LED Question & AnswersJune 5, 2021 By WatElectronics This article lists 100+ LED MCQs for engineering students. All the LED Questions & Answers given below include a hint and wherever possible link to the relevant topic. This is helpful for the users who are preparing for their exams, interviews, or professionals who would like to brush up their fundamentals on the LED topic.The optical semiconductor device purpose is to convert electrical energy to light energy. These are broadly classified into two different groups: Light receiving devices (Example: Solar cells) and Luminescent devices (Example: Light-emitting diodes and the LASER diodes). In comparison to the LASER diodes, LEDs are low in cost and offer a longer service life. The very first commercially available LED was used to replace the indicator lamps made of neon and incandescent lamps. Nick Holonyak, Jr. was the first to invent the LED that is capable of producing visible-spectrum red light. These LEDs are further classified as Surface emitting LEDs (SLEDs) and Edge emitting LEDs (ELEDs). 1). ____________ replaced neon indicator and incandescent lamps.Solar cellsLEDsZener diodesSchottky diodesHintLess energy is utilized by LED 2). The compound material of semiconductors used in LEDs make use of ___________ elements of periodic table.Group-3Group-4Group-5Both a & cHintGallium Arsenide, Gallium Phosphide 3). LEDs operates at _________ bias.ForwardReverseNeutralNone of the aboveHintLight is emitted when the forward voltages are applied 4). Which color LED was first available commercially?RedYellowBlueGreenHintLEDs developed initially were used as Indicators 5). The p-n junction in a LED is made of ____________.SiliconGermaniumGallium ArsenideGalliumHintLED cannot use germanium and silicon 6). The recombination process in the diodes made of silicon and germanium occur due to ________________.Radiative transitionNon-radiative transitionDepletion regionCannot sayHintNo emission of a photon 7). Recombination of electron-hole produces _________ in LEDs.PhotonsProtonsNucleusJunction capacitanceHintSemiconductor to produce photons 8). The junction in LED is __________ doped.LightlyHeavilyModeratelyNone of the aboveHintThe p and n junction of LEDs are heavily doped 9). The spectral distribution of LED is _____________.SymmetricAsymmetricLinearNon-linearHintPlot between power and the photon energy 10). The power in the LED reaches maximum at ____________.Eg + kTEgKTAfter Eg+ kTHintPhoton energy increases and reaches Eg +kT the power becomes maximum 11). For the larger photon energy the power tends to ___________.ZeroIncreaseDecreaseRemains constantHintThe power tends to decrease exponentially 12). The recombination in a semiconductor is of _______ types.Radiative recombinationNon Radiative recombinationBoth a and bRadioactive combinationHintRecombinations are classified based on the emission of a photon 13). The recombination in which the photon is emitted is termed as ________.Radiative recombinationNon Radiative recombinationBoth a and bRadioactive combinationHintNon-radiative recombination is the term to indicate that photon is not emitted 14). The light emitted from the surface of the LED is known as ____________.SLEDsELEDsBoth a and bPhotodiodeHintLEDs based on the way of emission classified into two types 15). The light in SLED is emitted through _________.AnodeDielectric windowCathodeSubstrateHintDisplay applications, SLEDs are used 16). The optical losses in LED are ___________.Reabsorption of generated photonReflection loss at the semiconductor-air interfaceTotal internal reflection lossAll the aboveHintThe losses affect the extraction efficiency in the LED. 17). The efficiency in the SLED can be enhanced by _________.TexturingPolishingBlastingBreakingHintMaking uneven the surface of SLED 18). LED efficiency can be increased by __________ substrates.Transparent to wavelength emittedBacked with a reflective layerLight spreading layerAll the aboveHintSubstrate's effectiveness to emit light 19). ________ increases the photon energy as the higher current is passed.Joule heatingCarrier LeakageStimulated energyNone of the aboveHintDue to the passage of high currents the device gets heated 20). The electrons collected directly by the electrode at another end and the photon is not generated is known as _________.Joule heatingCarrier LeakageStimulated energyNone of the aboveHintCarrier leakage loss leads to saturation 21). Stimulated emission is considered as a loss in __________.SLEDsELEDsBoth a and bNone of the aboveHintSLEDs emit light through the surface 22). The effect of recombination leading to the emission of light is known as _________.Injection ElectroluminescenceChemiluminescenceCrystalloluminescenceMechanoluminescenceHintRadiative