forwardbiasing

Forward biasing is a condition in semiconductor devices, primarily diodes and transistors, where an external voltage is applied in such a way that it reduces the potential barrier across the junction. For a p-n junction diode, forward biasing occurs when the positive terminal of a voltage source is connected to the p-type semiconductor and the negative terminal is connected to the n-type semiconductor. This applied voltage opposes the internal built-in potential of the junction.

When forward bias is applied, the majority carriers from both sides of the junction are pushed towards the depletion region. Electrons from the n-side and holes from the p-side are injected across the junction. This injection of carriers effectively narrows the depletion region and lowers the potential barrier. As the forward bias voltage increases, more carriers are injected, and the junction's resistance decreases.

Once the forward bias voltage exceeds a certain threshold, known as the turn-on voltage or knee voltage, a significant current begins to flow through the diode. This current is primarily due to the movement of majority carriers across the junction. The turn-on voltage depends on the type of semiconductor material; for silicon diodes, it is typically around 0.7 volts, while for germanium diodes, it is around 0.3 volts. In this state, the diode acts as a low-resistance path, allowing current to pass with minimal opposition. This is in contrast to reverse biasing, where the depletion region widens and a very small leakage current flows.