Depletion Region and Built-in Potential A depletion region is an area in a PN junction diode that extends into the substrate beyond the depletion region. Thi...
A depletion region is an area in a PN junction diode that extends into the substrate beyond the depletion region. This region is formed by the lack of free charge carriers (electrons and holes) in the depletion region, which is caused by the applied voltage.
Properties:
The width of the depletion region is typically much smaller than the length and width of the entire junction.
It is heavily doped with either a majority or minority carrier, depending on the type of PN junction (p-type or n-type).
The built-in potential in the depletion region is an additional potential barrier that must be overcome for an external voltage to be applied across the junction.
Applications:
The depletion region and built-in potential are essential components in PN junction diodes used in various applications, including:
Switching devices: Used in digital circuits, where they control the flow of current.
Amplifiers: Used in amplifiers to amplify a small signal.
Sensors: Used in various sensors, such as photodiodes.
Oscillators: Used in oscillators, where they maintain a constant frequency.
Examples:
In an n-type PN junction diode, the depletion region is heavily doped with phosphorus atoms, creating a positive charge carrier region.
The built-in potential in this region is negative, meaning it is lower than the Fermi level in the substrate.
When a positive voltage is applied across the depletion region, it causes holes to be extracted from the p-type region, filling the space left by the holes.
This creates an electric field that pulls more holes into the p-type region, further widening the depletion region.
As the applied voltage increases, the depletion region width and built-in potential increase, limiting the current flow and controlling the overall behavior of the diode