recombination 23). ____________ is the example of Direct band gap or recombination material.SiliconGermaniumGallium ArsenideGalliumHintsemiconductor involved in Radiative recombination 24). InGaN/GaN uses _________ substrate.SiliconGermaniumSapphireNone of the aboveHintCommercial LEDs do prefer sapphire substrates 25). Package material refractive index must ___________ to the semiconductor’s index.MatchDoesn’t matchVary depending on situationData insufficientHintRefractive index doesn't match the light, it partially reflects the semiconductorLED Multiple Choice Question & Answers 26). In __________ recombination, the free electrons at the conduction band bottom can directly recombine with the free holes present at the valence band top.DirectIndirectBoth a & bCan’t determineHint Direct recombination 27). The probability of recombination of electron-hole directly is less in ___________.Direct RecombinationIndirect RecombinationBoth a & bCan’t determineHintDifferences in momentum 28). Donor states as the centers for recombination in ____________.Direct RecombinationIndirect RecombinationBoth a & bCannot sayHintAdditional impurities added in the Indirect recombination 29). ____________ is an example for Indirect recombination.SiliconGallium PhosphorusGallium ArsenideGalliumHintGallium Phosphorus is the semiconductor 30). In Gallium Arsenide Phosphorus __________ serve as the center for recombination.OxygenNitrogenCarbonSiliconHintA donor state is created by adding impurities 31). Band gap energy of the semiconductor materials decides ______________.Wavelength of emitted lightColorBoth a & bEither a or bHintBand gap energy of the semiconductor materials 32). ___________ should satisfy momentum and conservation energy both.Direct RecombinationIndirect RecombinationBoth a & bCan’t determineHintMomentum and the Conservation energy both must be satisfied 33). The energy emitted by photon must be equal to ___________.Joule heatingCarrier LeakageStimulated energySemiconductors band gapHintBand gap energy of semiconductor 34). LEDs with two semiconductors doped differently but using the similar material is known as _____________.Homojunction LEDHeterostructure LEDDouble heterostructure LEDNone of the aboveHintHomojunction LEDs are doped differently 35). ____________ LEDs are realized with different materials of band gap.HomojunctionHeterostructureBoth a & bNone of the aboveHintLEDs doped differently with different materials of the band gap 36). Which LED is brighter?Homojunction LEDHeterostructure LEDBoth a & bNone of the aboveHintHeterostructure LEDs are brighter 37). To ensure mostly the recombination to take place on the surface of the LED ____________ must be followed.Increase in the substrates doping concentrationIncreasing the length of DiffusionBoth a & bData InsufficientHintStructure of LED plays a major role in the emission of light 38). To emit the light through surface, doping concentration of the substrate must be _______.IncreasedDecreasedRandomly increase or decreaseDepends on situationHintIncrease in the substrate's doping concentration 39). Increase in the length of diffusion beyond the critical length the photons in the device may get _________.RecombineReabsorbedReflectedRecurredHintProbability that photons may get reabsorbed 40). LED must be _______ so that the photons must be emitted without getting reabsorbed.StructuredUnstructuredHomojunctionHeterojunctionHintStructured LEDs increase the emission 41). _____________ quantifies the efficiency of electrical energy conversion into the optical energy emitted.Internal quantum efficiencyExternal quantum efficiencyPower efficiencyNone of the aboveHint External quantum efficiency 42). The product of internal radiative efficiency and the extraction efficiency is defined as ____________.Internal quantum efficiencyExternal quantum efficiencyPower efficiencyNone of the aboveHintExternal quantum efficiency 43). The external quantum efficiency for semiconductors with indirect band gap is generally lesser than ______.1%2%3%4%HintExternal quantum efficiency for an indirect bandgap of semiconductors must be lesser than 1% 44). The internal efficiency is based on _____________.Quality of the materialStructureLayer compositionAll the aboveHint Materials quality, structure, and the composition of the layer 45). The ratio of the rate of recombination of radiation to the total recombination is known as ______________.Internal quantum efficiencyExternal quantum efficiencyPower efficiencyNone of the aboveHintStructure, material quality, and the layer's composition 46). __________ can be reduced by making use of dome-shape package along with a diode.ReabsorptionRecurrenceReflectionCritical