Direct and Indirect Band Gap Semiconductors - GATE ECE Engineering (ECE)

Test: Direct & Indirect Band Gap Semiconductors - Question 1

Silicon is not suitable for fabrication of light emitting diodes because it is:

A.
An indirect band gap semiconductor
B.
A direct band gap semiconductor
C.
A wide band gap semiconductor
D.
A narrow band gap semiconductor

Detailed Solution: Question 1

Basic LED diode is represented as:

The selection of emission of color from the LED is fairly limited due to the nature of the semiconductor used.
Commonly available colors of LED are red, green, blue, yellow, amber, and white.
Light Emitting Diode (LED) works on the principle of Electroluminescence.
It is the conversion of electrical energy into light energy.
In LED, most of the light is concentrated near the junction because charge carriers will be very close and less than the diffusion length.
LEDs are generally fabricated with Direct Band Gap (DBG) semiconductors like GaAs, GaAsP, GaP.

Direct Band Gap (DBG) Semiconductors:
The semiconductor in which the top of the valence band and the bottom of the conduction band occur at the same value of momentum.

Since Silicon is an Indirect Band Gap semiconductor so electron cannot fall directly to the valence band but must undergo a momentum change as well as a change in energy. So, energy is released as heat along with light. Hence, silicon is not suitable for the fabrication of LEDs.

Test: Direct & Indirect Band Gap Semiconductors - Question 2

Direction: Question consists of two statements, one labeled as the 'Assertion (A)' and the other as 'Reason (R)'. Examine these two statements carefully and select the answer to this question using the codes given below:
Assertion (A): Many semiconductors where minimum energy in the conduction band and maximum energy in the valence band occur at the same value of (wave vector), are preferred for optical lenses.
Reason (R): For such semiconductors, the efficiency of carrier generation and recombination is very high.

A.
Both A and R are individually true and R is the correct explanation of A
B.
Both A and R are individually true but R is not the correct explanation of A
C.
A is true but R is false
D.
A is false but R is true

Detailed Solution: Question 2

Assertion Explanation-
A direct band-gap (DBG) semiconductor is one in which the maximum energy level of the valence band aligns with the minimum energy level of the conduction band with respect to momentum as shown in the figure.

Reason Explanation-
In a DBG semiconductor, direct recombination takes place with the release of the energy equal to the energy difference between the recombining particles. The probability of radiative recombination is high in the case of DBG semiconductors. Hence the efficiency factor of a DBG semiconductor is high. That’s why DBG semiconductors are always preferred for making optical sources.
Note- Best example of direct bandgap semiconductors is GaAs, InAs, InSb, GaN, InN, ZnO, CdSe, ZnS.

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Test: Direct & Indirect Band Gap Semiconductors - Question 3

Which of the following is used to make Light Emitting Diodes (LED)?

A.
Direct Bandgap Semiconductors
B.
Indirect Bandgap Semiconductors
C.
Large Bandgap
D.
Small Bandgap

Detailed Solution: Question 3

Light emitting diodes are made using the semiconductors that have direct bandgap.
The photon emitted when an electron transits from the bottom of conduction band to top of valence band falls into the visible light range.

However, in case of Indirect Bandgap semiconductors, the photon emitted does not fall into the visible light range.

*Answer can only contain numeric values

Test: Direct & Indirect Band Gap Semiconductors - Question 4

If one makes an LED in a semiconductor with a direct bandgap of 2.5eV, the wavelength of light emitted will be ________μm. (Given, Planck’s constant is 6.626x10^-34 J-s and velocity of light is 3x10⁸ m/s)

Detailed Solution: Question 4

Test: Direct & Indirect Band Gap Semiconductors - Question 5

Which of the following is the best photo sensitive material?

A.
CdS
B.
Se
C.
ZnS
D.
PbS

Detailed Solution: Question 5

Cadmium sulphide is best photo sensitive material.

Test: Direct & Indirect Band Gap Semiconductors - Question 6

A particular green LED emits light of wavelength 5490ºA. The energy band gap of the semiconductor material used there is (Planck’s constant = 6.626×10^-34J-s)

A.
2.26 eV
B.
1.98 eV
C.
1.17 eV
D.
0.74 eV

Detailed Solution: Question 6

In eV gap E_g = E/e = 3.62 x 10^-19/1.6 x 10^-19 = 2.26 eV

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Direct & Indirect Band Gap Semiconductors - Free MCQ Practice Test

MCQ Practice Test & Solutions: Test: Direct & Indirect Band Gap Semiconductors (6 Questions)

Silicon is not suitable for fabrication of light emitting diodes because it is:

Which of the following is used to make Light Emitting Diodes (LED)?

If one makes an LED in a semiconductor with a direct bandgap of 2.5eV, the wavelength of light emitted will be ________μm. (Given, Planck’s constant is 6.626x10^-34 J-s and velocity of light is 3x10⁸ m/s)

Which of the following is the best photo sensitive material?

A particular green LED emits light of wavelength 5490ºA. The energy band gap of the semiconductor material used there is (Planck’s constant = 6.626×10^-34J-s)

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Direct & Indirect Band Gap Semiconductors - Free MCQ Practice Test

MCQ Practice Test & Solutions: Test: Direct & Indirect Band Gap Semiconductors (6 Questions)

Silicon is not suitable for fabrication of light emitting diodes because it is:

Which of the following is used to make Light Emitting Diodes (LED)?

If one makes an LED in a semiconductor with a direct bandgap of 2.5eV, the wavelength of light emitted will be ________μm. (Given, Planck’s constant is 6.626x10-34 J-s and velocity of light is 3x108 m/s)

Which of the following is the best photo sensitive material?

A particular green LED emits light of wavelength 5490ºA. The energy band gap of the semiconductor material used there is (Planck’s constant = 6.626×10-34 J-s)

Electronic Devices

Electronic Devices

Top Courses for Electronics and Communication Engineering (ECE)

About this Electronics and Communication Engineering (ECE) Practice Test

Explore more Electronics and Communication Engineering (ECE) Study Resources

If one makes an LED in a semiconductor with a direct bandgap of 2.5eV, the wavelength of light emitted will be ________μm. (Given, Planck’s constant is 6.626x10^-34 J-s and velocity of light is 3x10⁸ m/s)

A particular green LED emits light of wavelength 5490ºA. The energy band gap of the semiconductor material used there is (Planck’s constant = 6.626×10^-34J-s)