P-N Junction ‒ Forward Bias

The P-N junction is the foundation of most semiconductor devices, such as diodes, solar cells, LEDs, transistors, and integrated circuits. A diode controls current flow, allowing or preventing current through a circuit depending on the polarity of the applied voltage. When the polarity of a battery allows current to flow through the diode, it is said to be forward-biased. In this forward-biased state, the external voltage causes electrons to move from the negative terminal of the power supply, through the diode, and toward the positive terminal. This injects electrons into the N-type material, increasing the number of free electrons and reducing the size of the depletion layer. Simultaneously, the positive terminal pulls electrons from the P-type material, increasing the number of holes and further reducing the depletion layer. As a result, the external voltage reduces the barrier voltage of the P-N junction. If the applied voltage is greater than the barrier voltage, it will overcome this barrier, allowing current to flow through the diode.