PN Junction

Q1: How do I make a PN junction?
A1: You can physically interface a p-type and n-type semiconductor together. The plane along which they meet is a PN junction.

Q2: Why would I want to make a PN junction?
A2: At least 1 PN junction is used in nearly every semiconductor device.

Q3: What's so special about the PN junction?
A3: In the neighborhood of where p-type and n-type semiconductors are in contact with each other, some of the holes from the p-type semiconductor combine with the free electrons from the n-type semiconductor. Where this neutralization of charge carriers occurs is called the depletion layer.

Q4: Why should I care about the depletion layer?
A4: The depletion layer is where the ionized acceptor and donor atoms come into play. The separation of negatively-charged acceptor atoms and positively-charged donor atoms establishes an electric field in the N to P direction across junction. This internal electric field prevents further diffusion of charge carriers across the junction. The potential difference across the junction is called the junction voltage.