrons) and conductivity (ability to allow the flow of electrons), we know that both are polar opposites of each other. Thus when we say that the resistance decreases when intensity of light increases, it simply implies that the conductance increases with increase in intensity of light falling on the photo-resistor or the LDR, owing to a property called photo-conductivity of the material. Hence these Photoresistors are also known as photoconductive cells or just photocell. -
OPTI510R: Photonics
OPTI510R: Photonics Khanh Kieu College of Optical Sciences, University of Arizona [email protected] Meinel building R.626 Photodetectors Introduction Most important characteristics Photodetector types • Thermal photodetectors • Photoelectric effect • Semiconductor photodetectors Photodetectors p-n photodiode Response time p-i-n photodiode APD photodiode Noise Wiring Arrayed detector (Home Reading) Point-to-point WDM Transmission System - Building Blocks - transmitter receiver l l 1 terminal transmission line terminal 1 Tx point-to-point link section Rx l2 span l2 amplifier span l3 SMF or SMF or l3 NZDF NZDF EDFA EDFA EDFA l4 l4 DC DC l l 5 WDM mux 5 WDM demux l6 l6 dispersion dispersion ) amplifier - compensation compensation transmissionfiber transmissionfiber line) amplifier - (pre (in (booster) (booster) amplifier ln ln Raman Raman pump pump Laser sources Photodetectors Introduction Convert optical data into electrical data Laser beam characterization • Power measurement • Pulse energy measurement • Temporal waveform measurement • Beam profile Introduction Photodetector converts photon energy to a signal, mostly electric signal such as current (sort of a reverse LED) Photoelectric detector • Carrier generation by incident light • Carrier transport and/or multiplication by current gain mechanism • Interaction of current with external circuit Thermal detector • Conversion of photon to phonon (heat) • Propagation of phonon • Detection of phonon Important characteristics Wavelength coverage Sensitivity Bandwidth (response -
Cds Photo Resistors
TOKEN PGM CDS Photoresistors CDS Light-Dependent Photoresistors Light-Dependent Photoresistors for Sensor Applications Preview The cadmium sulfide (CdS) or light dependent resistor (LDR) whose resistance is inversly dependent on the amount of light falling on it, is known by many names including the photo resistor, photoresistor, photoconductor, photoconductive cell, or simply the photocell. A typical structure for a photoresistor uses an active semiconductor layer that is deposited on an insulating substrate. The semiconductor is normally lightly doped to enable it to have the required level of conductivity. Contacts are then placed either side of the exposed area. The photo-resistor, CdS, or LDR finds many uses as a low cost photo sensitive element and was used for many years in photographic light meters as well as in other applications such as smoke, flame and burglar detectors, card readers and lighting controls for street lamps. Providing design engineers with an economical CdS or LDR with high quality performance, Token Electronics now offers commercial grade PGM photoresistor. Designated the PGM Series, the photoresistors are available in 5mm, 12mm and 20mm sizes, the conformally epoxy or hermetical package offer high quality performance for applications that require quick response and good characteristic of spectrum. Token has been designing and manufacturing high performance light dependent resistors for decades. Our product offerings are extensive and our experience with custom photoresistor is equally extensive. Contact us with your specific needs. Features - Quick Response - Reliable Performance - Epoxy or hermetical package - Good Characteristic of Spectrum Applications - Photoswitch - Photoelectric Control - Auto Flash for Camera - Electronic Toys, Industrial Control TOKEN PGM CDS Photoresistors Terminology ● Light Resistance : Measured at 10 lux with standard light A Sensitive surface Electrodes (2854K-color temperature) and 2hr. -
Photoconductivity of Few-Layered P-Wse2 Phototransistors Via Multi-Terminal Measurements
