Band-edge electroluminescence of crystalline silicon heterostructure solar cells

Semiconductor Manufacturing Technology半导体制造技术Instructor’s ManualMichael QuirkJulian SerdaCopyright Prentice HallTable of Contents目录OverviewI. Chapter1. Semiconductor industry overview2. Semiconductor materials3. Device technologies—IC families4. Silicon and wafer preparation5. Chemicals in the industry6. Contamination control7. Process metrology8. Process gas controls9. IC fabrication overview10. Oxidation11. Deposition12. Metallization13. Photoresist14. Exposure15. Develop16. Etch17. Ion implant18. Polish19. Test20. Assembly and packagingII. Answers to End-of-Chapter Review QuestionsIII. Test Bank (supplied on diskette)IV. Chapter illustrations, tables, bulleted lists and major topics (supplied on CD-ROM)Notes to Instructors:1)The chapter overview provides a concise summary of the main topics in each chapter.2)The correct answer for each test bank question is highlighted in bold. Test bankquestions are based on the end-of-chapter questions. If a student studies the end-of-chapter questions (which are linked to the italicized words in each chapter), then they will be successful on the test bank questions.2Chapter 1Introduction to the Semiconductor Industry Die:管芯 defective:有缺陷的Development of an Industry•The roots of the electronic industry are based on the vacuum tube and early use of silicon for signal transmission prior to World War II. The first electronic computer, the ENIAC, wasdeveloped at the University of Pennsylvania during World War II.•William Shockley, John Bardeen and Walter Brattain invented the solid-state transistor at Bell Telephone Laboratories on December 16, 1947. The semiconductor industry grew rapidly in the 1950s to commercialize the new transistor technology, with many early pioneers working inSilicon Valley in Northern California.Circuit Integration•The first integrated circuit, or IC, was independently co-invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor in 1959. An IC integrates multiple electronic components on one substrate of silicon.•Circuit integration eras are: small scale integration (SSI) with 2 - 50 components, medium scale integration (MSI) with 50 – 5k components, large scale integration (LSI) with 5k to 100kcomponents, very large scale integration (VLSI) with 100k to 1M components, and ultra large scale integration (ULSI) with > 1M components.1IC Fabrication•Chips (or die) are fabricated on a thin slice of silicon, known as a wafer (or substrate). Wafers are fabricated in a facility known as a wafer fab, or simply fab.•The five stages of IC fabrication are:Wafer preparation: silicon is purified and prepared into wafers.Wafer fabrication: microchips are fabricated in a wafer fab by either a merchant chip supplier, captive chip producer, fabless company or foundry.Wafer test: Each individual die is probed and electrically tested to sort for good or bad chips.Assembly and packaging: Each individual die is assembled into its electronic package.Final test: Each packaged IC undergoes final electrical test.•Key semiconductor trends are:Increase in chip performance through reduced critical dimensions (CD), more components per chip (Moore’s law, which predicts the doubling of components every 18-24 months) andreduced power consumption.Increase in chip reliability during usage.Reduction in chip price, with an estimated price reduction of 100 million times for the 50 years prior to 1996.The Electronic Era•The 1950s saw the development of many different types of transistor technology, and lead to the development of the silicon age.•The 1960s were an era of process development to begin the integration of ICs, with many new chip-manufacturing companies.•The 1970s were the era of medium-scale integration and saw increased competition in the industry, the development of the microprocessor and the development of equipment technology. •The 1980s introduced automation into the wafer fab and improvements in manufacturing efficiency and product quality.•The 1990s were the ULSI integration era with the volume production of a wide range of ICs with sub-micron geometries.Career paths•There are a wide range of career paths in semiconductor manufacturing, including technician, engineer and management.2Chapter 2 Characteristics of Semiconductor MaterialsAtomic Structure•The atomic model has three types of particles: neutral neutrons（不带电的中子）, positively charged protons（带正电的质子）in the nucleus and negatively charged electrons（带负电的核外电子） that orbit the nucleus. Outermost electrons are in the valence shell, and influence the chemical and physical properties of the atom. Ions form when an atom gains or loses one or more electrons.The Periodic Table•The periodic table lists all known elements. The group number of the periodic table represents the number of valence shell electrons of the element. We are primarily concerned with group numbers IA through VIIIA.•Ionic bonds are formed when valence shell electrons are transferred from the atoms of one element to another. Unstable atoms (e.g., group VIIIA atoms because they lack one electron) easily form ionic bonds.•Covalent bonds have atoms of different elements that share valence shell electrons.3Classifying Materials•There are three difference classes of materials:ConductorsInsulatorsSemiconductors•Conductor materials have low resistance to current flow, such as copper. Insulators have high resistance to current flow. Capacitance is the storage of electrical charge on two conductive plates separated by a dielectric material. The quality of the insulation material between the plates is the dielectric constant. Semiconductor materials can function as either a conductor or insulator.Silicon•Silicon is an elemental semiconductor material because of four valence shell electrons. It occurs in nature as silica and is refined and purified to make wafers.•Pure silicon is intrinsic silicon. The silicon atoms bond together in covalent bonds, which defines many of silicon’s properties. Silicon atoms bond together in set, repeatable patterns, referred to asa crystal.•Germanium was the first semiconductor material used to make chips, but it was soon replaced by silicon. The reasons for this change are:Abundance of siliconHigher melting temperature for wider processing rangeWide temperature range during semiconductor usageNatural growth of silicon dioxide•Silicon dioxide (SiO2) is a high quality, stable electrical insulator material that also serves as a good chemical barrier to protect silicon from external contaminants. The ability to grow stable, thin SiO2 is fundamental to the fabrication of Metal-Oxide-Semiconductor (MOS) devices. •Doping increases silicon conductivity by adding small amounts of other elements. Common dopant elements are from trivalent, p-type Group IIIA (boron) and pentavalent, n-type Group VA (phosphorus, arsenic and antimony).•It is the junction between the n-type and p-type doped regions (referred to as a pn junction) that permit silicon to function as a semiconductor.4Alternative Semiconductor Materials•The alternative semiconductor materials are primarily the compound semiconductors. They are formed from Group IIIA and Group VA (referred to as III-V compounds). An example is gallium arsenide (GaAs).•Some alternative semiconductors come from Group IIA and VIA, referred to as II-VI compounds. •GaAs is the most common III-V compound semiconductor material. GaAs ICs have greater electron mobility, and therefore are faster than ICs made with silicon. GaAs ICs also have higher radiation hardness than silicon, which is better for space and military applications. The primary disadvantage of GaAs is the lack of a natural oxide.5Chapter 3Device TechnologiesCircuit Types•There are two basic types of circuits: analog and digital. Analog circuits have electrical data that varies continuously over a range of voltage, current and power values. Digital circuits have operating signals that vary about two distinct voltage levels – a high and a low.Passive Component Structures•Passive components such as resistors and capacitors conduct electrical current regardless of how the component is connected. IC resistors are a passive component. They can have unwanted resistance known as parasitic resistance. IC capacitor structures can also have unintentional capacitanceActive Component Structures•Active components, such as diodes and transistors can be used to control the direction of current flow. PN junction diodes are formed when there is a region of n-type semiconductor adjacent to a region of p-type semiconductor. A difference in charge at the pn junction creates a depletion region that results in a barrier voltage that must be overcome before a diode can be operated. A bias voltage can be configured to have a reverse bias, with little or no conduction through the diode, or with a forward bias, which permits current flow.•The bipolar junction transistor (BJT) has three electrodes and two pn junctions. A BJT is configured as an npn or pnp transistor and biased for conduction mode. It is a current-amplifying device.6• A schottky diode is formed when metal is brought in contact with a lightly doped n-type semiconductor material. This diode is used in faster and more power efficient BJT circuits.•The field-effect transistor (FET), a voltage-amplifying device, is more compact and power efficient than BJT devices. A thin gate oxide located between the other two electrodes of the transistor insulates the gate on the MOSFET. There are two categories of MOSFETs, nMOS (n-channel) and pMOS (p-channel), each which is defined by its majority current carriers. There is a biasing scheme for operating each type of MOSFET in conduction mode.•For many years, nMOS transistors have been the choice of most IC manufacturers. CMOS, with both nMOS and pMOS transistors in the same IC, has been the most popular device technology since the early 1980s.•BiCMOS technology makes use of the best features of both CMOS and bipolar technology in the same IC device.•Another way to categorize FETs is in terms of enhancement mode and depletion mode. The major different is in the way the channels are doped: enhancement-mode channels are doped opposite in polarity to the source and drain regions, whereas depletion mode channels are doped the same as their respective source and drain regions.Latchup in CMOS Devices•Parasitic transistors can create a latchup condition(???????) in CMOS ICs that causes transistors to unintentionally（无心的） turn on. To control latchup, an epitaxial layer is grown on the wafer surface and an isolation barrier（隔离阻障）is placed between the transistors. An isolation layer can also be buried deep below the transistors.Integrated Circuit Productsz There are a wide range of semiconductor ICs found in electrical and electronic products. This includes the linear IC family, which operates primarily with anal3og circuit applications, and the digital IC family, which includes devices that operate with binary bits of data signals.7Chapter 4Silicon and Wafer Preparation8z Semiconductor-Grade Silicon•The highly refined silicon used for wafer fabrication is termed semiconductor-grade silicon (SGS), and sometimes referred to as electronic-grade silicon. The ultra-high purity of semiconductor-grade silicon is obtained from a multi-step process referred to as the Siemens process.Crystal Structure• A crystal is a solid material with an ordered, 3-dimensional pattern over a long range. This is different from an amorphous material that lacks a repetitive structure.•The unit cell is the most fundamental entity for the long-range order found in crystals. The silicon unit cell is a face-centered cubic diamond structure. Unit cells can be organized in a non-regular arrangement, known as a polycrystal. A monocrystal are neatly arranged unit cells.Crystal Orientation•The orientation of unit cells in a crystal is described by a set of numbers known as Miller indices.The most common crystal planes on a wafer are (100), (110), and (111). Wafers with a (100) crystal plane orientation are most common for MOS devices, whereas (111) is most common for bipolar devices.Monocrystal Silicon Growth•Silicon monocrystal ingots are grown with the Czochralski (CZ) method to achieve the correct crystal orientation and doping. A CZ crystal puller is used to grow the silicon ingots. Chunks of silicon are heated in a crucible in the furnace of the puller, while a perfect silicon crystal seed is used to start the new crystal structure.• A pull process serves to precisely replicate the seed structure. The main parameters during the ingot growth are pull rate and crystal rotation. More homogeneous crystals are achieved with a magnetic field around the silicon melt, known as magnetic CZ.•Dopant material is added to the melt to dope the silicon ingot to the desired electrical resistivity.Impurities are controlled during ingot growth. A float-zone crystal growth method is used toachieve high-purity silicon with lower oxygen content.•Large-diameter ingots are grown today, with a transition underway to produce 300-mm ingot diameters. There are cost benefits for larger diameter wafers, including more die produced on a single wafer.Crystal Defects in Silicon•Crystal defects are interruptions in the repetitive nature of the unit cell. Defect density is the number of defects per square centimeter of wafer surface.