The PN junction is one of the basic building block of integrated circuits. Such a junction can be formed by selective diffusion or ion implantation of N-type dopants into a P-type(or P-type into N-type) semiconductor sample.
The Fermi level in a P-type semiconductor lies close to the valence band edge, while in an N-type semiconductor it lies close to the conduction band edge. this means that P-region has a higher concentration of holes, while N-region has higher concentration of electrons.
When P-region and N-region are brought in close contact, this large concentration gradient at the junction causes diffusion of carriers.
Holes diffuse from P-region to N-region, electrons diffuse from N to P-region. This process results in some uncompensated donor ions (ND+) in N-region and uncompensated acceptor ions (NA-) in P-region near the junction.
Consequently, a negative space charge builds in the P-region and a positive space charge in N-region.
This creates a built-in electric field directed from N-region to P-region which gives rise to a drift current. The direction of drift current will be opposite to that of the diffusion current.
An equilibrium condition is reached where there is no net transport of carriers, as the diffusion component is balanced by an equal and opposite drift component of current.
Far from the junction, electron and hole concentration on both sides remain unaffected. Hence the position of valence band and conduction band with respect to Fermi level also remains the same as they were before the junction was formed.
In the space charge region, the conduction and valence band edges bend accounting for the presence of an electric field. The N-region is at higher electrostatic potential than the P-region. This difference is given by qVbi, where Vbi is contact potential or built-in potential.
The electric field in the bulk quasi-neutral region is zero.
Φp and Φn are defined as the electrostatic potential of P-type and N-type quasi-neutral region with respect to the fermi level.
Mathematically expressed as,
The total electrostatic potential difference between the P-side and N-side regions at thermal equilibrium is equal to the built in potential. i.e.
The Fermi level in a P-type semiconductor lies close to the valence band edge, while in an N-type semiconductor it lies close to the conduction band edge. this means that P-region has a higher concentration of holes, while N-region has higher concentration of electrons.
When P-region and N-region are brought in close contact, this large concentration gradient at the junction causes diffusion of carriers.
Holes diffuse from P-region to N-region, electrons diffuse from N to P-region. This process results in some uncompensated donor ions (ND+) in N-region and uncompensated acceptor ions (NA-) in P-region near the junction.
Consequently, a negative space charge builds in the P-region and a positive space charge in N-region.
This creates a built-in electric field directed from N-region to P-region which gives rise to a drift current. The direction of drift current will be opposite to that of the diffusion current.
An equilibrium condition is reached where there is no net transport of carriers, as the diffusion component is balanced by an equal and opposite drift component of current.
Far from the junction, electron and hole concentration on both sides remain unaffected. Hence the position of valence band and conduction band with respect to Fermi level also remains the same as they were before the junction was formed.
In the space charge region, the conduction and valence band edges bend accounting for the presence of an electric field. The N-region is at higher electrostatic potential than the P-region. This difference is given by qVbi, where Vbi is contact potential or built-in potential.
The electric field in the bulk quasi-neutral region is zero.
Φp and Φn are defined as the electrostatic potential of P-type and N-type quasi-neutral region with respect to the fermi level.
Mathematically expressed as,
Vbi= Φn -Φp
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