Why cannot we use Si and Ge in fabrication of visible LEDs ?

The energy gap for Si is 1 . 1 eV and for Ge is 0 . 7 eV . Both of the semiconductor are having energy gap less than 1 . 8 eV . Thus, instead of producing photon of visible wavelength, they produce heat in the form of Infrared rays. Hence, Si and Ge are not used in fabrication of visible LEDs.

Three photo diodes D 1 , D 2 and D 3 are made of semiconductors having band gaps of 2 . 5 eV , 2 eV and 3 eV , respectively. Which ones will be able to detect light of wavelength 600 n m ? Given Planck constant is h = 6 . 62 × 10 - 34 m 2 k g s - 1 ,speed of light c = 3 × 10 8 m s - 1

Given that: λ = 600 n m = 600 × 10 - 9 m E = h c λ = 6 . 62 × 10 - 34 × 3 × 10 8 600 × 10 - 9 × 1 . 6 × 10 - 19 eV = 6 . 62 × 3 × 10 - 34 + 8 6 × 1 . 6 × 10 - 26 eV = 2 . 06 eV The incident radiation is detected by photodiode D 2 has band gap or knee voltage 2 eV only which is less than incident radiation of 2 . 06 eV . The photo diode is able to detect the light of given wavelength, if the energy of incident radiation is more than the band gap of the photo diode. Therefore, D 1 and D 3 are not able to detect incident light.

E M B I B E

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 16

EASY

12th Karnataka Board

IMPORTANT

Earn 100

Explain the working of photo-diode.

Important Questions on Semiconductor Electronics: Materials, Devices and Simple Circuits

EASY

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 17

Explain the working of LED.

EASY

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 18

What is a solar cell? Explain its working.

EASY

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 19

When pentavalent impurities are added to germanium, what type of semiconductor is obtained?

EASY

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 20

Draw the

V - I

characteristic for LED and explain its working.

EASY

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 21

State any four applications of LED's,

MEDIUM

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 22

How does the reverse current in a photodiode vary with the intensity of light?

HARD

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 23

The output of an unregulated dc power supply needs to be regulated. Name the device that can be used for this purpose and draw the relevant circuit diagram.

EASY

12th Karnataka Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits>Exercise>Q 24

What is avalanche diode?