Pn junction

1
P-n junction
2
P-n junction in semiconductors
Equilibrium Occurs when Chemical potentials are
equalized ?N ?P
3
Chemical potential (Fermi energy) equalization
4
Built in potential
Built in potential ?(x) is applied to Ec,Ev,Ei
P
Boundary conditions at x-?
5
Depletion region
6
Depletion region
7
P-n junction under bias
Reverse bias
Drift currents
P
Drift current does not depend on the voltage
across the junction
Forward bias
8
Junction current
Diode equation
Saturation current density
9
Junction current
10
Junction capacitance
Reverse bias
11
Junction capacitance
C-V measurement
12
Rigorous treatment of forward bias junction
Quasi-Fermi levels EFN,EFP are continuous through
depletion level
13
Diffusion current
Hole current
Electron current
14
Diode currents
15
Recombination current
16
Maximum recombination
Minimize
Traps near the mid gap
Minimize
Traps near the metallurgical junction
17
Maximum recombination
18
Recombination current
19
Ideality factor
20
Generation current
eV/kTltlt0 n,p0
Maximize G
Generation current
21
Small signal analysis
Differential conductance
Differential resistance
22
Diffusion capacitance
Concentration of injected holes
Injected charge (per cm2)
Diffusion capacitance
Characteristic time constant
weighted recombination time
23
Diffusion capacitance (rigorous)
AC Diffusion equation
24
Diffusion capacitance
Formally
25
Diode switching
At tlt0
One-sided junction
IF
IR
26
Avalanche breakdown
e1
e2
e1
hh
Incremental current
assume
27
Avalanche breakdown condition
Breakdown voltage
28
Tunneling breakdown -Zener Diode
29
Zener diode -applications
Equivalent circuit
V
Zener shunt regulator
30
Zener shunt regulator