Detailed Summary
The p-n junction is a fundamental component in semiconductor electronics, formed by joining p-type and n-type semiconductor materials. The process starts with a p-type silicon (Si) wafer, where an appropriate amount of pentavalent impurities is introduced to create an n-type region within it. This creates a metallurgical junction, where two important processes occur: diffusion and drift.
In diffusion, electrons migrate from the n-type region (where they are in higher concentration) to the p-type region, while holes move from the p-type region to the n-type region. This movement of charge carriers establishes a diffusion current across the junction. Meanwhile, as electrons leave the n-region, they generate a positive charge (due to ionized donor atoms), and as holes move from the p-side, they create a negative charge (from ionized acceptors). Together, these reactions lead to the formation of a depletion region, devoid of free charge carriers, characterized by immobile ion cores.
As the depletion region expands, an electric field is established, which causes a drift current opposite to the diffusion current. This process continues until the drift current is equal to the diffusion current, indicating the formation of an equilibrium state in the junction with no net current flow. The p-n junction is essential for the operation of devices such as diodes and transistors, as the potential barrier established across the junction controls the current flow based on external voltage application.