Question
Download Solution PDFConsider the following statements:
1. The efficiency of a light emitting diode (LED) decreases with the injected current.
2. The efficiency of a LED increases with a decrease in temperature.
3. The light emitted is connected near the junction because most of the carriers are within a diffusion length of the junction.
4. Light is emitted in a LED when electrons move from the valence band to the conduction band.
Which of these statements are correct?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFExplanation:
LED works on the principle of Electroluminence i.e conversion of electrical energy into light energy.
- In LED, light is emitted due to a large number of recombinations at the junction.
- LEDs are generally fabricated with direct bandgap semiconductors.
- They always operate under forward bias and under reverse biased condition LED work as a normal diode.
From the above points, we can say statement (3) is true.
The efficiency of LED is given by:
\(η=\frac{Ihν}{pq}\)
Where
I is injected current
h = plank's constant
q = charge
ν = frequency
p = incident optical power.
So efficiency is directly proportional to injected current,
Hence η of LED increases with an increase in injected current,
So statement (1) is false.
The efficiency of LED is inversely proportional to temperature.
The emission intensity of LEDs decreases with increasing temperature.
This decrease of the emission intensity is due to several temperature-dependent factors including:
• Non-radiative recombination via deep levels.
• Surface recombination.
• Carrier loss over heterostructure barriers.
Hence statement (2) is true.
Light is emitted in a LED when electrons fall from a higher energy state (conduction band) to a lower energy state (valence band).
Hence statement (4) is false.
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