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 ee e eeeee diffusion h hhhhh h hh 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?