Photoconductivity of few-layered p-WSe2 phototransistors via multi-terminal measurements Nihar R. Pradhan a,*, Carlos Garcia a,b, Joshua Holleman a,b, Daniel Rhodes a,b, Chason Parkera,c, Saikat Talapatra d, Mauricio Terrones e,f, Luis Balicas a,* and Stephen A. McGill a ,* aNational High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA bDepartment of Physics, Florida State University, Tallahassee, FL 32306, USA c Leon High School, Tallahassee, FL 32308, USA dDepartment of Physics, Southern Illinois University, Carbondale, IL 62901, USA eDepartment of Physics, Pennsylvania State University, PA 16802, USA fCenter for 2-Dimensional and Layered Materials, Pennsylvania State University, PA 16802, USA Abstract: Recently, two-dimensional materials and in particular transition metal dichalcogenides (TMDs) were extensively studied because of their strong light-matter interaction and the remarkable optoelectronic response of their field-effect transistors (FETs). Here, we report a photoconductivity study from FETs built from few-layers of p-WSe2 measured in a multi-terminal configuration under illumination by a 532 nm laser source. The photogenerated current was measured as a function of the incident optical power, of the drain-to-source bias and of the gate voltage. We observe a considerably larger photoconductivity when the phototransistors were measured via a four-terminal configuration when compared to a two-terminal one. For an incident laser power of 248 nW, we extract 18 A/W and ~4000% for the two-terminal responsivity (R) and the concomitant external quantum efficiency (EQE) respectively, when a bias voltage Vds = 1 V and a gate voltage Vbg = 10 V are applied to the sample. -
An Investigation on the Printing of Metal and Polymer Powders Using Electrophotographic Solid Freeform Fabrication
AN INVESTIGATION ON THE PRINTING OF METAL AND POLYMER POWDERS USING ELECTROPHOTOGRAPHIC SOLID FREEFORM FABRICATION By AJAY KUMAR DAS A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004 Copyright 2004 by Ajay Kumar Das Dedicated to my mother. ACKNOWLEDGMENTS I extend my sincere gratitude to my advisor and chairman of the thesis committee, Dr. Ashok V. Kumar for his guidance and support during the research work which made this thesis possible. I would also like to thank the thesis committee members Dr. John K. Schueller and Dr. Nagaraj Arakere for their patience in reviewing the thesis and for their valuable advice during the research work. I thank the Design and Rapid Prototyping Laboratory co-workers for being helpful, supportive and making the research a pleasurable experience. Last but not least, I would like to thank my parents for their love and encouragement during my studies abroad. iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS ................................................................................................. iv LIST OF TABLES............................................................................................................. ix LIST OF FIGURES ........................................................................................................... xi ABSTRACT.......................................................................................................................xv CHAPTER -
Laser Printer - Wikipedia, the Free Encyclopedia
Laser printer - Wikipedia, the free encyclopedia http://en. rvi kipedia.org/r,vi ki/Laser_pri nter Laser printer From Wikipedia, the free encyclopedia A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. As with digital photocopiers and multifunction printers (MFPs), Iaser printers employ a xerographic printing process but differ from analog photocopiers in that the image is produced by the direct scanning of a laser beam across the printer's photoreceptor. Overview A laser beam projects an image of the page to be printed onto an electrically charged rotating drum coated with selenium. Photoconductivity removes charge from the areas exposed to light. Dry ink (toner) particles are then electrostatically picked up by the drum's charged areas. The drum then prints the image onto paper by direct contact and heat, which fuses the ink to the paper. HP I-aserJet 4200 series printer Laser printers have many significant advantages over other types of printers. Unlike impact printers, laser printer speed can vary widely, and depends on many factors, including the graphic intensity of the job being processed. The fastest models can print over 200 monochrome pages per minute (12,000 pages per hour). The fastest color laser printers can print over 100 pages per minute (6000 pages per hour). Very high-speed laser printers are used for mass mailings of personalized documents, such as credit card or utility bills, and are competing with lithography in some commercial applications. The cost of this technology depends on a combination of factors, including the cost of paper, toner, and infrequent HP LaserJet printer drum replacement, as well as the replacement of other 1200 consumables such as the fuser assembly and transfer assembly. -