•Three general types of crystal defects are: 1) point defects, 2) dislocations, and 3) gross defects.Point defects are vacancies (or voids), interstitial (an atom located in a void) and Frenkel defects, where an atom leaves its lattice site and positions itself in a void. A form of dislocation is astacking fault, which is due to layer stacking errors. Oxygen-induced stacking faults are induced following thermal oxidation. Gross defects are related to the crystal structure (often occurring during crystal growth).Wafer Preparation•The cylindrical, single-crystal ingot undergoes a series of process steps to create wafers, including machining operations, chemical operations, surface polishing and quality checks.•The first wafer preparation steps are the shaping operations: end removal, diameter grinding, and wafer flat or notch. Once these are complete, the ingot undergoes wafer slicing, followed by wafer lapping to remove mechanical damage and an edge contour. Wafer etching is done to chemically remove damage and contamination, followed by polishing. The final steps are cleaning, wafer evaluation and packaging.Quality Measures•Wafer suppliers must produce wafers to stringent quality requirements, including: Physical dimensions: actual dimensions of the wafer (e.g., thickness, etc.).Flatness: linear thickness variation across the wafer.Microroughness: peaks and valleys found on the wafer surface.Oxygen content: excessive oxygen can affect mechanical and electrical properties.Crystal defects: must be minimized for optimum wafer quality.Particles: controlled to minimize yield loss during wafer fabrication.Bulk resistivity(电阻系数): uniform resistivity from doping during crystal growth is critical. Epitaxial Layer•An epitaxial layer (or epi layer) is grown on the wafer surface to achieve the same single crystal structure of the wafer with control over doping type of the epi layer. Epitaxy minimizes latch-up problems as device geometries continue to shrink.Chapter 5Chemicals in Semiconductor FabricationEquipment Service Chase Production BayChemical Supply Room Chemical Distribution Center Holding tank Chemical drumsProcess equipmentControl unit Pump Filter Raised and perforated floorElectronic control cablesSupply air ductDual-wall piping for leak confinement PumpFilterChemical control and leak detection Valve boxes for leak containment Exhaust air ductStates of Matter• Matter in the universe exists in 3 basic states (宇宙万物存在着三种基本形态): solid, liquid andgas. A fourth state is plasma.Properties of Materials• Material properties are the physical and chemical characteristics that describe its unique identity.• Different properties for chemicals in semiconductor manufacturing are: temperature, pressure andvacuum, condensation, vapor pressure, sublimation and deposition, density, surface tension, thermal expansion and stress.Temperature is a measure of how hot or cold a substance is relative to another substance. Pressure is the force exerted per unit area. Vacuum is the removal of gas molecules.Condensation is the process of changing a gas into a liquid. Vaporization is changing a liquidinto a gas.Vapor pressure is the pressure exerted by a vapor in a closed container at equilibrium.Sublimation is the process of changing a solid directly into a gas. Deposition is changing a gas into a solid.Density is the mass of a substance divided by its volume.Surface tension of a liquid is the energy required to increase the surface area of contact.Thermal expansion is the increase in an object’s dimension due to heating.Stress occurs when an object is exposed to a force.Process Chemicals•Semiconductor manufacturing requires extensive chemicals.• A chemical solution is a chemical mixture. The solvent is the component of the solution present in larger amount. The dissolved substances are the solutes.•Acids are solutions that contain hydrogen and dissociate in water to yield hydronium ions. A base is a substance that contains the OH chemical group and dissociates in water to yield the hydroxide ion, OH-.•The pH scale is used to assess the strength of a solution as an acid or base. The pH scale varies from 0 to 14, with 7 being the neutral point. Acids have pH below 7 and bases have pH values above 7.• A solvent is a substance capable of dissolving another substance to form a solution.• A bulk chemical distribution (BCD) system is often used to deliver liquid chemicals to the process tools. Some chemicals are not suitable for BCD and instead use point-of-use (POU) delivery, which means they are stored and used at the process station.•Gases are generally categorized as bulk gases or specialty gases. Bulk gases are the relatively simple gases to manufacture and are traditionally oxygen, nitrogen, hydrogen, helium and argon.The specialty gases, or process gases, are other important gases used in a wafer fab, and usually supplied in low volume.•Specialty gases are usually transported to the fab in metal cylinders.•The local gas distribution system requires a gas purge to flush out undesirable residual gas. Gas delivery systems have special piping and connections systems. A gas stick controls the incoming gas at the process tool.•Specialty gases may be classified as hydrides, fluorinated compounds or acid gases.Chapter 6Contamination Control in Wafer FabsIntroduction•Modern semiconductor manufacturing is performed in a cleanroom, isolated from the outside environment and contaminants.Types of contamination•Cleanroom contamination has five categories: particles, metallic impurities, organic contamination, native oxides and electrostatic discharge. Killer defects are those causes of failure where the chip fails during electrical test.Particles: objects that adhere to a wafer surface and cause yield loss. A particle is a killer defect if it is greater than one-half the minimum device feature size.Metallic impurities: the alkali metals found in common chemicals. Metallic ions are highly mobile and referred to as mobile ionic contaminants (MICs).Organic contamination: contains carbon, such as lubricants and bacteria.Native oxides: thin layer of oxide growth on the wafer surface due to exposure to air.Electrostatic discharge (ESD): uncontrolled transfer of static charge that can damage the microchip.Sources and Control of Contamination•The sources of contamination in a wafer fab are: air, humans, facility, water, process chemicals, process gases and production equipment.Air: class number designates the air quality inside a cleanroom by defining the particle size and density.Humans: a human is a particle generator. Humans wear a cleanroom garment and follow cleanroom protocol to minimize contamination.Facility: the layout is generally done as a ballroom (open space) or bay and chase design.Laminar airflow with air filtering is used to minimize particles. Electrostatic discharge iscontrolled by static-dissipative materials, grounding and air ionization.Ultrapure deiniozed (DI) water: Unacceptable contaminants are removed from DI water through filtration to maintain a resistivity of 18 megohm-cm. The zeta potential represents a charge on fine particles in water, which are trapped by a special filter. UV lamps are used for bacterial sterilization.Process chemicals: filtered to be free of contamination, either by particle filtration, microfiltration (membrane filter), ultrafiltration and reverse osmosis (or hyperfiltration).Process gases: filtered to achieve ultraclean gas.Production equipment: a significant source of particles in a fab.Workstation design: a common layout is bulkhead equipment, where the major equipment is located behind the production bay in the service chase. Wafer handling is done with robotic wafer handlers. A minienvironment is a localized environment where wafers are transferred on a pod and isolated from contamination.Wafer Wet Cleaning•The predominant wafer surface cleaning process is with wet chemistry. The industry standard wet-clean process is the RCA clean, consisting of standard clean 1 (SC-1) and standard clean 2 (SC-2).•SC-1 is a mixture of ammonium hydroxide, hydrogen peroxide and DI water and capable of removing particles and organic materials. For particles, removal is primarily through oxidation of the particle or electric repulsion.•SC-2 is a mixture of hydrochloric acid, hydrogen peroxide and DI water and used to remove metals from the wafer surface.•RCA clean has been modified with diluted cleaning chemistries. The piranha cleaning mixture combines sulfuric acid and hydrogen peroxide to remove organic and metallic impurities. Many cleaning steps include an HF last step to remove native oxide.•Megasonics(兆声清洗) is widely used for wet cleaning. It has ultrasonic energy with frequencies near 1 MHz. Spray cleaning will spray wet-cleaning chemicals onto the wafer. Scrubbing is an effective method for removing particles from the wafer surface.•Wafer rinse is done with overflow rinse, dump rinse and spray rinse. Wafer drying is done with spin dryer or IPA(异丙醇) vapor dry (isopropyl alcohol).•Some alternatives to RCA clean are dry cleaning, such as with plasma-based cleaning, ozone and cryogenic aerosol cleaning.Chapter 7Metrology and Defect InspectionIC Metrology•In a wafer fab, metrology refers to the techniques and procedures for determining physical and electrical properties of the wafer.•In-process data has traditionally been collected on monitor wafers. Measurement equipment is either stand-alone or integrated.•Yield is the percent of good parts produced out of the total group of parts started. It is an indicator of the health of the fabrication process.Quality Measures•Semiconductor quality measures define the requirements for specific aspects of wafer fabrication to ensure acceptable device performance.•Film thickness is generally divided into the measurement of opaque film or transparent film. Sheet resistance measured with a four-point probe is a common method of measuring opaque films (e.g., metal film). A contour map shows sheet resistance deviations across the wafer surface.•Ellipsometry is a nondestructive, noncontact measurement technique for transparent films. It works based on linearly polarized light that reflects off the sample and is elliptically polarized.•Reflectometry is used to measure a film thickness based on how light reflects off the top and bottom surface of the film layer. X-ray and photoacoustic technology are also used to measure film thickness.•Film stress is measured by analyzing changes in the radius of curvature of the wafer. Variations in the refractive index are used to highlight contamination in the film.•Dopant concentration is traditionally measured with a four-point probe. The latest technology is the thermal-wave system, which measures the lattice damage in the implanted wafer after ion implantation. Another method for measuring dopant concentration is spreading resistance probe. •Brightfield detection is the traditional light source for microscope equipment. An optical microscope uses light reflection to detect surface defects. Darkfield detection examines light scattered off defects on the wafer surface. Light scattering uses darkfield detection to detectsurface particles by illuminating the surface with laser light and then using optical imaging.•Critical dimensions (CDs) are measured to achieve precise control over feature size dimensions.The scanning electron microscope is often used to measure CDs.•Conformal step coverage is measured with a surface profiler that has a stylus tip.•Overlay registration measures the ability to accurately print photoresist patterns over a previously etched pattern.•Capacitance-voltage (C-V) test is used to verify acceptable charge conditions and cleanliness at the gate structure in a MOS device.Analytical Equipment•The secondary-ion mass spectrometry (SIMS) is a method of eroding a wafer surface with accelerated ions in a magnetic field to analyze the surface material composition.•The atomic force microscope (AFM) is a surface profiler that scans a small, counterbalanced tip probe over the wafer to create a 3-D surface map.•Auger electron spectroscopy (AES) measures composition on the wafer surface by measuring the energy of the auger electrons. It identifies elements to a depth of about 2 nm. Another instrument used to identify surface chemical species is X-ray photoelectron spectroscopy (XPS).•Transmission electron microscopy (TEM) uses a beam of electrons that is transmitted through a thin slice of the wafer. It is capable of quantifying very small features on a wafer, such as silicon crystal point defects.•Energy-dispersive spectrometer (EDX) is a widely used X-ray detection method for identifying elements. It is often used in conjunction with the SEM.• A focused ion beam (FIB) system is a destructive technique that focuses a beam of ions on the wafer to carve a thin cross section from any wafer area. This permits analysis of the wafermaterial.Chapter 8Gas Control in Process ChambersEtch process chambers••The process chamber is a controlled vacuum environment where intended chemical reactions take place under controlled conditions. Process chambers are often configured as a cluster tool. Vacuum•Vacuum ranges are low (rough) vacuum, medium vacuum, high vacuum and ultrahigh vacuum (UHV). When pressure is lowered in a vacuum, the mean free path(平均自由行程) increases, which is important for how gases flow through the system and for creating a plasma.Vacuum Pumps•Roughing pumps are used to achieve a low to medium vacuum and to exhaust a high vacuum pump. High vacuum pumps achieve a high to ultrahigh vacuum.•Roughing pumps are dry mechanical pumps or a blower pump (also referred to as a booster). Two common high vacuum pumps are a turbomolecular (turbo) pump and cryopump. The turbo pump is a reliable, clean pump that works on the principle of mechanical compression. The cryopump isa capture pump that removes gases from the process chamber by freezing them.。

