1. Notes 4 March 2013 Start Chapter 7, “pn Junction”

2. Carrier Transport at the PN Junction
P-type
N-type
P-type
N-type
Depletion region 2 2 2

3. Formation of Depletion Region
Space charge region=depletion region= region depleted of charge carries (electrons or holes)
Space charges: ionized acceptor atoms in the p-side and ionized donor atoms in the n- side. Space charges cannot move. 3 3 3

4. PN Junction Under Equilibrium Condition
— band diagram
Features under equilibrium condition (zero bias):
The Fermi-level is flat throughout the whole junction
The diffusion force is balanced by the internal E-field built by the space charges (this
is why the depletion region is limited) 4 4 4

5. Band Bending and Built-in Potential

8. E-field in the Depletion Region8 8 8

10. Built-in Potential Band bending: Solution for Vbi from Fermi-functions10

12. Width of Depletion Regionxp xn W 12 12