1. Properties of Semiconductors
Lecture 5.0
Properties of Semiconductors

2. Importance to Silicon Chips
Size of devices
Doping thickness/size
Depletion Zone Size
Electron Tunneling dimension
Chip Cooling- Device Density
Heat Capacity
Thermal Conductivity

3. Band theory of Semiconductors
Forbidden Zone – ENERGY GAP
Conduction
Band
Valence
Band

4. Silicon Band Structure - [Ne]3s23p2

5. Fermi-Dirac Probability Distribution for electron energy, E
Probability, F(E)=
(e{[E-Ef]/kBT}+1)-1
Ef is the
Fermi Energy

6. Number of Occupied States
Density of States
Fermi-Dirac
T>0

7. Difference between Semiconductors and Insulators
kBT = eV
at 298˚K
Material
Eg(eV)
InSb
0.18
InAs
0.36 Ge
0.67 Si
1.12
GaAs
1.43
SiC
2.3
ZnS
3.6
NiO
4.2
Al2O3 8

8. Probability of electrons in Conduction Band
Lowest Energy in CB
E-Ef  Eg/2
Probability in CB
F(E)= (exp{[E-Ef]/kBT} +1)-1 )
= (exp{Eg/2kBT} +1)-1
 exp{-Eg/2kBT} for Eg>1 298K
kBT = eV
at 298˚K

9. Variation of Conductivity with T
=d/dT

10. Intrinsic Conductivity of Semiconductor
Charge Carriers
Electrons
Holes
= ne e e + nh e h
# electrons = # holes
  ne e (e+ h)
ne  C exp{-Eg/2kBT}
ne=2(2 m*e kBT/h2)3/2 exp(-Eg /(2kBT))
Ef=Eg/2+3/4kBT ln(m*h/m*e)

11. Mobilities

12. Semiconductor Photoelectric Effect
Light Absorption/Light Emission (photodetector)/(photo diode laser)
Absorption max =hc/Eg

13. Light Emitting Diode

14. Photodiode Laser Color depends on band gap, Eg  =hc/Eg
Eg>3.0 transparent
Pb IR
detectors

15. Diode Laser

16. Extrinsic Conductivity of Semiconductor
Donor Doping Acceptor Doping
n-type p-type
N=nd+ni
p= 2(2 m*h kBT/h2)3/2 exp(-Ef/kBT)
Law of Mass Action, Nipi=ndpd or =nndn

17. Extrinsic Conductivity of Semiconductor
Donor Doping Acceptor Doping

18. Electron Density Dopant Concentration effects Electron Density
Electrical Conductivity

19. Conductivity Intrinsic Range Extrinsic Range = ne e e + nh e h
Exponential with T
Extrinsic Range
Promoted to CB
 
Decreasing , 
Joins Intrinsic  
Majority/minority Carriers
= ne e e + nh e h

20. Majority/minority Carriers
Conductivity
= ne e e + nh e h
n-type ne>>nh
Low number of holes due to recombination.
Law of Mass Action
Nipi=ndpd
(For p-type Nipi =nndn )

21. Extrinsic Conductivity of Semiconductor
Donor Doping Acceptor Doping
n-type p-type
Ed = -m*e e4/(8 (o)2 h2)
Ef=Eg-Ed/2
Ef=Eg+Ea/2

22. Effective Mass
Holes
Electrons

23. Wafer Sales
Following PRIME GRADE Si wafers are all single-side polish $14.50 each for 25 wafers each $11.00 for 50 or more (we can double side polish)
4" P<111> ohm-cm
4" N<100> ohm-cm
4" P<111> ohm-cm
4" P<100> ohm-cm
4" P<111> ohm-cm

24. GaP Wafer
2" Undoped (100) $ each
2" S doped (111) $ each

25. C&ENews
1/6/03