The attached narrated power point presentation mentions the different materials used for the construction of semiconductors. It offers structural and energy level explanation on the properties exhibited by the semiconductor materials. It also throws light on the structure and behaviour of a PN junction and use of PN junctions in active electronic components. The material will be useful for KTU first year students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.
3. 3
Definitions
• Energy Band : The range of energies
possessed by an electron in a solid.
• Valence Electron : Electrons in the
outermost orbit of an atom.
• Valence Band : Range of energies
possessed by valence band electrons.
• Conduction Band : Range of energies
possessed by free electrons.
4. 4
Definitions
• Fermi Level :
- highest energy level that an electron can
occupy at the absolute zero temperature.
- lies between valence and conduction
bands at absolute zero temperature.
- tends to change as solids are warmed.
- value of Fermi level at absolute zero
temperature known as Fermi energy.
5. 5
Definitions
• Forbidden Energy Gap :
- gap between valence band and
conduction band.
- electron can be moved from valence
band to conduction band by applying
energy more than forbidden energy
gap.
• Hole : absence of an electron, +ve charge.
7. 7
Fermi Level in Solids
Top of the collection of electron energy levels at absolute zero temperature.
8. 8
Semiconductors
• Resistivity: 10-5 to 106 Ωm.
• Conductivity: 105 to 10-6 mho/m.
• Temperature coefficient of resistance:
Negative.
• Current Flow: Due to electrons and holes.
• Materials: Silicon, Germanium, Gallium
Arsenide.
20. 20
PN Junction
Concentration gradient
causes carriers to move
to the other side of the
junction.
Potential Barrier
opposes carrier movement.
Junction
Depletion Region
Forward bias reduces
the width, reverse bias
increases the width.
Immobile ions
VB = 0.7 V for Si.
= 0.3 V for Ge.
Holes Electrons
21. 21
Biasing a PN Junction
• Forward Bias – Positive terminal of the
battery connected to the P - type material,
negative terminal of the battery connected
to N - type material.
• Current flow during forward bias.
• Reverse Bias – Positive terminal of the
battery connected to the N - type material,
negative terminal of the battery connected
to P - type material.
• No current flow during reverse bias.