1. p-n Junctions
ECE 2204

2. p-n junctions
When the same semiconductor is used to make the p-type region as the n-type region, the combination is called a homojunction.
When two different semiconductors are used to make the p-n junction, it is called a heterojunction.

3. Continuity of Fermi Energy

4. IT = 0 mA when Va = 0 V
There are, however, carriers flowing constantly across the p-n junction.
drift
e e e
e e e e e e
diffusion
h h h h h h
h h h
diffusion
drift

5. Built-In Voltage
The built-in voltage is the voltage drop associated with the induced electric field between the p and n regions.

6. Questions
How does the built-in voltage change with increasing temperature?
Compare the built-in voltage for
p-n junction (Na = 1018 cm-3, Nd = 1015 cm-3)
p-n junction (Na = 1015 cm-3, Nd = 1018 cm-3)
p-n junction (Na = 1017 cm-3, Nd = 1016 cm-3)
For the same doping concentration, which semiconductor, Ge or Si, does the p-n junction has the smaller built-in voltage?