High-Temperature Ultraviolet Photodetectors: a Review
High-temperature Ultraviolet Photodetectors: A Review Ruth A. Miller,1 Hongyun So,2 Thomas A. Heuser,3 and Debbie G. Senesky1, a) 1Department of Aeronautics and Astronautics Stanford University, Stanford, CA 94305, USA 2Department of Mechanical Engineering Hanyang University, Seoul 04763, Korea 3Department of Materials Science and Engineering Stanford University, Stanford, CA 94305, USA Abstract Wide bandgap semiconductors have become the most attractive materials in optoelectronics in the last decade. Their wide bandgap and intrinsic properties have advanced the development of reliable photodetectors to selectively detect short wavelengths (i.e., ultraviolet, UV) in high temperature regions (up to 300°C). The main driver for the development of high-temperature UV detection instrumentation is in-situ monitoring of hostile environments and processes found within industrial, automotive, aerospace, and energy production systems that emit UV signatures. In this review, a summary of the optical performance (in terms of photocurrent-to-dark current ratio, responsivity, quantum efficiency, and response time) and uncooled, high-temperature characterization of III-nitride, SiC, and other wide bandgap semiconductor UV photodetectors is presented. a) Author to whom correspondence should be addressed. E-mail: [email protected] 1 I. INTRODUCTION On the electromagnetic spectrum, the ultraviolet (UV) region spans wavelengths from 400 nm to 10 nm (corresponding to photon energies from 3 eV to 124 eV) and is typically divided into three spectral bands: UV-A (400–320 nm), UV-B (320–280 nm), and UV-C (280– 10 nm). The Sun is the most significant natural UV source. The approximate solar radiation spectrum just outside Earth’s atmosphere, calculated as black body radiation at 5800 K using Plank’s law, is shown in Fig. -
Photosensitive Camera Tubes and Devices Handbook
11.2 PHOTOSENSITIVE CAMERA TUBES AND DEVICES 11.1 PHOTOSENSITIVITY / 11.2 11.1.1 Photoemitters / 11.2 11.1.2 Photoconductors / 11.5 11.2 PHOTOELECTRIC-INDUCED TELEVISION SIGNAL GENERATION / 11.5 11.2.1 Photoemission-Induced Charge Images / 11.5 11.2.2 Secondary-Emission-Induced Charge Images / 11.6 11.2.3 Electron-Bombardment-Induced Conductivity / 11.8 11.2.4 Photoconductive-Generated Charge Images / 11.9 11.2.5 Generation of Video Signals by Scanning / 11.11 11.2.6 Low-Velocity Scanning / 11.11 11.2.7 Return-Beam Signal Generation / 11.13 11.2.8 High-Velecity Scanning / 11.14 11.3 EVOLUTION AND DEVELOPMENT OF TELEVISION CAMERA TUBES / 11.14 11.3.1 Nonstorage Tubes / 11.14 11.3.2 Storage Tubes / 11.15 11.4 VIDICON-TYPE CAMERA TUBES / 11.26 11.4.1 Antimony Trisulfide Photoconductor / 11.26 11.4.2 Lead Oxide Photoconductor / 11.28 11.4.3 Selenium Photoconductor / 11.30 11.4.4 Silicon-Diode Photoconductive Target / 11.31 11.4.5 Cadmium Selenide Photoconductor / 11.32 11.4.6 Zinc Selenide Photoconductor / 11.32 11.5 INTERFACE WITH THE CAMERA / 11.33 11.5.1 Optical Input / 11.34 11.5.2 Operating Voltages / 11.34 11.5.3 Dynamic Focusing / 11.36 11.5.4 Beam Blanking / 11.36 11.5.5 Beam Trajectory Control / 11.38 11.5.6 Video Output / 11.40 11.5.7 Deflecting Coils and Circuits / 11.42 11.5.8 Magnetic Shielding / 11.42 11.5.9 Anti-Comet-Tail Tube / 11.42 11.6 CAMERA TUBE PERFORMANCE CHARACTERISTICS / 11.43 11.6.1 Sensitivity and Output / 11.44 11.6.2 Resolution / 11.45 11.6.3 Lag / 11.49 11.6.4 Lag-Reduction Techniques / 11.50 11.7 SINGLE-TUBE COLOR CAMERA SYSTEMS / 11.54 11.7.1 Single-Output-Signal Tubes / 11.55 11.7.2 Multiple-Output-Signal Tubes / 11.58 11.8 SOLID-STATE IMAGER DEVELOPMENT / 11.60 11.8.1 Early Imager Devices / 11.60 11.8.2 Improvements in Signal-to-Noise Ratio / 11.60 11.8.3 CCD Structures / 11.61 11.8.4 New Developments / 11.63 REFERENCES / 11.64 PHOTOSENSITIVITY 11.3 11.1 PHOTOSENSITIVITY A photosensitive camera tube is the light-sensitive device utilized in a television camera to develop the video signal. -
Peering Into the Electric Eye: What Is a Photoresistor?
