Table of Contents
When bias is strong enough that the depletion region becomes very thin, the diffusion component of the current (through the junction interface) greatly increases and the drift component decreases. In this case, the net current flows from the P-side to the N-side.
What happens in depletion region?
The depletion region is caused by the diffusion of charges. The holes and the electrons diffusing towards each other combine near the junction. In doing so positive and negative ions are formed. The pair of positive and negative ions at the junction forms the dipole.
How does current flow in PN junction diode?
In a forward-biased PN junction, once the barrier voltage is overcome, it conducts a current. The externally applied potential pushes majority carriers toward the junction where recombination takes place, allowing current flow.
What is present in depletion region?
Depletion region or depletion layer is a region in a P-N junction diode where no mobile charge carriers are present. Depletion layer acts like a barrier that opposes the flow of electrons from n-side and holes from p-side.
Why does an electric field generate in a depletion region?
Light travels in packets of energy called photons. The generation of electric current happens inside the depletion zone of the PN junction. The hole created by the dislodged electron is attracted to the negative charge of N-type material and migrates to the back electrical contact.
What is the purpose of depletion region?
The depletion region acts like a wall between p-type and n-type semiconductor and prevents further flow of free electrons and holes.
How does the depletion region behave?
In the depletion region, an electric field exists that quickly sweeps out electron-hole pairs that may be thermally generated and reduces the equilibrium concentration of the charge carriers to exceedingly low levels. This region, called the depletion layer, behaves as an insulator.
How does current flow in reverse bias?
In the reverse bias the voltage increases in the reverse direction across the p-n junction, but no current due to the majority carriers, only a minimal leakage current flows. But at a certain reverse voltage p-n junction breaks in conduction. It is only due to the minority carriers.
Why does current flow in forward bias?
A diode (PN junction) in an electrical circuit allows current to flow more easily in one direction than another. In a standard diode, forward biasing occurs when the voltage across a diode permits the natural flow of current, whereas reverse biasing denotes a voltage across the diode in the opposite direction.
What is the application of zener diode?
Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.
Why it is called depletion region?
The depletion region is so named because it is formed from a conducting region by removal of all free charge carriers, leaving none to carry a current.
How depletion layer is produced?
Depletion Region Details Filling a hole makes a negative ion and leaves behind a positive ion on the n-side. A space charge builds up, creating a depletion region which inhibits any further electron transfer unless it is helped by putting a forward bias on the junction.
What is the width of depletion region?
The physical width of the depletion region in a typical Si diode ranges from a fraction of a micrometer to tens of micrometers depending on device geometry, doping profile, and external bias.
How is depletion region calculated?
Depletion approximation: the electric field is confined to the junction region and there is no electric field in the quasi-neutral regions. No free carriers (n(x), p(x) = 0 ) in depletion region. 1 q d J n d x = ( U − G ) = 0 . This means that Jn is constant across the depletion region.
What is meant by Zener avalanche breakdown?
Valence electrons which break free under the influence of the applied electric field can be accelerated enough that they can knock loose other electrons and the subsequent collisions quickly become an avalanche. This process of sudden release of electrons is known as zener breakdown.
What is depletion region and potential barrier?
The depletion region is the space charge region on either side of the junction, which got depleted of free charges. The potential difference developed across the junction and opposes the diffusion of charge and brings equilibrium condition is known as the potential barrier.
Where does depletion region occur?
The word depletion in English refers to the decrease in the quantity of something. Similarly, in semiconductors, the depletion region is the layer where the flow of charges decreases. This region acts as the barrier that opposes the flow of electrons from the n-side to the p-side of the semiconductor diode.
Why there are no charge carriers in depletion region?
The region depleted of mobile charge carriers is called the depletion region. The depletion region has only positive ions and negative forms due to the diffusion of carriers across the junction of the pn diode.
What is the difference between a narrow and wide depletion region?
The breakdown voltage of a p-n junction diode is depends on the width of depletion region. The p-n junction diodes with wide depletion region have high breakdown voltage whereas the p-n junction diodes with narrow depletion region have low breakdown voltage.
What is the order of reverse current in a diode?
The very small current flows through the diode when the diode is in the reverse-biased state is called the reverse current of the diode. The reverse saturation current of a Germanium diode is of the orders of micro-amperes. While the reverse saturation current of a silicon diode is of the order of nano amperes.
What happens when depletion layer increases?
1. If the diode is reverse biased (a positive supply to the N side and negative to the P side), the depletion layer increases and only a small leakage current flows, due to the electrical field across the junction and residual thermal energy producing a small number of charge carriers.
What is a reverse bias?
Forward biasing means putting a voltage across a diode that allows current to flow easily, while reverse biasing means putting a voltage across a diode in the opposite direction. The voltage with reverse biasing doesn’t cause any appreciable current to flow. This is useful for changing AC current to DC current.
