10.7 : pn接合のバイアス

The p-n junction within an LED requires external biasing to produce light.

Forward biasing involves applying a voltage across the p-n junction with the battery's positive terminal connected to the p-side and the negative terminal to the n-side. The applied voltage opposes the junction potential, reducing the barrier width.

This reduced barrier width enables current flow by increasing majority carrier diffusion. The diffusion current is higher than the drift current, and the net current flows in the forward direction from p to n.

During diffusion, the recombination of electrons and holes in the junction region emits photons, making the LED glow.

In reverse biasing, the battery's positive terminal is connected to the n-side and negative to the p-side.

This prevents the LED from glowing as the applied potential adds to the junction potential, resulting in an increased barrier width and a decreased majority carrier diffusion.

The net current is the small drift current obtained due to minority carriers.

If the reverse bias voltage exceeds a certain threshold, junction breakdown occurs, resulting in a large current flow.