Usage: Positive for forward bias, negative for reverse bias. It is assumed that the forward threshold voltage (knee voltage) for the semiconductor is 0.7V and the reverse breakdown voltage is 10V.
Prerequisites: A basic understanding of the P-N Junction Diode and how its depletion region behaves.
Theory: The depletion region acts as a capacitor. As long as there is some width of the depletion region, current cannot flow.
Applying a higher potential to P-type and lower to N-type repels the majority carriers of P-type (holes) and N-type (electrons) towards the depletion region and the region shrinks. Due to the design of the semiconductor, the region shrinks to an effective width of 0 when it the potential reaches 1.8V in the forward direction.
Conversely, applying a lower potential to P-type and higher to N-type attracts the majority carriers towards the end, away from the depletion region. The depletion region increases in width and conduction is not possible. However, when a very high voltage (greater than 50V) is applied, the depletion region expands to the whole of the diode. Once this happens, conduction starts through the carriers present in the depletion region.
- Width of the depletion region increases with the square of the voltage applied. For the sake of simplicity, it increases linearly here.
- Reverse breakdown voltage varies on the order of 50 - 70V for common diodes. For easier visualization, a 10V breakdown voltage is used in here.