——电材专业英语课文翻译Semiconductor Materials• 1.1 Energy Bands and Carrier Concentration• 1.1.1 Semiconductor Materials•Solid-state materials can be grouped into three classes—insulators(绝缘体）, semiconductors, and conductors. Figure 1-1 shows the electrical conductivities δ(and the corresponding resistivities ρ≡1/δ)associated with(相关）some important materials in each of three classes. Insulators such as fused（熔融）quartz and glass have very low conductivities, in the order of 1E-18 to 1E-8 S/cm;固态材料可分为三种：绝缘体、半导体和导体。

图1－1 给出了在三种材料中一些重要材料相关的电阻值（相应电导率ρ≡1/δ)。

绝缘体如熔融石英和玻璃具有很低电导率，在10-18 到10-8 S/cm;and conductors such as aluminum and silver have high conductivities, typically from 104 to 106 S/cm. Semiconductors have conductivities between those of insulators and those of conductors. The conductivity of a semiconductor is generally sensitive to temperature, illumination（照射）, magnetic field, and minute amount of impurity atoms. This sensitivity in conductivity makes the semiconductor one of the most important materials for electronic applications.导体如铝和银有高的电导率，典型值从104到106S/cm;而半导体具有的电导率介乎于两者之间。

Superluminescent diode with a broadband gain based on self-assembled InAs quantum dots and segmented contacts for an optical coherence tomography light source Nobuhiko Ozaki, David T. D. Childs, Jayanta Sarma, Timothy S. Roberts, Takuma Yasuda, Hiroshi Shibata, Hirotaka Ohsato, Eiichiro Watanabe, Naoki Ikeda, Yoshimasa Sugimoto, and Richard A. HoggCitation: Journal of Applied Physics 119, 083107 (2016); doi: 10.1063/1.4942640View online: /10.1063/1.4942640View Table of Contents: /content/aip/journal/jap/119/8?ver=pdfcovPublished by the AIP PublishingArticles you may be interested inStructural and optical properties of self-assembled InAs quantum dot molecules on GaAs substratesJ. Vac. Sci. Technol. B 28, 1271 (2010); 10.1116/1.3516010N incorporation into InGaAs cap layer in InAs self-assembled quantum dotsJ. Appl. Phys. 98, 113525 (2005); 10.1063/1.2140891Broadband InGaAs tapered diode laser sources for optical coherence radar and coherence tomographyAppl. Phys. Lett. 86, 191101 (2005); 10.1063/1.1925313Low frequency noise of GaAs Schottky diodes with embedded InAs quantum layer and self-assembled quantum dotsJ. Appl. Phys. 93, 3990 (2003); 10.1063/1.1559412Light emission spectra of columnar-shaped self-assembled InGaAs/GaAs quantum-dot lasers: Effect of homogeneous broadening of the optical gain on lasing characteristicsAppl. Phys. Lett. 74, 1561 (1999); 10.1063/1.123616Superluminescent diode with a broadband gain based on self-assembled InAs quantum dots and segmented contacts for an optical coherence tomography light sourceNobuhiko Ozaki,1,2,a)David T.D.Childs,1Jayanta Sarma,1,b)Timothy S.Roberts,1Takuma Y asuda,2Hiroshi Shibata,2Hirotaka Ohsato,3Eiichiro Watanabe,3Naoki Ikeda,3Y oshimasa Sugimoto,3and Richard A.Hogg 11Department of Electronic and Electrical Engineering,University of Sheffield,Sheffield S37HQ,United Kingdom 2Faculty of Systems Engineering,Wakayama University,Wakayama 640-8510,Japan 3National Institute for Materials Science (NIMS),Tsukuba,Ibaraki 305-0047,Japan(Received 7November 2015;accepted 26January 2016;published online 29February 2016)We report a broadband-gain superluminescent diode (SLD)based on self-assembled InAs quantum dots (QDs)for application in a high-resolution optical coherence tomography (OCT)light source.Four InAs QD layers,with sequentially shifted emission wavelengths achieved by varying the thick-ness of the In 0.2Ga 0.8As strain-reducing capping layers,were embedded in a conventional p-n hetero-junction comprising GaAs and AlGaAs layers.A ridge-type waveguide with segmented contacts was formed on the grown wafer,and an as-cleaved 4-mm-long chip (QD-SLD)was prepared.The seg-mented contacts were effective in applying a high injection current density to the QDs and obtaining emission from excited states of the QDs,resulting in an extension of the bandwidth of the electrolumi-nescence spectrum.In addition,gain spectra deduced with the segmented contacts indicated a broad-band smooth positive gain region spanning 160nm.Furthermore,OCT imaging with the fabricated QD-SLD was performed,and OCT images with an axial resolution of $4l m in air were obtained.These results demonstrate the effectiveness of the QD-SLD with segmented contacts as a high-resolution OCT light source.VC 2016AIP Publishing LLC .[/10.1063/1.4942640]I.INTRODUCTIONNear-infrared (NIR)broadband (low-coherence)lighthas been utilized as a useful probe for non-invasive cross-sectional biological and medical imaging system:optical coherence tomography (OCT).1OCT relies upon low-coherence interferometry,and the axial resolution of OCT is governed by the coherence length of the light source,2which is given by the formula 0.44Âk 02/D k for a low-coherence light with a Gaussian spectral shape.Where the peak in emission is centered at k 0with a bandwidth of D k .As the application is in medical imaging,the center wavelength,k 0,is preferably in the NIR wavelength range as NIR light offers deep penetration into biological samples,and a large imag-ing depth can be obtained.3Thus,a large bandwidth NIR light source is required to obtain an OCT image with high axial resolution and large penetration depth.As a specific criterion,a resolution of 3–5l m is necessary to distinguish single cells.4In commercial OCT systems,a semiconductor-based superluminescent diode (SLD)is often used as a broadband light source.A SLD exhibits amplified spontane-ous emission providing a broader spectral emission range than a laser diode and higher emission power and brightness than a light-emitting diode.However,it is difficult tobroaden the emission bandwidth of a NIR SLD beyond $100nm,which is one of the reasons for the limitation of the axial resolution in an OCT image to around $10l m.Although alternative light sources have been developed for realizing high-resolution OCT,such as the use of a short-pulsed femtosecond laser 5or supercontinuum generation in a photonic crystal fiber,6a SLD still offers the advantages of being a compact,robust,and inexpensive device compared with alternative light sources.To overcome the difficulty of obtaining a broadband-gain SLD,self-assembled quantum dots (QDs)7have been recently recognized as an ideal light-emitting material instead of a con-ventional quantum well (QW)or bulk semiconductor.A QD is a three-dimensionally quantum confined structure and has a unique configuration of electron states and discrete delta-function-like density of states (DOS).8The states can be easily filled with supplied carriers,and the emission bandwidth of the QD should be extended in accordance with their discrete bandgap energies:the ground state (GS),1st excited state (ES1),and 2nd excited state (ES2).In addition,self-assembled InAs QDs on a GaAs substrate,which are grown via the strain induced by a lattice mismatch between InAs and GaAs (Stranski-Krastanov growth mode),9,10are particularly suitable to emit a broadband spectrum in the NIR region because of their size and compositional distributions in the ensemble.A SLD based on InAs QDs (QD-SLD)was first proposed by Wang et al .11and has been intensively studied.12–21We have fabricated a QD-SLD based on InAs QDs with controlled emission wavelengths 21and demonstrated OCT imaging usinga)This research was partly performed while N.Ozaki was at The University of Sheffield as a Visiting Academic.Electronic mail:ozaki@sys.wakayama-u.ac.jp b)Visiting Scholar with Department of Electronic and Electrical Engineering,University of Sheffield,Sheffield S37HQ,United Kingdom.0021-8979/2016/119(8)/083107/7/$30.00VC 2016AIP Publishing LLC 119,083107-1JOURNAL OF APPLIED PHYSICS 119,083107(2016)the developed QD-SLD.22However,the bandwidth of the elec-troluminescence (EL)was limited because the emission was limited to that from GS and ES1due to a limited injection cur-rent density (J )through the use of a single contact electrode.In this work,we thus developed a QD-based SLD,which includes multiple QD layers with deliberately shifted emission wavelengths,with segmented contacts to allow an increase in J locally within the device and to exploit emis-sions from higher energy states of the QDs,i.e.,ES2.The objective of this work was to realize a further broadened and dipless EL spectrum suitable for a high-resolution OCT light source.In addition,we measured gain spectra from the fabri-cated SLD using the segmented contact method 23to examine the gain bandwidth.Furthermore,OCT imaging with the fab-ricated QD-SLD was performed to evaluate its potential use in an OCT light source.II.EXPERIMENTAL DETAILS A.Sample preparationFour stacked InAs QD layers capped with In 0.2Ga 0.8As layers of various thickness were grown by molecular beam epitaxy on an n þ-GaAs (001)substrate,as illustrated inFig.1(a).All the QD layers were grown with a supply of InAs of 2.0monolayers,where the density of the grown QDs was 2–4Â1010cm À2.The In 0.2Ga 0.8As layer deposited on each QD layer was used as a strain-reducing layer (SRL)24to con-trol the emission center wavelength of the QDs by varying its thickness:250,1,2,and 4nm.A 240-nm-thick GaAs wave-guide layer including the QD layers was optically and elec-tronically confined within 1.5-l m-thick p-/n-Al 0.35Ga 0.65As cladding layers.The p-/n-cladding layers were doped at approximately 2.0Â1017cm À3by Be and Si,respectively.A 300-nm-thick p þ-GaAs (doped:$1Â1019cm À3)layer was grown on the upper p-cladding layer as a contact layer to the