pn Junction

The interface between a p-type semiconductor and an n-type semiconductor is called a pn junction. When a p-type semiconductor and an n-type semiconductor are joined (not actually joined, but formed by doping so that they are adjacent to each other), the carriers, holes and free electrons, are attracted to each other and combine and disappear near the boundary. Since there are no carriers in this area, it is called a depletion layer and is in the same state as an insulator. (No bias state)

• Forward direction (connect the positive pole to the p-type region and the negative pole to the n-type region and apply voltage):
  When the applied voltage is gradually increased and exceeds the forward voltage (about 0.7V for silicon Si), electrons flow one after another from the n-type region to the p-type region, and electrons that do not combine with holes and disappear move to the positive pole, allowing current to flow. For an explanation of the physical properties of a pn junction, see the following e-learning.
  Basics of Schottky Barrier Diodes 1-3. pn junction
  
  
• Reverse direction (connect the negative pole to the p-type region and the positive pole to the n-type region and apply voltage):
  No current flows. In the normal voltage range, the excess electrons in the n-type semiconductor move away from the boundary surface. The holes in the p-type semiconductor also move away from the boundary surface. This causes the depletion layer near the boundary surface to expand. However, if a voltage exceeding the breakdown voltage is applied, the pn junction enters a breakdown state due to the Zener effect (avalanche effect) and current flows suddenly. In a typical diode, this breakdown causes the performance to deteriorate and be destroyed.