A P-N junction diode is said to be forward biased when the positive terminal of a cell or battery is connected to the p-side of the junction and the negative terminal to the n side.
When diode is forward-biased the depletion region narrows and consequently, the potential barrier is lowered. This causes the majority charge carriers of each region to cross into the other region. The electrons travel from the n-side to the p-side and go to the positive terminal of the battery. The holes that travel from the p-side to the n-side combine with the electrons injected into the n-region from the negative terminal of the battery. This way the diode conducts when forward-biased.
Reverse-biased pn junction diode
A pn-junction diode is said to be reverse biased when the positive terminal of a cell or battery is connected to the n-side of the junction and the negative terminal to the p-side.
When reverse biased, the depletion region widens and the potential barrier is increased. The polarity of the battery extracts the majority charge carriers of each region. The holes in the p-region from the electrons injected into the p-region from the negative terminal of the battery. The electrons in the n-region go to the positive terminal of the battery. This way, the majority charge carrier concentration in each region decreases against the equilibrium values and the reverse biased junction diode has a high resistance. Thus, the diffusion current across the junction becomes zero. Thus, the diode does not conduct when reverse biased and is said to be in a quiescent or non-conducting state i.e., it acts as an open switch.