electrode.A ridge waveguide (RWG)was fabricated normal to cleaved facets with a height of 1.4l m and width of 5l m on the p-side surface of the grown wafer using photolithography and inductively coupled plasma reactive ion etching techni-ques.An insulation film of 200-nm-thick SiO 2was deposited on the surface using plasma-enhanced chemical vapor depo-sition,followed by wet-etching of selective areas (segments)on the RWG with buffered hydrofluoric acid solution.Subsequently,electrodes were formed by depositing Ti/Au (p-contact)and Ni/AuGe/Ni/Au (n-contact),and rapid ther-mal annealing was performed.To form segmented contacts,the electrode of the p-contact was divided into four 1-mm-long electrically isolated segments via the lift-off process,as shown in Fig.1(b).The contact gap lengths between the seg-ments were approximately 40l m.Both edges of the RWG were cleaved to form a 4-mm-long chip,and no anti-reflective (AR)coating was applied to the cleaved edges.B.EL and gain spectra measurementEL emission spectra from an edge of the fabricated RWG were measured at room temperature.Various injection currents (I s)were applied to the contact nearest to the edge (segment 1).The emission light was collected with an optical lensed fiber and was detected with an optical spectrum ana-lyzer,which performs spectrum measurements through tuna-ble bandpass filtering with a monochromator.The coupling loss into the optical lensed fiber was approximately 10dB.The gain spectrum was obtained using the segmented contact method.Based on the following formula,23G ¼1L lnP J ;2L ðÞP J ;L ðÞÀ1 ;(1)the gain and absorption spectra as a function of wavelengthwere determined.P (J ,L )and P (J ,2L )indicate the EL inten-sities obtained from the RWG lengths of L and 2L ,respec-tively,under the same J .Figures 2(a)and 2(b)present schematic diagrams of the device drive geometries;the cur-rent was injected into segment 1only to measure P (J ,L ),and both segments 1and 2were injected with identical J to measure P (J ,2L ).The un-pumped segments are expected to act as absorber elements during the EL measurements and prevent lasing in the device.This feature of the segmented contact can be effective in obtaining a broadband SLDemissionFIG.1.(a)Profile of a fabricated sample.(b)Schematic image and photo-graph of the segmented contacts fabricated on the QD-SLD chip.even though the RWG has a simple straight structure and no AR coating is formed on the facets.C.Spectral-domain OCT imagingA spectral-domain OCT(SD-OCT)26system was uti-lized to evaluate the fabricated chip as an OCT light source. The SD-OCT,which is categorized as a Fourier-domain OCT,27,28enables a spatial reflectivity distribution to be obtained against the depth of a sample along with the optical axis through an inverse Fourier-transformed(IFT)spectrum of interference between reflections from the sample and a refer-ence mirror.As schematically illustrated in Fig.3,the OCT setup consisted of the QD-SLD as a light source,a reference arm,a sample arm,and a spectrometer.Light from the QD-SLD was split by a50:50coupler and introduced into the refer-ence and sample arms.Then,the reflected light from the two arms was recombined by the50:50coupler,and the interfer-ence signal was measured by the spectrometer.The interfer-ence signal sampled as a function of the wavelength was rescaled to the wavenumber,I(k),by the linear interpolation method.The zero-filling method was also used to increase the number of data points on both sides of the spectrum,I(k).29 Subsequently,the IFT spectrum and depth profile of the reflec-tivity in the sample along with the optical axis was obtained.By collecting the depth profile with a lateral scanning of the sample,a2D OCT image was obtained.III.RESULTS AND DISCUSSIONA.EL measurementsFigure4presents the EL spectra obtained from the fabri-cated chip under various I s¼1–150mA,correspondingto FIG.2.Schematic images of device driven with differentlengths.FIG.3.Schematic illustration of SD-OCT setup including the fabricatedQD-SLD chip.FIG.4.(a)–(c)EL spectra obtained from the fabricated QD-SLD chip undervarious I s applied to segment1.(d)Plotted peak wavelength(closed square)and span(solid bar)of the EL emissions.current densities of J¼20–3000A/cm2,which were applied to segment1.As clearly observed in the series of spectra with injected currents(Figs.4(a)–4(c)),the spectral shape and center wavelength varied with the increased current. Initially,1230-nm-centered emission spanning approxi-mately1100–1300nm(the bandwidth was below100nm) was exhibited at lower I s($3mA),as observed in Fig.4(a). Subsequently,1180-nm-centered emission spanning approxi-mately1050–1300nm was exhibited from I¼5–10mA (Fig.4(b)).Finally,the center wavelength blue-shifted up to 1100nm and the emission span extended to$1000nm for I¼150mA(Fig.4(c)).As summarized in Fig.4(d),the peak wavelength(closed square)and emission band(solid bar) were blue-shifted,and the bandwidth was increased from approximately70to120nm with increased I.These behav-iors can be attributed to state-filling effect,where supplied carriersfill the discrete states in the QD in a stepwise man-ner,from lower to higher energy states.Although the observed emission spectra cannot be certainly assigned to specific emission lines from each energy state of the four stacked QDs,the emission spanning1200–1250nm is attrib-uted to electron/hole(e/h)recombination between GSs, and the emissions at approximately1150–1200nm and 1050–1150nm is attributed to ES1and ES2recombinations, respectively.The number of states in the GS is lower than that in the ES1and ES2,and thus,GS emissions can be obtained,even though a low injection current($3mA)is applied.Then,the injection current was increased,and the contribution of ES1emissions began.When their intensity was almost equal to the GS intensity under the injection cur-rent of approximately12.5mA,the bandwidth was increased to120nm.On further increasing the injection current,the ES1emissions were increased while the GS emissions were saturated;then,ES2emissions were sequentially increased, while the ES1and GS emissions were saturated.In order to clarify the state-filling effect,EL intensities at several wavelengths in the spectra are plotted as functions of I,as shown in Fig.5.Ideally,the integral EL intensities of each QD energy state in each layer should be plotted;how-ever,it is difficult to distinguish the emission spectra because of the broad and overlapping nature of emissions from QD ensembles,as described above.We thus utilized the plotted EL intensities as an approximate investigation.The EL intensities at1200and1250nm,which should be dominantly contributed from the GS emissions,were increased for lower I(Շ30mA)and then became gradually saturated for Iտ30mA.On the other hand,the EL intensities at1150and 1100nm increased sequentially after the increment of EL intensities at longer wavelength were decreased.These incre-ments of EL intensities in order of wavelength(state energy) indicate the state-filling in the discrete states,which indicates QD-originated emission.Furthermore,the ratio of the satura-tion currents of the EL intensities can be explained by vary-ing the number of carriersfilling the QD states.The ratio of the number of states for GS:ES1:ES2in a parabolic potential is2:4:6(including spin degeneracy),30and thus,the ratio of the injection currents necessary forfilling the QD states should be2:6:12for GS,GSþES1,and GSþES1þES2.In addition,when the carrier density increases,the Auger pro-cess will occur,and the actual current to saturate these states will increase.The saturation currents of the EL intensities shown in Fig.5vary with respect to the increase in current forfilling the states,e.g.,approximately20mA for the lon-gest wavelength in contrast to above140mA for the shortest wavelength.The wide extended emission wavelength implies the con-tribution of emission from ES2and not only ES1and GS of the QDs.In our previous work,21,22the emission wavelength was extended to approximately$1100nm from a chip with single contact under a current density of400A/cm2.By intro-ducing the segmented contacts,it was possible to increase the current density up to3000A/cm2in a single segment, which is approximately8times higher than that for the previ-ous device,and emission from the higher energy state(ES2) emerged.B.Gain spectraFigure6presents the deduced net modal gain spectra under various I s(applied to a1-mm-long segment of the waveguide)in accordance with Equation(1).The positive or negative values of the net modal gain indicate that the QDs function as optical gain or absorption media at the given wavelength,respectively.As clearly seen in the spectra, positive gain regions occur from approximately1240nm, where the GS emissions were mainly observed and extended continuously to shorter wavelength with increasing I.TheFIG.5.EL intensity plotted for each wavelength as a function of -modal-gain spectra of the QD-SLD under various I s.positive gain region under I of12.5mA was$1183–1237nm and was extended to a range of$1076–1233nm(bandwidth of$160nm)under I of150mA.The extension of the positive gain region with the increase in I can also be attributed to the sequential state-filling effect from GS to ES2,which is dem-onstrated by the dependence of the EL intensities.These results demonstrate that the fabricated chip operates as a gain media because of the QDs.The maximum gain value at I of 150mA was approximately6cmÀ1.The span of the gain region