RONETTE S. GARCIABSEE-IV

*Introduction to Optoelectronics

Outline* What is optoelectronics? Major optoelectronic devices Processes and Function

What Did the Word Opto-Electronics Mean?Optoelectronics is the study and application of electronic devices that interact with light*

Optoelectronicsis the study and application ofelectronicdevices that source, detect and controllight, usually considered a sub-field ofphotonics. In this context,lightoften includes invisible forms of radiation such asgamma rays,X-rays,ultravioletandinfrared, in addition to visible light. Optoelectronic devices are electrical-to-optical or optical-to-electricaltransducers, or instruments that use such devices in their operation.Electro-opticsis often erroneously used as a synonym, but is in fact a wider branch ofphysicsthat deals with all interactions between light andelectric fields, whether or not they form part of an electronic device.*

Examples of Optoelectronic Devices*

Major Optoelectronic Devices Direct Conversion Between Electrons and Photons*Light-emitting diodes (LEDs) (display, lighting,)Laser diodes (LDs) (data storage, telecommunication, )Photodiodes (PDs) (telecommunication, )Solar Cells (energy conversion)

Light-Emitting Diodes (LEDs)*Light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction.

Photon Emission in Semiconductor*When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. The wavelength of the light depends on the band gap of the semiconductor material Semiconductor materials: Si, Ge, GaAs, InGaAs, AlGaAs, InP, SiGe, etc

Operation Principle of LED*

Semiconductor Materials vs. LED Color*

General Brightness GaP GaN GaAs GaAIAs -- Green, Red Blue Red, Infrared Red, Infrared -- Super Brightness GaAIAs GaAsP GaN InGaN GaP Red Red, Yellow Blue Green Green Ultra Brightness GaAIAs InGaAIP GaN InGaN -- Red Red, Yellow, Orange Blue Green --

Application of LEDs* Display Solid-state lighting Communication Remote control, etcLED lights on an Audi S6

LasersSpontaneous emission and stimulated emissionApplication of LasersClassification of lasers according to the way of pumpingLaser diodesWhat is semiconductor? p/n junction diodeLight emitting diode and laser diode

Spontaneous and stimulated emissionSpontaneous emissionLight emission by relaxation from the excited state to the ground statestimulated emissionLight emission due to optical transition forced by optical stimulation; This phenomenon is the laser=light amplification by stimulated emission of radiation

Optical transitionTransition occurs from the ground state 1 to the excited state 2 with the probability of P12 by the perturbation of the electric field of light: This is an optical absorption.The excited state 2 relaxes to the ground state 1 spontaneously with a light emission to achieve thermal equilibriumEnergy12Spontaneous emission

Stimulated emissionTransition from the excited state 2 to the ground state 1 occurs by the stimulation of the electric field of incident light with the transition probability of P21(=P12), leading to emission of a photon. This process is called stimulated emission.The number of photons is doubled since first photon is not absorbed. 12p12Stimulated emissionEnergyE

Emission is masked by absorption under normal conditionUnder normal condition stimulated emission cannot be observed since absorption occurs at the same probability as emission (P12=P21), and the population N1 at 1 dominates N2 at 2 due to Maxwell-Boltzmann distribution. Therefore, N2P21

population inversion for lasingIn order to obtain net emission (N2P21>N1P12), N2, the population of the state 2 should exceed N1, the population of the state 1.This is called population inversion, or negative temperature, since the distribution feature behaves as if the temperature were negative.

Characteristics of laserOscillator and amplifier of light waveWave-packets share the same phase leading to Coherence: two different lasers can make interference fringesDirectivity: laser beam can go straight for a long distanceMonochromaticity: laser wavelength is pure with narrow widthHigh energy density: laser can heat a substance by focusingUltra short pulse: laser pulse duration can be reduced as short as femtosecond (10-15 s)Bose condensation quantum state appearing macroscopically

Application of lasersOptical CommunicationsOptical StoragesLaser PrintersDiplaysLaser ProcessingMedical Treatments

Optical fiber communication

Optical StoragesCDDVDBDMDMO

Laser Printershttp://web.canon.jp/technology/detail/lbp/laser_unit/index.html

Laser ShowPolygon mirror

Laser ProcessingWeb site of Fujitsu

Laser Diodes (LDs)*Lasers (Light Amplification by Stimulated Emission)

Laser Cavity Design*

Photo Diodes (PDs)*A photodiode is a semiconductor diode that functions as a photodetector. It is a p-n junction or p-i-n structure. When a photon of sufficient energy strikes the diode, it excites an electron thereby creating a mobile electron and a positively charged electron hole

Principle of operation

A photodiode is ap-n junctionorPIN structure. When aphotonof sufficient energy strikes the diode, it creates anelectron,holepair. This mechanism is also known as the innerphotoelectric effect. If the absorption occurs in the junction'sdepletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. Thus holes move toward theanode, and electrons toward thecathode, and aphotocurrentis produced. The total current through the photodiode is the sum of the dark current (current that flows with or without light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device.

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Operation Principle of a PD*

PDs Detection Range and Materials*

MaterialWavelength range (nm)Silicon (Si)1901100Germanium (Ge)4001700Indium gallium arsenide (InGaAs)

Lead sulfide (PbS) 8002600

Vision of Solar Cells (Photovoltaics)Photovoltaics(PV) is a method ofgenerating electrical powerby convertingsolar radiationintodirect current electricityusingsemiconductorsthat exhibit thephotovoltaic effect. Photovoltaic power generation employs solar panelscomposed of a number ofsolar cellscontaining a photovoltaic material. Materials presently used for photovoltaics includemonocrystalline silicon,polycrystalline silicon,amorphous silicon,cadmium telluride, andcopper indium gallium selenide/sulfide. Due to the increased demand forrenewable energysources, the manufacturing of solar cells andphotovoltaic arrayshas advanced considerably in recent years.*

Solar Energy Spectrum*Spectrum of the solar energySolar radiation outside the earths surface:1.35 kW/m2, 6500 times larger than worlds energy demandAM0: radiation above the earths atmosphereAM1.5: radiation at the earths surface Blackbody radiation: ideal radiation

Vision of Solar Cells (Photovoltaics)*

Operation Principle of Solar Cells*

Residential and Commercial Applications*Challenges: cost reduction via: a) economy of scales b) building integration and c) high efficiency cells

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Thank you *

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