LED Question & Answers June 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 cells LEDs Zener diodes Schottky diodes None Hint 2). The compound material of semiconductors used in LEDs make use of ___________ elements of periodic table. Group-3 Group-4 Group-5 Both a & c None Hint 3). LEDs operates at _________ bias. Forward Reverse Neutral None of the above None Hint 4). Which color LED was first available commercially? Red Yellow Blue Green None Hint 5). The p-n junction in a LED is made of ____________. Silicon Germanium Gallium Arsenide Gallium None Hint 6). The recombination process in the diodes made of silicon and germanium occur due to ________________. Radiative transition Non-radiative transition Depletion region Cannot say None Hint 7). Recombination of electron-hole produces _________ in LEDs. Photons Protons Nucleus Junction capacitance None Hint 8). The junction in LED is __________ doped. Lightly Heavily Moderately None of the above None Hint 9). The spectral distribution of LED is _____________. Symmetric Asymmetric Linear Non-linear None Hint 10). The power in the LED reaches maximum at ____________. Eg + kT Eg KT After Eg+ kT None Hint 11). For the larger photon energy the power tends to ___________. Zero Increase Decrease Remains constant None Hint 12). The recombination in a semiconductor is of _______ types. Radiative recombination Non Radiative recombination Both a and b Radioactive combination None Hint 13). The recombination in which the photon is emitted is termed as ________. Radiative recombination Non Radiative recombination Both a and b Radioactive combination None Hint 14). The light emitted from the surface of the LED is known as ____________. SLEDs ELEDs Both a and b Photodiode None Hint 15). The light in SLED is emitted through _________. Anode Dielectric window Cathode Substrate None Hint 16). The optical losses in LED are ___________. Reabsorption of generated photon Reflection loss at the semiconductor-air interface Total internal reflection loss All the above None Hint 17). The efficiency in the SLED can be enhanced by _________. Texturing Polishing Blasting Breaking None Hint 18). LED efficiency can be increased by __________ substrates. Transparent to wavelength emitted Backed with a reflective layer Light spreading layer All the above None Hint 19). ________ increases the photon energy as the higher current is passed. Joule heating Carrier Leakage Stimulated energy None of the above None Hint 20). The electrons collected directly by the electrode at another end and the photon is not generated is known as _________. Joule heating Carrier Leakage Stimulated energy None of the above None Hint 21). Stimulated emission is considered as a loss in __________. SLEDs ELEDs Both a and b None of the above None Hint 22). The effect of recombination leading to the emission of light is known as _________. Injection Electroluminescence Chemiluminescence Crystalloluminescence Mechanoluminescence None Hint 23). ____________ is the example of Direct band gap or recombination material. Silicon Germanium Gallium Arsenide Gallium None Hint 24). InGaN/GaN uses _________ substrate. Silicon Germanium Sapphire None of the above None Hint 25). Package material refractive index must ___________ to the semiconductor’s index. Match Doesn’t match Vary depending on situation Data insufficient None Hint LED 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. Direct Indirect Both a & b Can’t determine None Hint 27). The probability of recombination of electron-hole directly is less in ___________. Direct Recombination Indirect Recombination Both a & b Can’t determine None Hint 28). Donor states as the centers for recombination in ____________. Direct Recombination Indirect Recombination Both a & b Cannot say None Hint 29). ____________ is an example for Indirect recombination. Silicon Gallium Phosphorus Gallium Arsenide Gallium None Hint 30). In Gallium Arsenide Phosphorus __________ serve as the center for recombination. Oxygen Nitrogen Carbon Silicon None Hint 31). Band gap energy of the semiconductor materials decides ______________. Wavelength of emitted light Color Both a & b Either a or b None Hint 32). ___________ should satisfy momentum and conservation energy both. Direct Recombination Indirect Recombination Both a & b Can’t determine None Hint 33). The energy emitted by photon must be equal to ___________. Joule heating Carrier Leakage Stimulated energy Semiconductors band gap None Hint 34). LEDs with two semiconductors doped differently but using the similar material is known as _____________. Homojunction LED Heterostructure LED Double heterostructure LED None of the above None Hint 35). ____________ LEDs are realized with different materials of band gap. Homojunction Heterostructure Both a & b None of the above None Hint 36). Which LED is