and the maximum gain value were almost the same under I s higher than150mA.This result might be due to the influence of the heat caused by high I s.By introducing a ther-moelectric cooler and a pulsed current source,the maximum gain value can be further increased.Because the emission center wavelength of each QD layer was shifted continuously by the SRL,the broad gain spectra appeared without apparent dips in the positive gain regions of the spectra in contrast to the QD-SLD including QD layers with identical emission center wavelengths of GS and ES.This smooth gain feature is useful in obtaining a broad emission spectrum with homogeneous intensities.The gain values assigned at excited states(ES1and ES2)were higher than that from GS,which is probably due to the higher state degeneracy in the ESs compared with the GS. The possibility of amplified spontaneous emission,that is, stimulated emissions from the states,is proportional to the DOS for the transition of carriers(Fermi’s golden rule).The results above indicate the effectiveness of the segmented contacts for deriving higher ES emission and a broadband-gain.C.OCT imagingA fabricated QD-SLD chip was evaluated as an OCT light source.As described in the Introduction,the axial reso-lution of OCT image is governed by the central wavelength and the bandwidth of the EL spectrum.Figure7(a)presents normalized EL spectra of a QD-SLD under various I s (10–100mA).In order to estimate the axial resolution when the chip was used in OCT,the IFT EL spectra were deduced, as shown in Fig.7(b).The IFT EL spectra provide more accurate estimation of the OCT axial resolution than that from the formula indicated in the Introduction:0.44Âk02/ D k,because this formula is defined for a low-coherence light source with a Gaussian spectrum in the frequency unit. According to the Wiener–Khinchin theorem,a Fourier rela-tionship exists between the autocorrelation function and the power spectrum of the light source.31The autocorrelation, which corresponds to the point-spread function,governs the axial resolution of the OCT image;the axial resolution can be estimated using the full-width at half-maximum(FWHM) of the IFT EL(power)spectra.As observed in the Fig.7(b), the FWHM decreased with increased I.In addition to the increase in the bandwidth of the power spectrum,the blue-shift of the peak wavelength resulted in a decrease of the axial resolution to3.8l m(in air)with an increase of I to 100mA.This estimated axial resolution is less than half of that of typical commercial OCT:$10l m.In addition,no apparent side lobes appeared beside the main peak,which indicates that the ghost images(noise)resulting from the side lobe should be minimized in an OCT image when the QD-SLD is used as a light source.OCT imaging with the QD-SLD was performed for a test sample:a cover-glass plate with a refractive index of1.5 and a thickness of approximately150l m.To produce a two-dimensional OCT image of the sample,depth profiles were obtained by scanning the sample along the in-plane direc-tion.Then,the depth profiles were displayed in two dimen-sions with a gray scale of the signal intensity.Figure8(a) presents the obtained OCT image.Two white lines are clearly seen in the image,which represent reflections at the upper and lower surfaces of the sample.The distance between the lines is approximately220l m,which is consist-ent with the optical path length,that is,the thickness of the cover-glass plate multiplied by its refractive index. Figure8(b)presents a depth profile along the red dashed line in the image.Two peaks resulting from reflections from the surfaces of the cover-glass plate appear in the depth profile. The FWHM of each peak is approximately4l m,and no apparent side lobes appeared beside the peak.These features are consistent with those of the coherence function shown in Fig.7(b).The axial resolution of the OCT image was thus determined to be approximately4l m,which is half of that of our previous result using a QD-SLD with a single con-tact.22This improvement of the axial resolution results from FIG.7.(a)Normalized EL spectrum from a QD-SLD under I s of 10–100mA.(b)Coherence function of the EL spectra shown in(a).the modification of the prepared contacts;the segmented contacts enable an increase of J and extension of the emis-sion wavelength range.Based on the above results,we conclude that the QD-SLD with segmented contacts is a promising light source for high-resolution OCT imaging.In particular,the axial resolu-tion below 4l m in air is expected to distinguish single cells in an OCT image,which is difficult to observe using a con-ventional OCT system.IV.SUMMARYA SLD chip based on self-assembled InAs QDs with seg-mented contacts was developed.EL spectra revealed the extension of the emission band to shorter wavelength with increasing I .This behavior is due to the contribution of higher excited states of the QDs to the emission,which were derived from the state-filling effect under higher I s.The measured op-tical gain of the QDs using the segmented contact method revealed a gain bandwidth beyond 160nm under I of 150mA.The gain bandwidth was also extended to shorter wavelength,corresponding to the contributions of the ESs of the QDs.These results indicate the effectiveness of the segmented con-tacts for deriving emissions of higher excited states of QDs and broadband gain.Furthermore,OCT imaging was per-formed using the QD-SLD,and the potential of the QD-SLD as a light source for high-resolution OCT was demonstrated.ACKNOWLEDGMENTSN.O.would like to thank the members of Richard Hogg’s group at the University of Sheffield for their supportand fruitful discussions about the experimental results.This study was partly supported by Grants-in-Aid for Scientific Research (KAKENHI)Grant No.25286052and the Canon foundation.N.O.would like to acknowledge financial support received from Wakayama University to visit the University of Sheffield.The fabrication of the SLD chip was supported by the NIMS Nanofabrication Platform in the “Nanotechnology Platform Project”sponsored by the Ministry of Education,Culture,Sports,Science,and Technology,Japan (MEXT).1D.Huang,E.A.Swanson,C.P.Lin,J.S.Schuman,W.G.Stinson,W.Chang,M.R.Hee,T.Flotte,K.Gregory,C.A.Puliafito,and J.G.Fujimoto,Science 254,1178(1991).2M. E.Brezinski,Optical Coherence Tomography:Principles and Applications (Academic Press,New York,2006).3M.S.Patterson,B.C.Wilson,and D.R.Wyman,Lasers Med.Sci.6,379(1991).4J.Welzel,Skin Res.Technol.7,1(2001).5W.Drexler,U.Morgner,F.X.K €a rtner,C.Pitris,S.A.Boppart,X.D.Li,E.P.Ippen,and J.G.Fujimoto,Opt.Lett.24,1221(1999).6B.Povazay,heva,A.Unterhuber,B.Hermann,H.Sattmann,A.F.Fercher,W.Drexler,A.Apolonski,W.J.Wadsworth,J.C.Knight,P.St.,J.Russell,M.Vetterlein,and E.Scherzer,Opt.Lett.27,1800(2002).7Self-Assembled Quantum Dots ,Lecture Notes in Nanoscale Science and Technology Series Vol.1,edited by Z.M.Wang (Springer,New York,2008).8Y.Arakawa and H.Sakaki,Appl.Phys.Lett.40,939(1982).9L.Goldstein,F.Glas,J.Y.Marzin,M.N.Charasse,and G.Le Roux,Appl.Phys.Lett.47,1099(1985).10D.Leonardo,M.Krishnamurthy,C.M.Reaves,and P.Petroff,Appl.Phys.Lett.63,3203(1993).11Z.Z.Sun,D.Ding,Q.Gong,W.Zhou,B.Xu,and Z.G.Wang,Opt.Quantum Electron.31,1235(1999).12Z.Y.Zhang,Z.G.Wang,B.Xu,P.Jin,Zh.Sun,and F.Q.Liu,IEEE Photonics Technol.Lett.16,27(2004).13M.Rossetti,A.Markus,A.Fiore,L.Occhi,and C.Velez,IEEE Photonics Technol.Lett.17,540(2005).14S.K.Ray,K.M.Groom,M.D.Beattie,H.Y.Liu,M.Hopkinson,and R.A.Hogg,IEEE Photonics Technol.Lett.18,58(2006).15P.D.L.Greenwood,D.T.D.Childs,K.M.Groom,B.J.Stevens,M.Hopkinson,and R.A.Hogg,IEEE J.Sel.Top.Quantum Electron.15,757(2009).16Z.Y.Zhang,R.A.Hogg,X.Q.Lv,and Z.G.Wang,Adv.Opt.Photonics 2,201(2010).17X.Li,P.Jin,Q.An,Z.Wang,X.Lv,H.Wei,J.Wu,J.Wu,and Z.Wang,Nanoscale Res.Lett.6,625(2011).18N.Yamamoto,K.Akahane,T.Kawanishi,H.Sotobayashi,Y.Yoshioka,and H.Takai,Jpn.J.Appl.Phys.,Part 151,02BG08(2012).19S.Chen,M.Tang,Q.Jiang,J.Wu,V.G.Dorogan,M.Benamara,Y.I.Mazur,G.J.Salamo,P.Smowton,A.Seeds,and H.Liu,ACS Photonics 1,638(2014).20N.Ozaki,T.Yasuda,S.Ohkouchi, E.Watanabe,N.Ikeda,Y.Sugimoto,and R.A.Hogg,Jpn.J.Appl.Phys.,Part 153,04EG10(2014).21T.Yasuda,N.Ozaki,H.Shibata,S.Ohkouchi,N.Ikeda,H.Ohsato,E.Watanabe,Y.Sugimoto,and R.A.Hogg,IEICE Trans.Electron.E99-C ,381(2016).22H.Shibata,N.Ozaki,T.Yasuda,S.Ohkouchi,N.Ikeda,H.Ohsato,E.Watanabe,Y.Sugimoto,K.Furuki,K.Miyaji,and R.A.Hogg,Jpn.J.Appl.Phys.,Part 154,04DG07(2015).23P.Blood,G.M.Lewis,P.M.Smowton,H.Summers,J.Thomson,and J.Lutti,IEEE J.Sel.Top.Quantum Electron.9,1275(2003).24K.Nishi,H.Saito,S.Sugou,and J.-S.Lee,Appl.Phys.Lett.74,1111(1999).25N.Ozaki,K.Takeuchi,Y.Hino,Y.Nakatani,T.Yasuda,S.Ohkouchi,E.Watanabe,H.Ohsato,N.Ikeda,Y.Sugimoto,E.Clarke,and R.A.Hogg,Nanomater.Nanotechnol.4,26(2014).FIG.8.(a)OCT image obtained from a cover-glass plate with a refractive index and thickness of approximately 1.5and 150l m,respectively.Surfaces of the cover-glass are indicated by black arrows.(b)Depth profile along the red dashed line in the OCT image.The FWHM of the peaks indicated by black arrows is $4l m.26Optical Coherence Tomography:Technology and Applications,edited by W.Drexler and J.G.Fujimoto(Springer,New York,2008).27A. F.Fercher, C.K.Hitzenberger,G.Kamp,and S.Y.El-Zaiat, mun.117,43(1995).28G.H€a usler and M.W.Lindner,J.Biomed.Opt.3,21(1998).29C.Dorrer,N.Belabas,J.-P.Likforman,and M.Joffre,J.Opt.Soc.Am.B 17,1795(2000).30A.Wojs,P.Hawrylak,S.Fafard,and L.Jacak,Phys.Rev.B.54,5604 (1996).31L.Cohen,IEEE Signal Proc.Lett.5,292(1998).。

