1. Chapter II Semiconductor Physics
半導體物理

2. Basic Semiconductor Physics
Carrier Transport
Drift
Diffusion
Generation and Recombination
Current density equation
Thermionic Emission
Tunneling
High Field Effects
Heterojunction
Quantum Well

3. Carrier Drift Carrier Drift (飄移)
Carrier transport in an applied electric field
vn = -nE
vp = pE
n (p): carrier mobility (移動率)
(cm2/V-s)
Drift Current Density
J = (qnn + qpp)E

4. Mobility and Resistivity (Conductivity)
 = -1 = [q(n n + pp)]-1
-1 = L-1 + I-1

5. Scattering Lattice Scattering Impurity Scattering
Thermal vibration of lattice
L ~ T-3/2
Impurity Scattering
Carrier scattered by impurities (donors or acceptor)
I ~ T3/2/NT
The main factors in influence of resistance of solid-state materials are:
Carrier concentration
scattering

6. Carrier Diffusion Carrier Diffusion (擴散)
The carriers tend to move from a region of high concentration to a region of low concentration.
Diffusion Current Density
Jn = qDn (dn/dx)
Dn: diffusivity (diffusion coefficient)
Einstein relation: Dn = ( kT/q)n)

7. Induced Electric Field (Built-in Field )in a semiconductor
For a semiconductor that is non-uniformly doped with donor impurity atoms and is in thermal equilibrium, there exists an induced electric field Ex in this semiconductor.
Built-in voltage in a p-n junction diode
Accelerating field in a graded-base bipolar junction transistor EC EF EV x

8. Current Density Equations
Jn = qnnE + qDn (dn/dx)
Jp = qppE - qDp (dp/dx)
J = Jn + Jp

9. Carrier Generation and Recombination
Direct generation and recombination of electron-hole pairs:
at thermal equilibrium.
under illumination
Decay of photoexcited carriers

10. Indirect Generation-Recombination Process
Indirect G-R process at thermal equilibrium

11. 其他重要的專有名詞 Carrier lifetime Diffusion Length Recombination center
Surface recombination
Auger recombination
Auger process: an electron and a hole recombine, giving up the excess energy to an electron (producing a “hot” electron), and then the hot electron eventually loses its energy by emitting phonons (i.e. giving up heating)
Auger recombination is an important non-radiative recombination, especially in materials with narrow bandgap.

12. Thermionic Emission 當電子的能量大於qX時,它就可以被熱離子式地發射至真空能階. 金屬與半導體之間主要的載子傳輸機制
單載子元件(unipolar device)的電流形成模型

13. Tunneling The transmission coefficient T
There is a finite probability that a particle impinging a potential barrier will penetrate the barrier.

14. High-field effects Saturation velocity in Si
Transferred-electron effect in GaAs
Avalanche Breakdown
Ionization

15. Avalanche Breakdown Zener breakdown Avalanche breakdown
field ionization
heavily doped p/n region
VBD < 5V
VBD has a NTC
Avalanche breakdown
impact ionization
Low or medium doped p/n region
VBD > 7V
VBD has a PTC

16. Transferred-electron effect

17. Heterojunction
Junction formed by two different semiconductors (different EG)
Under thermal equilibrium:
Gradient of EF = 0
Continuous vacuum level
Specific EC and EV
EC = χ2 –χ1
EV = EG – (χ2 –χ1)

18. Quantum Well Quantum structures Quantum-sized effect
2D: Quantum Well
1D: Quantum Wire
0D: Quantum Dot
Quantum-sized effect
Quantum-confined effect
Quantum Well
W-N-W heterojunction multi-layer structure with a very thin narrow-bandgap semiconductor
Energy band split into discrete quantized energy levels
Red laser diode in GaAs

19. 2DEG in Heterojunction Structure
Two-Dimensional Electron Gas
Electrons will spill over the AlGaAs into the GaAs and become trapped in the potential well, called 2DEG
Very high mobility electrons with negligible impurity scattering
Devices in which conduction occurs parallel to the interface can be construct from 2DEG structure.

20. 2DEG in Quantum Well
Quantum Well
Heterojunction