Which of the following statements are correct in case of Light Emitting Diodes ? (a) Homojunctions LEDs are often surface emitters. (b) Heterojunctions LEDs are Edge emitters. (c) Heterojunction LEDs are often surface emitters. (d) LEDs provide monochromatic & coherent radiations. Options :
(a) & (b) are correct.
To determine which statements about Light Emitting Diodes (LEDs) are correct, let's analyze each statement in relation to known characteristics of LED technology:
- Statement (a): Homojunctions LEDs are often surface emitters.
This statement is correct. Homojunction LEDs typically emit light from the surface of the device, making them surface emitters. The light is emitted due to the recombination of electrons and holes in the semiconductor material, primarily at the surface.
- Statement (b): Heterojunctions LEDs are Edge emitters.
This statement is correct. Heterojunction LEDs are designed to emit light from the edge, referred to as edge emitters. The structure of heterojunctions, often involving layers with different bandgaps, facilitates this type of emission.
- Statement (c): Heterojunction LEDs are often surface emitters.
This statement is incorrect as Heterojunction LEDs, as mentioned previously, are typically edge emitters.
- Statement (d): LEDs provide monochromatic & coherent radiations.
While LEDs do provide monochromatic (single color) radiation due to their narrow emission spectrum, they do not provide coherent light. Coherent light requires the light waves to be in phase, a characteristic of LASERs, not LEDs.
Based on this analysis, the correct answer is:
- (a) & (b) are correct.
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