人体静电放电对有机发光二极管的影响张建华;陈章福;徐小雪;曹进;杨连乔【摘要】研究了静电放电(ESD)人体模式(HBM)下的脉冲应力对有机发光二极管(OLED)的性能及寿命的影响,并讨论了相应的物理机制.对比分析了4组OLED在施加ESD放电为0,200,800,1 600 V前后的电学和光学特性,并进行了相应的寿命测试分析.研究发现,OLED器件的光谱对ESD不敏感,随着冲击电压的增大,由于静电打击对载流子的短期抑制效应,OLED的亮度出现轻微下降.在静电冲击电压为200 V和800 V时,伏安特性没有发生变化;当静电冲击电压增至1 600 V时,反向漏电有明显增加.后续的加速寿命实验表明,静电打击对器件的工作寿命没有明显的规律性影响,但是会一定程度提高非本质老化失效的概率.%The electro-static discharge (ESD) performance of the organic light emitting diodes was investigated experimentally at the human body model equivalent pulses by utilizing the transmission line pulsing (TLP) tester.ESD with 200,800,1 600 V was applied on four groups OLEDs.The electrical and optical characteristics of OLEDs were analyzed before and after ESD stress.The lifetime tests were carried out for the fresh samples and the devices undergoing ESD stresses.The experiment results show that the electro-luminescence spectra of OLEDs are insensitive to ESD.Because of the short term inhibition effect of ESD on the carriers,the luminance of OLEDs decreases slightly with the increasing of the strike voltage.When the strike voltages are 200 and 800 V,I-V characteristics of OLEDs don'tchange.When the strike voltage is 1 600 V,the leakage current increases obviously.The accelerated life test results show that ESD has no obviousregular influence on the life of OLEDs,but it will increase the probability of non essential aging failure to a certain extent.【期刊名称】《发光学报》【年(卷),期】2018(039)002【总页数】6页(P169-174)【关键词】OLED;静电打击;寿命【作者】张建华;陈章福;徐小雪;曹进;杨连乔【作者单位】上海大学机电工程与自动化学院新型显示及集成应用教育部重点实验室,上海200072;上海大学机电工程与自动化学院新型显示及集成应用教育部重点实验室,上海200072;上海大学机电工程与自动化学院新型显示及集成应用教育部重点实验室,上海200072;上海大学机电工程与自动化学院新型显示及集成应用教育部重点实验室,上海200072;上海大学机电工程与自动化学院新型显示及集成应用教育部重点实验室,上海200072【正文语种】中文【中图分类】TN383+.1;TN3061 引言有机发光二极管(Organic light-emitting device，OLED)最早报道于1963 年，Pope等[1]用蒽单晶制备了OLED器件。

