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Depletion Layer and Energy barrier

Explain the formation of depletion region and potential barrier in a pn junction diode.

Asked  Sunder Bisht

Answer:

The depletion region (also called depletion layer, depletion zone, junction region, space charge region or space charge layer) is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have been diffused away, or have been forced away by an electric field. The only elements left in the depletion region are ionized donor or acceptor impurities.

semiconductor pn junction

When the N-type semiconductor and P-type semiconductor materials are first joined together, a very large density gradient exists between both sides of the PN junction. The result is that some of the free electrons from the donor impurity atoms begin to migrate across this newly formed junction to fill up the holes in the P-type material producing negative ions.

A depletion region forms instantaneously across a p–n junction. It is most easily described when the junction is in thermal equilibrium or in a steady state: in both of these cases the properties of the system do not vary in time; they have been called dynamic equilibrium.

Electrons and holes diffuse into regions with lower concentrations of electrons and holes, much as ink diffuses into water until it is uniformly distributed. By definition, N-type semiconductor has an excess of free electrons compared to the P-type region, and P-type has an excess of holes compared to the N-type region. Therefore, when N-doped and P-doped pieces of semiconductor are placed together to form a junction, electrons migrate into the P-side and holes migrate into the N-side. Departure of an electron from the N-side to the P-side leaves a positive donor ion behind on the N-side, and likewise the hole leaves a negative acceptor ion on the P-side.

Following transfer, the diffused electrons come into contact with holes on the P-side and are eliminated by recombination. Likewise for the diffused holes on the N-side. The net result is the diffused electrons and holes are gone, leaving behind the charged ions adjacent to the interface in a region with no mobile carriers (called the depletion region). The uncompensated ions are positive on the N side and negative on the P side. This creates an electric field that provides a force opposing the continued exchange of charge carriers. When the electric field is sufficient to arrest further transfer of holes and electrons, the depletion region has reached its equilibrium dimensions. Integrating the electric field across the depletion region determines what is called the built-in voltage (also called the junction voltage or barrier voltage or contact potential).

(Ref: https://en.wikipedia.org/wiki/Depletion_region)

 

 

 

Electrons in metals at 0K

We know that at 0K all the electrons will be in valence shell of semiconductors………..is it the case with even metals?

-Velpuri asked.

Please refer to the following links for details

1. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi2.html

2. http://www.physics.umd.edu/courses/Phys798S/anlage/Phys798SAnlageSpring06/Free_Electron_Model.pdf

3. http://www.cmmp.ucl.ac.uk/~ikr/3225/Section%206.pdf

4. http://www2.phy.ilstu.edu/~marx/ph355/Kittel_Solid%20State%20Physics/c06.pdf

HOW TO PROVE THAT A NAND GATE IS A UNIVERSAL GATE??

NAND GATE and NOR GATE can be used as universal gates because all the basic logic gates can be realized using NAND or NOR alone as detailed below.

Realization of Basic logic Gates using NAND

Realization of Basic logic Gates using NAND

 

Realization of Basic logic Gates using NOR

Realization of Basic Logic Gates using NOR gate

 

Read more at http://www.ccse.kfupm.edu.sa/~amin/eCOE200/Lesson2_6.pdf

A question from semiconductors

Draw the circuit diagram used to study the characteristics of an NPN transistor in common emitter configuration.Give the shape of these characteristics & use them to define the
(i)input resistance &
(ii)the current amplification factor of the
given transistor.

 

Asked Vikas

Transformers

A hypothetical ideal transformer considered as...

A hypothetical ideal transformer considered as a circuit element, consisting of N P turns in the primary winding, and N S in the secondary. Electrical power supplied to the primary circuit is delivered to the load in secondary circuit by means of mutual induction. The time-varying magnetic flux in the core generates an electromagnetic force over each of the windings. The voltage and current relationships are shown below. (Photo credit: Wikipedia)

Please explain what is transformer and tell what is the reason behind the working of transformer that it reduces potenial when current is high and increases potential when current is low?

Explain widely and deeply with concepts.

Answer:

Transformer is a device based on mutual inductance and is used to change the voltage of alternating (or varying) current. There are two types of transformers – stepup and stepdown.

A step-up transformer increases the voltage as the step-down transformer decreases the ac voltage.

When a transformer changes the alternating voltage, it is not adding any power, it only transforms the voltage.

As power is the product of voltage and current, as voltage increases, the current decreases. (and vice versa)

The following links will help you understand transformers in great detail.





HOW DOES A REMOTE (CONTROLLER) WORK

Explain me how infrared are detected by televison sets which are sent by remote and how does the channel change?

Asked Rahul

A remote is an electronic device which sends infra red signals whenever you press a buton on the remote controller. Each button press is translated into a sequence of 0s and 1s and accordingly the IR signal is produced.

You might have noticed the LED at the front end of the remote. The IR light cannot be seen through naked eye, but it can be seen through a mobile camera because the camera is sensitive to IR light too.
The infrared sensor of your TV receives the signal and decodes it into digital signal and sends it to the microprocessor. Appropriate actions (changing the channel, increasing the volume etc) are triggered by the microprocessor. For each operation there is a separate didital code (produced by different buttons on the remote)

Solution to HC Verma Problem

“Referring to HC Verma Part 2, chapter 29, Electric field and potential, Q 69
I think that Force is inversely proportional to square of the distance between the charged particles, so acceleration is not constant and hence
v*v  =  u*u  + 2*a*s   is not valid in this case.
How is proceed with this question ?” Satyam asked

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