Diode Biasing Conditions Explained

A semiconductor diode is a two-terminal electronic component that conducts current primarily in one direction. The behavior of a diode depends heavily on how voltage is applied across its terminals, a process known as biasing.

There are three main biasing conditions for a diode:

• Forward Biased: An external voltage is applied such that the positive terminal is connected to the p-type material and the negative terminal to the n-type material. This reduces the depletion region width and allows significant current to flow. This condition requires an external energy source.
• Reverse Biased: An external voltage is applied such that the negative terminal is connected to the p-type material and the positive terminal to the n-type material. This increases the depletion region width and prevents significant current flow (except for a small leakage current). This condition also requires an external energy source.
• Zero Biased: No external voltage is applied across the diode terminals. In this state, the depletion region exists due to the diffusion of carriers, and there is no external force to drive current. Only a thermal equilibrium is maintained.

The question asks about the condition when no external energy source is applied to the diode. Based on the descriptions above:

• Forward biasing and reverse biasing both require an external voltage source.
• Zero biasing is the condition where no external voltage source is applied.

Therefore, when a diode is under zero bias, no external energy source is applied.