Peering Into the Electric Eye: What is a Photoresistor? Subject Area(s) Physical Science, Science and Technology Associated Unit None Associated Lesson None Activity Title Peering into the electric eye: What is a photoresistor? Header Insert image 1 here, right justified to wrap Image 1 ADA Description: Students assembling a photoresistor circuit Caption: Students integrating a photoresistor circuit with an autonomous robot Image file name: ldr_image1.jpg Source/Rights: Copyright 2009 Damion Irving. Used with permission. Grade Level 8 (9-12) Activity Dependency None Time Required 90 minutes Group Size 3 – 5 Expendable Cost per Group $15 Insert Figure 1 here, centered Figure 1 ADA Description: Principle of operation of a photoresistor Caption: Working of a photoresistor presented according to the anatomy of a sensor Image file name: ldr_figure1.gif Source/Rights: Copyright 2009 Damion Irving. Used with permission. Summary This activity aims to introduce to students a photoresistor, which is often used in a light dependent voltage divider circuit. A photoresistor is part of a larger family of devices or sensors known as photodetectors. A photodetector’s resistance to electrical current changes when it is exposed to light. Photodetectors are commonly used as light sensitive switches; for examples common streetlights that turn on at dusk employ photoresistor circuits. As depicted in Figure 1, the basic anatomy of a sensor can be used to explain the operation of a photoresistor. The following mnemonic is used: Sensors = Stimulus + Transducer + Signal (STS). That is, a sensor is a device that detects an external stimulus, and it changes that stimulus to a detectable signal, by means of a transducer. -
Cdse/Zns Quantum Dot Encapsulated Mos2 Phototransistor for Enhanced
www.nature.com/scientificreports OPEN CdSe/ZnS quantum dot encapsulated MoS2 phototransistor for enhanced radiation hardness Received: 7 June 2018 Jinwu Park1, Geonwook Yoo2 & Junseok Heo1 Accepted: 17 December 2018 Notable progress achieved in studying MoS based phototransistors reveals the great potential to Published: xx xx xxxx 2 be applicable in various feld of photodetectors, and to further expand it, a durability study of MoS2 phototransistors in harsh environments is highly required. Here, we investigate efects of gamma rays on the characteristics of MoS2 phototransistors and improve its radiation hardness by incorporating CdSe/ZnS quantum dots as an encapsulation layer. A 73.83% decrease in the photoresponsivity was observed after gamma ray irradiation of 400 Gy, and using a CYTOP and CdSe/ZnS quantum dot layer, the photoresponsivity was successfully retained at 75.16% on average after the gamma ray irradiation. Our results indicate that the CdSe/ZnS quantum dots having a high atomic number can be an efective encapsulation method to improve radiation hardness and thus to maintain the performance of the MoS2 phototransistor. Two-dimensional materials such as transition metal dichalcogenides (TMD) have received considerable attention as a promising channel material for nanoelectronics devices1–6. Among a variety of TMD materials, molybdenum disulfde (MoS2) is the best known and is studied extensively. MoS2-based thin-flm transistors have interest- ing electrical characteristics, such as high ON/OFF ratio (~108) and high electron mobility (~200 cm2∙Vs−1)1. In addition, MoS2 is appropriate as an absorption layer of optoelectronic devices owing to its bandgap of 1.2–1.8 eV 7 depending on its number of layers (bulk MoS2 has an indirect bandgap of 1.2 eV and single-layer MoS2 has a direct bandgap of 1.8 eV8), fast photo-switching (within 110 μs9), and absorption coefcient (α = 1–1.5 × 106 cm−1 10 6 −1 11 for single-layer MoS2 and 0.1–0.6 × 10 cm for bulk MoS2 in the wavelength of 500–1200 nm). -