brighter? Homojunction LED Heterostructure LED Both a & b None of the above None Hint 37). To ensure mostly the recombination to take place on the surface of the LED ____________ must be followed. Increase in the substrates doping concentration Increasing the length of Diffusion Both a & b Data Insufficient None Hint 38). To emit the light through surface, doping concentration of the substrate must be _______. Increased Decreased Randomly increase or decrease Depends on situation None Hint 39). Increase in the length of diffusion beyond the critical length the photons in the device may get _________. Recombine Reabsorbed Reflected Recurred None Hint 40). LED must be _______ so that the photons must be emitted without getting reabsorbed. Structured Unstructured Homojunction Heterojunction None Hint 41). _____________ quantifies the efficiency of electrical energy conversion into the optical energy emitted. Internal quantum efficiency External quantum efficiency Power efficiency None of the above None Hint 42). The product of internal radiative efficiency and the extraction efficiency is defined as ____________. Internal quantum efficiency External quantum efficiency Power efficiency None of the above None Hint 43). The external quantum efficiency for semiconductors with indirect band gap is generally lesser than ______. 1% 2% 3% 4% None Hint 44). The internal efficiency is based on _____________. Quality of the material Structure Layer composition All the above None Hint 45). The ratio of the rate of recombination of radiation to the total recombination is known as ______________. Internal quantum efficiency External quantum efficiency Power efficiency None of the above None Hint 46). __________ can be reduced by making use of dome-shape package along with a diode. Reabsorption Recurrence Reflection Critical angle None Hint 47). Designing an LED to support both Reabsorption and reflection of emitted light known as __________. Photon Reabsorption Photon Recurrence Photon Recycling All the above None Hint 48). LEDs made with Aluminum Gallium Arsenide produces _______ colour. Red Yellow Infrared Both a and c None Hint 49). High brightness orange-red color is produced by ___________. Gallium Arsenide Aluminum Gallium Phosphide Aluminum Gallium Arsenide Aluminum Gallium Indium Phosphide None Hint 50). Sapphire substrate produce ________ color in LED. Red Blue Infrared Both a and c None Hint 51). Blue color can be produced by ____________ substrate LEDs. Silicon carbide Gallium nitride Zinc selenide All the above None Hint 52). Diamond glow under ________. Red Visible Infrared Ultraviolet None Hint 53). Blue LEDs have __________ band gap for semiconductors. Small Wide Less Minimum None Hint 54). Who invented first blue LED? Nick Holonyak, jr. Jacques Pankove Rubin Braunstein George Craford None Hint 55). _________________ LEDs used in sterilization and disinfection devices. Red Visible Infrared Ultraviolet None Hint 56). White light LED can be produced by mixing ______ color LEDs. Red and Green Green and Blue Red, Green and Blue Red and Blue None Hint 57). The product obtained after mixing Red, Green and Blue LEDs is known as ____________. Multi-colored Blue LEDs Multi-colored White LEDs Multi-colored Black LEDs None of the above None Hint 58). Multi-colored white LEDs with the mixing of Red, Green and Blue LEDs have ____________. Low quantum efficiency High Quantum efficiency Stimulated energy Power efficient None Hint 59). What is the second method to produce white LEDs? Blending different colors Diffusion of colors Coating All the above None Hint 60). CRI in LEDs stands for ______________. Color Regarding Index Color Recurrence Information Color Rendering Index Color Reflection Information None Hint 61). The application of multiple layers of phosphor consisting different colors can increase ____________. Color Regarding Index Color Recurrence Information Color Rendering Index Color Reflection Information None Hint 62). White LEDs produce using Phosphor coatings are known as ______________. RGB LEDs Multicolored White LEDs Phosphor based White LEDs All the above None Hint 63). Quantum efficiency degrades in ___________. RGB LEDs Multicolored White LEDs Phosphor based White LEDs All the above None Hint 64). Type of Multicolored White LEDs is __________. Di-chromatic Tri-chromatic Tetra-chromatic All the above None Hint 65). What is the key factor to deal with energy efficiency in LEDs? Color stability Color rendering capability Luminous efficiency Both a & b None Hint 66). Which type of white LEDs possess high luminous efficiency but low color rendering capability? Di-chromatic Tri-chromatic Tetra-chromatic All the above None Hint 67). ____________ white LEDs offer high color rendering capability but low luminous efficiency. Di-chromatic Tri-chromatic Tetra-chromatic All the above None