Reverse biased | Working of PN Junction.
Reverse biased
A pn junction is said to be reverse biased if p type semiconductor is connected to the negative terminal and n type semiconductor to the positive terminal of the external battery.
The majority carriers, holes, are attracted to the negative voltage terminal, and electrons are attracted to the positive voltage terminal, both displaced away from the junction.As a result the depletion region increases, barrier height is increased as shown in fig. If the applied potential across the junction is V, the modified potential will be barrier potential and applied potential. Due to this increased potential barrier the majority carriers (holes in p region and free electrons in n region) are unable to cross the barrier potential. Since the junction offers very high resistance, so the flow of current is almost stopped. But the minority carriers i.e free electrons of the p region have a tendency to flow towards the positively biased n region, while holes of n region have the tendency to move towards the negatively biased p region.
The current due to the flow of minority carriers remains the same whether the battery voltage is low or high. Hence this current is called reverse saturation current. But if the reverse bias is made too high, the current through the pn junction increases abruptly. The voltage at which this phenomenon occurs is called breakdown voltage. At this voltage, the crystal structure breaks down.
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