When a pieces of p-type and pieces of N-type material are joined in such a manner that crystal structure remain continuous at the boundary ,then a PN junction is formed .This type of junction is known as PN junction diode.
The negative ions on the P-type S/C and positive ions on the N-type S/C are immobile .The majority hole carrier from the P-side diffuse into the N-side,and the majority electrons from N-region diffuse into P-region.Due to the above ,the electrons and hole at the junction region combine and disappear,i.e covalent bond are completed.As a result, a layer of negative ions on the P-side and the layer of positive ions on the N-side is formed at the junction.In this region,due to recombination of electrons and holes depletion of charge carrier occur to this region is called depletion region .The charge density on the two sides of the junction (due to ions layer )The uncompensated ions layer in the depletion region generate an electric field in this region .The electric field points from N-side to P-side .This electric field prevent s further diffusion of holes from P-region .It also prevent further diffusion of electrons from N-side to P-side .The barrier electric field gives rise to a different of potential from one side to other side .this is known as barrier potential. For Silicon PN junction the barrier potential is about 0.7 V whereas for Germanium PN junction is about 0.3 V. For hole the potential on the N-type S/C is higher .Holes can not cross the depletion region because of this barrier potential.
The negative ions on the P-type S/C and positive ions on the N-type S/C are immobile .The majority hole carrier from the P-side diffuse into the N-side,and the majority electrons from N-region diffuse into P-region.Due to the above ,the electrons and hole at the junction region combine and disappear,i.e covalent bond are completed.As a result, a layer of negative ions on the P-side and the layer of positive ions on the N-side is formed at the junction.In this region,due to recombination of electrons and holes depletion of charge carrier occur to this region is called depletion region .The charge density on the two sides of the junction (due to ions layer )The uncompensated ions layer in the depletion region generate an electric field in this region .The electric field points from N-side to P-side .This electric field prevent s further diffusion of holes from P-region .It also prevent further diffusion of electrons from N-side to P-side .The barrier electric field gives rise to a different of potential from one side to other side .this is known as barrier potential. For Silicon PN junction the barrier potential is about 0.7 V whereas for Germanium PN junction is about 0.3 V. For hole the potential on the N-type S/C is higher .Holes can not cross the depletion region because of this barrier potential.
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