Forward Bias P-N Junction Diode

The p-n junction is said to be forward-biased when the p-type is connected to the positive terminal of the battery and the n-type to the negative terminal. The built-in electric field at the p-n junction and the applied electric field are in opposing directions when the p-n junction is forward biased.

When any type of P-N junction is in forward bias, a resistor Rs must be connected in series with the diode.The function of the limiting resistance is to limit the forward current into the diode.

Under forward bias the field of the space charge region and forward voltage Vd will oppose each other. Hence, the resultant electric field is very small, and it is experimentally found that the field is always directed from N to P.When the P-N junction is forward bias, the barrier height reduces by |V0|(magnitude of VD).

Circuit Diagram of Forward Bias P-N Junction

The following is the illustration for circuit diagram of forward bias P-N Junction:

IV Curve For Forward Bias P-N Junction Diode

In forward biasing, forward current flows in the circuit. When the forward voltage equals zero, the value of forward current is also 0 mA. There is an increase in the current in forward bias diodes with increase in forward voltage till the point known as knee voltage. Beyond this point, the forward current increases rapidly.

Learn more about: IV Characterstics of PN Junction Diode.

Different Cases of Forward Bias

There are three cases for

• Case 1: If V_D< V₀

Barrier voltage (V₀) is dominating. Hence, no majority carrier will be crossing the junction.

• Case 2: If V_D >V₀

In this case, since the forward voltage of the diode which means more majority carriers will be able to cross the junction, and the forward current increases exponentially with the forward voltage V_D. The diode is now in a conducting state, or the diode is in the ON state.

• Case 3: If V_D = V₀

The effect of the barrier is nullified, i.e., the barrier will no longer oppose any majority carriers crossing the junction. Both the majority and minority carriers will be able to cross the junction. Hence, the forward current is small, or it just starts to flow into the diode.

Forward Bias is a term commonly used in semiconductor electronics, particularly concerning diodes and transistors. A diode is considered to be in forward bias when its p-side is connected to the positive side of a power supply and its n-side to the negative side. In the case of an NPN transistor, the base-emitter junction is forward-biased, which means the base is positive relative to the emitter. Conversely, for a PNP transistor, the base is negative relative to the emitter.

In this article, we will discuss all Forward Biases including Forward Bias of PN junctions and transistors.