Poly(N-Vinylcarbazole) (PVK) Photoconductivity Enhancement Induced by Doping with Cds Nanocrystals Through Chemical Hybridization
J. Phys. Chem. B 2000, 104, 11853-11858 11853 Poly(N-vinylcarbazole) (PVK) Photoconductivity Enhancement Induced by Doping with CdS Nanocrystals through Chemical Hybridization Suhua Wang,† Shihe Yang,*,† Chunlei Yang,‡ Zongquan Li,‡ Jiannong Wang,‡ and Weikun Ge‡ Department of Chemistry, The Hong Kong UniVersity of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, and Department of Physics, The Hong Kong UniVersity of Science and Technology, Clear Water Bay, Kowloon, Hong Kong ReceiVed: February 9, 2000; In Final Form: June 7, 2000 We have functionalized poly(N-vinyl carbazole) (PVK) by controlled sulfonation. CdS nanocystals of 3-20 nm across were synthesized in the sulfonated PVK matrix with the CdS molar fraction of ∼1-18%. The CdS nanoparticle size increased with the molar fraction of CdS. At high CdS molar fractions, the CdS nanocrystals exist in both cubic and hexagonal phases. Photoluminescence efficiency of PVK decreases when the molar fraction of CdS increases due to quenching through interfacial charge transfer. Photoluminescence attributable to the CdS nanocrystals can be observed only at low molar fractions of CdS. Significant enhancement in photoconductivity induced by the chemical doping of CdS in PVK has also been demonstrated. Introduction formation of the CdS-PVK nanocomposite. The maximum molar fraction of CdS in the nanocomposite was ∼18% (∼5% Nanocomposites consisting of inorganic nanoparticles and v/v) based on the sulfonation degree of PVK, as determined by organic polymers often exhibit a host of mechanical, electrical, both X-ray photoelectron spectroscopy (XPS) and secondary optical and magnetic properties, which are far superior compared 7 1-4 ion mass spectrometry (SIMS). -
Optoelectronic Devices Are Electrical-To- Optical Or Optical-To-Electrical Transducers
Pablo Rocamora Montoro Introduction Is the study and application of electronic devices that source, control and detect light. It combine electronics and optics. Optoelectronic devices are electrical-to- optical or optical-to-electrical transducers. Its operation is based on the wave theory and quantum mechanics . We can distinguish 3 categories: . Light Emitters. Light Receivers. Optocouplers. LIGHT EMITTERS Among semiconductor devices, those capable of emitting light belong to the category of the diodes. Led (Ligth-emitting diode) Laser diode. LEDs Is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence. LEDs Many advantages over incandescent light sources and fluorescent: . Low power consumption. Longer life. Small size. Vibration resistance. Do not contain mercury. Low emission of heat. LEDs APPLICATIONS 3 main types of applications for LEDs: . Indicators and signs. Lighting or illumination. Measuring/interacting in processes involving no human vision. LASER DIODE Light Amplification by Stimulated Emission of Radiation is an electrically pumped semiconductor laser in which the active laser medium is formed by a p-n junction of a semiconductor diode similar to that found in a LED. LASER DIODE Advantages over LEDs: . Light emission in only one direction. Laser light emission is monochromatic LASER DIODE APPLICATIONS Data communications fiber optics. Optical interconnections between integrated circuits. Laser printers. Scanners and digitizers. Sensors. Dental laser treatment. Body hair removal. Laser display Odontology LIGHT RECEPTORS Are those components that vary an electrical parameter depending on the light.