Carrier concentrations of semiconductors were discussed by finding the fermi dirac distribution function and density of states function

1. ANIL NEERUKONDA INSTITUTE OF TECHNOLOGY &
SCIENCES(A)
Department of Electronics and Communication Engineering
ECE 125 Basic Electronics Engineering
 Academic year : 2022-23
 Class & Section : 1/4 ECE-A
 Name of the Faculty : Mr.D.Anil Prasad
ANIL PRASAD DADI/ECE/ANITS

2. UNIT-I(Semiconductor Diodes)
• Fermi level in Intrinsic & Extrinsic semiconductors. Mass-Action law.
Mobility and conductivity, Hall effect, Generation and recombination
of charges, Drift and diffusion current, Band structure of open-circuit
p-n junction, V-I characteristics, transition and diffusion capacitance,
reverse recovery time, Avalanche and zener breakdown, zener
diodes, Light Emitting Diodes.
ANIL PRASAD DADI/ECE/ANITS

3. Contents
• Fermi Dirac distribution function
• Energy bands and fermi level
• Density of states function
• Equilibrium carrier concentrations
• Position of Fermi level
– Intrinsic
– N-type
– P-type
ANIL PRASAD DADI/ECE/ANITS

4. Fermi Dirac distribution function
ANIL PRASAD DADI/ECE/ANITS

5. Fermi level
• Fermi level shows concentration / density of charge carriers in a given
semiconductor at any temperature.
• Fermi level is the energy level below which all energy levels are occupied
by electrons and above it all energy levels are empty at T=00K only
• At any temperature(say 1000K,2000K,3000K etc) we cannot say which
energy levels are filled with electrons above EF due to transition from VB to
CB, which energy levels are unoccupied with electrons below EF is not
known.
ANIL PRASAD DADI/ECE/ANITS

6. Energy bands and Fermi level
ANIL PRASAD DADI/ECE/ANITS

7. Energy bands and Fermi level
ANIL PRASAD DADI/ECE/ANITS
 Slope of CB ,VB or intrinsic fermi level
represents electric field .
 Electric field is directed in positive
slope direction of CB or VB or intrinsic
fermi level.

8. Variation of f(E,T) with temperature
ANIL PRASAD DADI/ECE/ANITS

9. Density of states function
 It represents the number of energy
states available at a given energy in
CB or VB. It is denoted by N(E)
 In a semiconductor moving upwards
in CB the density of states
increases.
 Similarly moving downwards in VB
the density of energy states
increases.
ANIL PRASAD DADI/ECE/ANITS

10. Density of states function
 It represents the number of energy
states available at a given energy in
CB or VB. It is denoted by N(E)
ANIL PRASAD DADI/ECE/ANITS

11. Equilibrium carrier concentration-
electrons
 The electron concentration in CB is
ANIL PRASAD DADI/ECE/ANITS

12. Equilibrium carrier concentration-
electrons
 When E-EF>>3KT, we can approximate the Fermi function as
ANIL PRASAD DADI/ECE/ANITS

13. Equilibrium carrier concentration-
holes
 The hole concentration in VB is
ANIL PRASAD DADI/ECE/ANITS

14. Equilibrium carrier concentrations
 If we add and subtract an intrinsic fermi level
ANIL PRASAD DADI/ECE/ANITS

15. Intrinsic carrier concentration
 In intrinsic semiconductor
concentration of electrons=concentration of holes, n=p=ni
ANIL PRASAD DADI/ECE/ANITS

16. Intrinsic carrier concentration
 In intrinsic semiconductor
ANIL PRASAD DADI/ECE/ANITS

17. Position of Fermi level in Intrinsic
Semiconductor
ANIL PRASAD DADI/ECE/ANITS

18. Position of Fermi level in Intrinsic
Semiconductor
ANIL PRASAD DADI/ECE/ANITS

19. Position of Fermi level in n-type
Semiconductor
ANIL PRASAD DADI/ECE/ANITS

20. Position of Fermi level in p-type
Semiconductor
ANIL PRASAD DADI/ECE/ANITS

21. References
ANIL PRASAD DADI/ECE/ANITS
• Robert L Boylestad, Electronic Devices And Circuit Theory, Prentice
Hall, seventh edition,2021
• Jacob Millman and Christos Halkias, Electronics Devices and
Circuits, Black edition, October,2017

22. Thank you
for listening
ANIL PRASAD DADI/ECE/ANITS