Why does the pn junction have unilateral conductivity?

If an external voltage is applied to the semiconductor layers so that the electric field created by it is directed opposite to the field existing in the junction, then the dynamic equilibrium is violated, and the diffusion current prevails over the drift current, rapidly increasing with increasing voltage. Such a voltage connection to the p – n-junction is called forward bias (a positive potential is applied to the p-type region with respect to the n-type region).
If an external voltage is applied so that the field created by it is in the same direction as the field in the junction, this will only lead to an increase in the thickness of the space charge layers. The diffusion current will decrease so much that a small drift current will prevail. This connection of voltage to the p – n – junction is called reverse bias (or locking bias).

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