angleHintThe rays outgoing from the diode strikes the dome perpendicularly 47). Designing an LED to support both Reabsorption and reflection of emitted light known as __________.Photon ReabsorptionPhoton RecurrencePhoton RecyclingAll the aboveHintRecycling 48). LEDs made with Aluminum Gallium Arsenide produces _______ colour.RedYellowInfraredBoth a and cHintAluminum Gallium Arsenide produces both 49). High brightness orange-red color is produced by ___________.Gallium ArsenideAluminum Gallium PhosphideAluminum Gallium ArsenideAluminum Gallium Indium PhosphideHintAluminum Gallium Indium Phosphide can produce colors 50). Sapphire substrate produce ________ color in LED.RedBlueInfraredBoth a and cHintBlue color 51). Blue color can be produced by ____________ substrate LEDs.Silicon carbideGallium nitrideZinc selenideAll the aboveHintSilicon under development, Zinc selenide, and Gallium nitride 52). Diamond glow under ________.RedVisibleInfraredUltravioletHintBlue color 53). Blue LEDs have __________ band gap for semiconductors.SmallWideLessMinimumHintGallium nitride possess a wide bandgap 54). Who invented first blue LED?Nick Holonyak, jr.Jacques PankoveRubin BraunsteinGeorge CrafordHintInventor of the LED made with Gallium nitride 55). _________________ LEDs used in sterilization and disinfection devices.RedVisibleInfraredUltravioletHintUV LEDs that emit 250-270nm 56). White light LED can be produced by mixing ______ color LEDs.Red and GreenGreen and BlueRed, Green and BlueRed and BlueHintMixing Red, Green, and Blue color LEDs 57). The product obtained after mixing Red, Green and Blue LEDs is known as ____________.Multi-colored Blue LEDsMulti-colored White LEDsMulti-colored Black LEDsNone of the aboveHintRGB LEDs 58). Multi-colored white LEDs with the mixing of Red, Green and Blue LEDs have ____________.Low quantum efficiencyHigh Quantum efficiencyStimulated energyPower efficientHintWhite LEDs possess higher quantum efficiency 59). What is the second method to produce white LEDs?Blending different colorsDiffusion of colorsCoatingAll the aboveHintPhosphor coating 60). CRI in LEDs stands for ______________.Color Regarding IndexColor Recurrence InformationColor Rendering IndexColor Reflection InformationHintColor Rendering Index determines the way color is interpreted 61). The application of multiple layers of phosphor consisting different colors can increase ____________.Color Regarding IndexColor Recurrence InformationColor Rendering IndexColor Reflection InformationHintColor Rendering Index determines the way color is interpreted 62). White LEDs produce using Phosphor coatings are known as ______________.RGB LEDsMulticolored White LEDsPhosphor based White LEDsAll the aboveHintSever layers of distinct color phosphor coatings 63). Quantum efficiency degrades in ___________.RGB LEDsMulticolored White LEDsPhosphor based White LEDsAll the aboveHintMultiple layers of phosphor coating 64). Type of Multicolored White LEDs is __________.Di-chromaticTri-chromaticTetra-chromaticAll the aboveHintTypes of white LEDs 65). What is the key factor to deal with energy efficiency in LEDs?Color stabilityColor rendering capabilityLuminous efficiencyBoth a & bHintThe luminous flux per unit electrical power applied at the input 66). Which type of white LEDs possess high luminous efficiency but low color rendering capability?Di-chromaticTri-chromaticTetra-chromaticAll the aboveHintDi-chromatic white LEDs is about 120 lm/W 67). ____________ white LEDs offer high color rendering capability but low luminous efficiency.Di-chromaticTri-chromaticTetra-chromaticAll the aboveHintTetra-chromatic LEDs 68). ________ maintains fair capabilities of color rendering nad good amount of luminous efficiency.Di-chromaticTri-chromaticTetra-chromaticAll the aboveHintLuminous efficiency > 70 lm/w 69). Although having an easiest way of manufacturing what is the basic limitation of phosphor based LEDs?Stokes Energy lossColor rendering capabilityLuminous efficiencyStimulation energyHintStokes energy 70). A loss occurred due to the conversion of short wavelength consisting photons to large wavelength photons is known as __________.Stimulating energy lossScattering lossStokes energy lossBoth a & bHintLimitation of phosphor-based white LEDs 71). Phosphor coating based white LEDs technique offers __________.Low costHigh outputBoth a and bHigh quantum efficiencyHintLow cost and produces high output 72). _______________ substrate is used in the new method to produce white LEDs.Silicon carbideGallium nitrideZinc selenideAll the aboveHintNew method to manufacture white LEDs 73). Homoepitaxially grown ZnSe on the substrate on ZnSe emits __________ color light from the active