PN junction is formed by joining n-type and p-type Si.
• In practice, n-type crystal is being grown, the process is abruptly altered to grow ptype
Si crystal. The p-side is called anode and n-side is called cathode.
• When no voltage is applied to the diode, electrons from the N-type material fill
holes from the P-type material along the junction between the layers, forming a
depletion zone.
• In a depletion zone, the semiconductor material is returned to its original insulating
state -- all of the holes are filled, so there are no free electrons or empty spaces for
electrons, and charge can't flow.