Consider 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?

This question was previously asked in
ESE Electronics 2011 Paper 1: Official Paper
View all UPSC IES Papers >
  1. 1, 2. 3 and 4
  2. 1 and 2 only
  3. 3 and 4 only
  4. 2 and 3 only

Answer (Detailed Solution Below)

Option 4 : 2 and 3 only
Free
ST 1: UPSC ESE (IES) Civil - Building Materials
6.1 K Users
20 Questions 40 Marks 24 Mins

Detailed Solution

Download Solution PDF

Explanation:

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.

Latest UPSC IES Updates

Last updated on May 28, 2025

->  UPSC ESE admit card 2025 for the prelims exam has been released. 

-> The UPSC IES Prelims 2025 will be held on 8th June 2025.

-> The selection process includes a Prelims and a Mains Examination, followed by a Personality Test/Interview.

-> Candidates should attempt the UPSC IES mock tests to increase their efficiency. The UPSC IES previous year papers can be downloaded here.

Get Free Access Now
Hot Links: teen patti star apk teen patti download apk teen patti