Question

How do p-n junctions work in semiconductors

Answer 1

One of the crucial keys to solid state electronics is the nature of the P-N junction. When p-type and n-type materials are placed in contact with each other, the junction behaves very differently than either type of material alone. Specifically, current will flow readily in one direction (forward biased) but not in the other (reverse biased), creating the basic diode. This non-reversing behavior arises from the nature of the charge transport process in the two types of materials.

Answer 2

The open circles on the left side of the junction above represent "holes" or deficiencies of electrons in the lattice which can act like positive charge carriers. The solid circles on the right of the junction represent the available electrons from the n-type dopant. Near the junction, electrons diffuse across to combine with holes, creating a "depletion region". The energy level sketch above right is a way to visualize the equilibrium condition of the P-N junction. The upward direction in the diagram represents increasing electron energy.

Answer 3

@radar

Answer 4

The junction is a result of valence structure of two materials that have 4 electrons in the valence band that have been "doped" with an impurity that gives one side of junctionn a "p" flavor (or positive charge carrier) and the other side a "n" flavor or electron (negative charge carrier)The carriers in the p material are called "holes" and in the n meterial "electrons". At the junction there occurs a diffusion process that creates an ionic condition with negative ions on the p side and positive ions on the n side. This area is polarized and is called the depleted region. See this link:
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html

The key to the operation of a transistor which consist of two junctions is the term "minority carrier injection"
While in the FAA, I went to a 4 week class on semiconductors in 1970, but I remember very little of the details. I do remember that quantum levels are involved and there is an important quantum term called "Fermi level" which I have also forgotten.......has something to do with temperature and energy levels.