Hint 68). ________ maintains fair capabilities of color rendering nad good amount of luminous efficiency. Di-chromatic Tri-chromatic Tetra-chromatic All the above None Hint 69). Although having an easiest way of manufacturing what is the basic limitation of phosphor based LEDs? Stokes Energy loss Color rendering capability Luminous efficiency Stimulation energy None Hint 70). A loss occurred due to the conversion of short wavelength consisting photons to large wavelength photons is known as __________. Stimulating energy loss Scattering loss Stokes energy loss Both a & b None Hint 71). Phosphor coating based white LEDs technique offers __________. Low cost High output Both a and b High quantum efficiency None Hint 72). _______________ substrate is used in the new method to produce white LEDs. Silicon carbide Gallium nitride Zinc selenide All the above None Hint 73). Homoepitaxially grown ZnSe on the substrate on ZnSe emits __________ color light from the active region. Red Green Infrared Blue None Hint 74). Who developed the technique to produce white LEDs by coating the blue light using quantum dots? Nick Holonyak, jr. Michael Bowers Rubin Braunstein George Craford None Hint 75). ____________ are the nano crystals of semiconductors that have unique optical properties. Photons Alpha particle Antiparticle Quantum dots None Hint LED Interview Questions and Answers None 76). Quantum dot LEDs offer ___________. More color options Better color rendering Both a and b Less color options None Hint 77). ______ LEDs offer Full-colour potential. Quantum dot Phosphor based RGB Zinc oxide None Hint 78). ____________ LEDs possess high photoluminescence quantum efficiencies (QEs). Quantum dot Phosphor based RGB Zinc oxide None Hint 79). ____________ are the advantages of quantum dots over organic fluorophers. Band gaps are size tunable Good photo stability Large spin orbit coupling All the above None Hint 80). _________ LEDs offer high external quantum efficiencies over Gallium Nitride. Zinc Selenide Gallium Arsenide Zinc Oxide Both a and b None Hint 81). What are the advantages of Zinc oxide based LEDs over Gallium Nitride? Superior quality of material Improved performance of doping Availability of better alloys All the above None Hint 82). OLED is an acronym of ______________. Organic light emitting diode Operating light encryption diode Optimizing light emitting diode Outsourcing light encryption device None Hint 83). What are the two classes of OLEDs? Small-molecule based LEDs Polymer LEDs Rare-molecular LEDs Both a and b None Hint 84). How many organic layers are present in double-heterostructure of small-molecule OLED? Two Three Four Five None Hint 85). __________________ is the layer adjacent to anode and the cathode in small molecule based LEDs. Electron transport layer Hole transport layer Emissive layer All the above None Hint 86). Light-emitting polymer layer is present in ___________. Small-molecule based LEDs Polymer LEDs Rare-molecular LEDs Both a and b None Hint 87). Organic material of emission possesses conjugated _________. Polymer Photon Electron Pi bonds None Hint 88). _________ known as Flexible OLEDs. Small-molecule based LEDs Regular LEDs Polymer LEDs Can’t say None Hint 89). Light emissive layer made up of biological materials in _________. Small-molecule based LEDs Regular LEDs Polymer LEDs Bio-LEDs None Hint 90). Electrostatic discharge leads to ____________. Failure of the semiconductor junction Permanent shifting of parameters Latent damage All the above None Hint 91). If the AC supply is provided to LED, but they only lights up for _______ voltage. Positive Negative Neutral Ground None Hint 92). The lead of anode in LED is ________. Short Flat Long Sharp None Hint 93). Bi-color LED consists of _______ diodes. One Two Three Four None Hint 94). ____________ have multivibrated integrated circuits in it. Small-molecule based LEDs Flashing LEDs Polymer LEDs Bio-LEDs None Hint 95). LED made using single die is known as ____________. Miniature LED Alphanumeric LED Flashing LED Multi-color LED None Hint 96). LED emission is ________ on temperature. Dependent Independent Can’t say Data insufficient None Hint 97). _________ LEDs are used in remote control systems. Small-molecule based LEDs IR LEDs Polymer LEDs Bio-LEDs None Hint 98).For acne LED phototherapy can be done by using _________ color LEDs. Red Blue Green Either a or b None Hint 99). Organic LEDs in display applications have _________________. Wide viewing angle Power consumption overall will be less Image response will be faster All the above None Hint 100). __________ semiconductor type emits light. Radiative Non-radiative Intrinsic Extrinsic None Hint 101). ______________ have fastest times of transitions. Small-molecule based LEDs IR LEDs Polymer LEDs Bio-LEDs None Hint Read More About RGB LEDs Time's up
