1-3. pn junction

Before discussing Schottky barrier diodes (SBDs), let us learn how a pn junction works since it is the most basic junction for forming a diode.
When p-type and n-type semiconductors are joined together, their Fermi levels become equal. This creates a difference in potential between the lower edges of the conduction bands of the n-type and p-type semiconductors (V_CN and V_CP respectively). This difference in potential is called the diffusion potential (V_D) or built-in potential.
Electrons are the majority charge carriers in the n-type semiconductor whereas holes are the majority charge carriers in the p-type semiconductor. Near the junction, electrons in the n-type semiconductor and holes in the p-type semiconductor are attracted and bound to each other and disappear, creating a region called a depletion layer where no carrier exists. Then, some electrons in the n-type semiconductor diffuse into the p-type semiconductor as they have energy exceeding V_D. Therefore, above V_D, the electron densities in both semiconductors become equal. Likewise, some holes in the p-type semiconductor diffuse into the n-type semiconductor. The current that flows as a result of diffusion of charge carriers (electrons and holes) is called diffusion current. The application of voltage (i.e., an electric field) across the junction also causes drift current to flow. However, the diffusion current is dominant except in a depletion region. When the pn junction is unbiased, current stops flowing once the junction reaches an equilibrium state.