region.RedGreenInfraredBlueHintActive region emits blue light 74). Who developed the technique to produce white LEDs by coating the blue light using quantum dots?Nick Holonyak, jr.Michael BowersRubin BraunsteinGeorge CrafordHintCoating a blue LED with quantum dots 75). ____________ are the nano crystals of semiconductors that have unique optical properties.PhotonsAlpha particleAntiparticleQuantum dotsHint Quantum dots can be used to tune the color emitted LED Interview Questions and Answers 76). Quantum dot LEDs offer ___________.More color optionsBetter color renderingBoth a and bLess color optionsHintTuning property of quantum dots 77). ______ LEDs offer Full-colour potential.Quantum dotPhosphor basedRGBZinc oxideHint Zinc oxide-based LEDs 78). ____________ LEDs possess high photoluminescence quantum efficiencies (QEs).Quantum dotPhosphor basedRGBZinc oxideHintHigh QEs are offered due to the quantum dots 79). ____________ are the advantages of quantum dots over organic fluorophers.Band gaps are size tunableGood photo stabilityLarge spin orbit couplingAll the aboveHintHighly resistant to chemical/ photo-degradation 80). _________ LEDs offer high external quantum efficiencies over Gallium Nitride.Zinc SelenideGallium ArsenideZinc OxideBoth a and bHintEQE three times higher in comparison to Gallium Nitride 81). What are the advantages of Zinc oxide based LEDs over Gallium Nitride?Superior quality of materialImproved performance of dopingAvailability of better alloysAll the aboveHintThree times higher external quantum efficiencies 82). OLED is an acronym of ______________.Organic light emitting diodeOperating light encryption diodeOptimizing light emitting diodeOutsourcing light encryption deviceHintArranging organic films in series amid two conductors 83). What are the two classes of OLEDs?Small-molecule based LEDsPolymer LEDsRare-molecular LEDsBoth a and bHintOLEDs consist of two main classes 84). How many organic layers are present in double-heterostructure of small-molecule OLED?TwoThreeFourFiveHintThree layers present in double-heterostructure small molecule-based LEDs 85). __________________ is the layer adjacent to anode and the cathode in small molecule based LEDs.Electron transport layerHole transport layerEmissive layerAll the aboveHintTransport layer reduces the free charge carrier's recombination 86). Light-emitting polymer layer is present in ___________.Small-molecule based LEDsPolymer LEDsRare-molecular LEDsBoth a and bHintLEP layer combines the emitter, host, and transport functions 87). Organic material of emission possesses conjugated _________.PolymerPhotonElectronPi bondsHintPresence of conjugated pi-bonds 88). _________ known as Flexible OLEDs.Small-molecule based LEDsRegular LEDsPolymer LEDsCan’t sayHintPLEDs are lighter 89). Light emissive layer made up of biological materials in _________.Small-molecule based LEDsRegular LEDsPolymer LEDsBio-LEDsHintEnvironmentally friendly and biodegradable 90). Electrostatic discharge leads to ____________.Failure of the semiconductor junctionPermanent shifting of parametersLatent damageAll the aboveHintIncreases the rate of degradation 91). If the AC supply is provided to LED, but they only lights up for _______ voltage.PositiveNegativeNeutralGroundHintForward-biased 92). The lead of anode in LED is ________.ShortFlatLongSharpHintCathode terminal has short lead-in LEDs 93). Bi-color LED consists of _______ diodes.OneTwoThreeFourHintInversely parallel 94). ____________ have multivibrated integrated circuits in it.Small-molecule based LEDsFlashing LEDsPolymer LEDsBio-LEDsHintFlashing LEDs flash for a duration of one second 95). LED made using single die is known as ____________.Miniature LEDAlphanumeric LEDFlashing LEDMulti-color LEDHintMiniature LEDs are used as indicators 96). LED emission is ________ on temperature.DependentIndependentCan’t sayData insufficientHintDepends on both ambient temperature and the device temperature 97). _________ LEDs are used in remote control systems.Small-molecule based LEDsIR LEDsPolymer LEDsBio-LEDsHintOptical fibers, free-space-optical communication 98).For acne LED phototherapy can be done by using _________ color LEDs.RedBlueGreenEither a or bHintRed or blue color 99). Organic LEDs in display applications have _________________.Wide viewing anglePower consumption overall will be lessImage response will be fasterAll the aboveHintLEDs can generate light directly 100). __________ semiconductor type emits light.RadiativeNon-radiativeIntrinsicExtrinsicHintMaterials undergo recombination 101). ______________ have fastest times of transitions.Small-molecule based LEDsIR LEDsPolymer LEDsBio-LEDsHintIR LEDs have low amounts of forwarding voltagesRead More About RGB LEDs Time is Up!