19.2 PN Junction and Semiconductor Diode
When an N-type and a P-type semiconductor are joined together, they form a PN junction semiconductor diode. At the junction, electrons from the N-side and holes from the P-side recombine, creating a region without free charge carriers called the depletion region. This region acts as a barrier that prevents further movement of charges. To allow current to flow, an external voltage is applied to overcome this barrier. For silicon-based diodes, the required voltage is about 0.7 V, and for germanium-based diodes, it is about 0.3 V.
lightbulbA diode is like a one-way road for current — allowing it to flow in only one direction and blocking it in the opposite direction.