短波碲镉汞电子雪崩二极管的模拟仿真
张智超;闻娟
【期刊名称】《激光与红外》
【年(卷),期】2018(048)008
【摘要】碲镉汞e-APD器件可用于低弱信号检测,碲镉汞材料工艺、器件工艺及器件结构设计对器件性能非常重要.本文采用silvaco软件对平面PIN结构的短波碲镉汞e-APD器件的暗电流、雪崩增益和量子效率进行了仿真分析.结果表明:1)高工作电压下,器件暗电流的主要成分是带间直接隧穿电流;2)工艺因素引入的接近禁带中心的陷阱能级决定器件在中等偏压下的暗电流特性;3)带间直接隧穿和电子碰撞电离主要发生在低掺杂的雪崩放大区;4)在固定偏压下,器件的暗电流和雪崩增益随着雪崩放大区宽度的上升而减少;5)在固定偏压下,器件的雪崩增益随吸收层厚度的增加而轻微增加,同时量子效率逐渐下降.为实现高性能的短波碲镉汞e-APD器件,需要合理设计器件结构和优化材料生长工艺及器件制造工艺.
【总页数】6页(P1014-1019)
【作者】张智超;闻娟
【作者单位】华北光电技术研究所,北京100015;华北光电技术研究所,北京100015
【正文语种】中文
【中图分类】TN214
【相关文献】
1.碲镉汞雪崩光电二极管探测器 [J], 赵俊;李雄军;王晓璇;庄继胜;韩福忠;
2.MBE生长的PIN结构碲镉汞红外雪崩光电二极管 [J], 顾仁杰;沈川;王伟强;付祥良;郭余英;陈路
3.碲镉汞雪崩光电二极管在激光雷达上的应用 [J], 刘兴新
4.中波碲镉汞雪崩光电二极管的增益特性 [J], 李雄军;庄继胜;赵俊;韩福忠;李立华;李东升;胡彦博;杨登泉;杨超伟;孔金丞;舒恂
5.利用刻蚀工艺制备碲镉汞雪崩光电二极管 [J], 李浩;林春;周松敏;王溪;孙权志因版权原因，仅展示原文概要，查看原文内容请购买。

