A p–n junction is a boundary or interface between two types of semiconductor materials, p-type The regions near the p–n interface lose their neutrality and most of their mobile carriers, forming the space charge region or depletion layer (see  ‎Properties · ‎Governing equations · ‎Non-rectifying junctions · ‎Manufacture. Depletion Region. When a p-n junction is formed, some of the free electrons in the n-region diffuse across the junction and combine with holes to form negative ions. In so doing they leave behind positive ions at the donor impurity sites. Formation of a P-n junction. P-n junctions are formed by joining n-type and p-type semiconductor materials, as shown below. Since the n-type region has a high electron concentration and the p-type a high hole concentration, electrons diffuse from the n-type side to the p-type side.


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The regions near the p—n interface lose their neutrality and most of their mobile carriers, forming the space charge region or depletion layer see figure A.


A p—n junction in thermal equilibrium with zero-bias voltage applied. Electron pn junction formation hole concentration are reported with blue and red lines, respectively. Gray regions are charge-neutral.

Light-red zone is positively charged.

PN Junction formation and How it works

Light-blue zone is negatively charged. The electric field is shown on the bottom, the electrostatic force on electrons and holes and the direction in which the diffusion tends to move electrons and holes.

The log concentration curves should pn junction formation be smoother with slope varying with field strength.

The electric field created by the space charge region opposes the diffusion process for both electrons and holes. There are pn junction formation concurrent phenomena: The carrier concentration profile at equilibrium is shown in figure A with blue pn junction formation red lines.

Let us consider a thin p-type silicon semiconductor sheet. If we add a small amount of pentavalent impurity to this, a part of the p-type Si will get converted to n-type silicon.

P-N Junction

This sheet will now contain both p-type region pn junction formation n-type region and a junction between these two regions. The processes that follow after the formation of a p-n junction are of two types — diffusion and drift.

Minority carriers which reach the edge of the diffusion region are swept across it by the electric field in the depletion region. This current is called the drift current.

P-N Junctions

In equilibrium the drift current is limited by the pn junction formation of minority carriers which are thermally generated within a diffusion length of the junction. In equilibrium, the net current from the device is zero.

The electron drift current and the electron diffusion current exactly pn junction formation out if they did not there would be a net buildup of electrons on either one side or the other of the device.

Similarly, the hole drift current and the hole diffusion current also balance each other out. Bias of p—n Junctions Diodes under Forward Bias Forward bias refers to the application of voltage across the device such pn junction formation the electric field at the junction is reduced.

By applying a positive voltage to the p-type material and a negative voltage to the n-type material, an electric field with opposite direction to that in the depletion region pn junction formation applied across the device.


Since the resistivity of the depletion region is much higher than that in pn junction formation remainder of the device due to the limited number of carriers pn junction formation the depletion regionnearly all of the applied electric field is dropped across the depletion region.

The net electric field is the difference between the existing field in the depletion region and the applied field for realistic devices, the built-in field is always larger than the applied fieldthus reducing the net electric field in the depletion region.

  • Formation of a PN-Junction | PVEducation
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This results in the formation of an electric field directed from positive charge to negative charge. If you observe carefully, you can easily see that drift current is opposite in direction to the diffusion current. Image Source The formation of PN Pn junction formation As we have understood the concepts of diffusion, depletion pn junction formation and drift, lets find out how the formation of PN junction gets completed.

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