PN Junction Diode

(In last blog we have seen about Semiconductors and now we are gonna look out PN Junction diode.)

        Normally, PN junctions are manufactured from a single crystal with different dopant concentrations diffused across it. Once PN junction is made it looks like this.

        On the left side, it is P type semiconductor and the right side it is N type semiconductor. In P type, we have more no of holes and and in N type we have more no of free electrons. So in any material, which carriers is more, they known as 'majority carriers' and which are less, they known as 'minority carriers'. In p-type, holes are majority carriers and electrons are minority carriers. This is reverse in N type materials. Holes are represented by unfilled circles and electrons are represented by thick circles. Now what represent unfilled circles with - and + sign?? They are new to us and we check them.

      Imagine we use Si-P (Silicon-Phosphorous) materials for N type and Si-B (Silicon-Boron) materials for P-Type

      When creating PN junction, holes and electrons of both P and N materials respectively near the boundary area diffuse into other material each other (P diffuse to N and N diffuse to P). At that time, free electron of Si-P atoms will fill the electron deficiency in Si-B atoms. So Si-P atoms lose one electron and thus gain one positive charge (represented by unfilled circles with + sign). As same, Si-B atoms gain one electron and thus gain one negative charge (unfilled circles with - sign). This is called 'Space charge Creation'. Atoms which have lost/gain electrons become charged and they posses an electric field. This electric filed will inhibit further diffusion of holes and electrons cross PN junction boundary and ultimately avoid more space charge creation. A PN junction is look like this:

  

         This is called as "PN Junction Diode" and basic part of electronics. We see biasing of diodes in next post.

Thanks and Regards,

Arun Alagarsamy @ arunvasan@gmail.com