第 3 期李镔， 等： 微腔效应影响有机发光器件调制带宽特性研究∑i4πd i n i (λ)λ-φt ()λ-φb ()λ=2m π，（1）其中，λ表示波长，φt （λ）和φb （λ）分别表示光经过顶电极和底电极反射后产生的相位移动，m 为模数且仅为整数，d i 为各有机功能层的厚度，n i 为各有机功能层的折射率。

我们计算了光在达到高反射Mg ∶Ag 阴极和半透明Ag 阳极时所发生的反射相移之和，以及光穿过有机层所产生的传输相移曲线，结果如图2（d ）所示。

在反射相移曲线与传输相移曲线的交点位置，法布里-珀罗方程才能成立，因此交点的波长对应于微腔器件的共振波长。

根据图2（d ），微腔器件MOLED -40、MOLED -50和MOLED -60的共振波长分别为512，540，560 nm ，与实际结果（图2（c ））相匹配。

MOLED -40的共振波长为512 nm ，与Ir （ppy ）3的本征发光峰值相符，因而确认了MOLED -40处于最佳谐振腔长。

3.3　器件功率耗散特性由于器件中空穴传输层的空穴迁移率远大于电子传输层的电子迁移率[23]，因此Bphen 厚度的减薄将有助于提高器件的传输特性，从而提高了器件中的电流密度及载流子平衡性。

然而，根据器件的EQE 特性曲线，我们观察到Bphen 厚度的减薄并没有引起显著的EQE 提升。

这表明Bphen 厚度的变化并不是导致EQE 变化的主要原因。

因此，我们认为四组器件在EQE 上的差异主要是由于器件光取出特性的变化导致的。

为了探究器件光取出特性的变化，我们对四组器件中偶极子光源（512 nm ）的功率耗散特性进行了计算。

OLED 的发光可以近似看作是无穷多个偶极子组成。

根据经典电磁学理论，结合器件的多层结构，偶极子的辐射光功率密度K 可以由以下公式计算[24]：K TMv=34Re éëêêêùûúúúu 21-u 2(1+a +TM )(1+a -TM )1-a TM ，（2）K TMh =38Re ，（3）K TEh=38Re éëêêê11-u2()1+a +TE()1-a -TE1-a TEùûúúúú，（4）在上述公式中，Re[…]表示括号内复数的实部。