Electronic Devices and Circuit - Lecture Slides, Slides of Electrical and Electronics Engineering

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ELECTRONIC DEVICES AND CIRCUITS

Prepared By: Mr. V. R.Seshagiri Rao,Professor Mr. M. Ramesh Babu, Professor, Mr. D. Khalandar Basha, Associate Professor, Ms. C. Deepthi, Associate Professor

Unit-

PN Junction Diode & Special Function

Electronic Devices

Valence Electrons

• Electrons are distributed in various shells at different distances from nucleus
• Electron energy increases as shell radius increases.
• Electrons in the outer most Shell are called as valence electrons
• Elements in the period table are grouped according to the number of valence electrons.

Valence Electrons

Silicon Crystal

• → At 0°K, each electron is in its lowest possible energy state, and each covalent bounding position is filled.
• →If a small electric field is applied, the electrons will not move → silicon is an insulator

Silicon Atom Diagram at 0°K

Silicon Atom Diagram at Ambiant

Temp

Insulators/Conductors

• Materials that have large bandgap energies (in the range of 3 to 6 electron-volts (eV)) are insulators , because at room temperature, essentially no free electron exists in the material
• Materials that contain very large number of free electrons at room temperature are conductors

Movement of Holes Movement of Holes

Semiconductor Constants

• The concentration of electrons and holes directly influence the magnitde of the current
• In an intrinsic semiconductor (a single crystal semiconductor) the densities of holes and electrons are equal.

Semiconductor Constants

Extrinsic Semiconductor / Doping

• The electron or hole concentration can be greatly increased by adding controlled amounts of certain impurities
• For silicon, it is desirable to use impurities from the group III and V.
• An N-type semiconductor can be created by adding phosphorus or arsenic

N-Type Semiconductor

P-Type Semiconductor