Zero-bias equilibrium, Electrical Engineering

Assignment Help:

Zero-Bias Equilibrium

In a p-n junction, with no an external applied voltage, an equilibrium condition is arrived at in which a potential variation is formed across the junction. This potential difference is termed as built-in potential Vbi.

Later than joining p-type and n-type semiconductors, electrons that are near the p-n interface tend to diffuse into the p region. As electrons diffuse, they depart positively charged ions (donors) in the n region. Likewise, holes near the p-n interface start to diffuse into the n-type region leaving fixed ions (acceptors) along with negative charge. The regions near the p-n interfaces lose their neutrality and become charged, creating the space charge region or depletion layer.

616_Zero-Bias Equilibrium 1.png

Figure: A p-n junction in thermal equilibrium with zero bias voltage applied. Electrons and holes concentration are reported correspondingly with blue and red colored lines. Gray regions are charge neutral. Light red zone is charged positively. Light blue zone is charged negatively. The electric field is displayed on the bottom, the electrostatic force on electrons and holes and the direction in which the diffusion tends to move electrons and holes.

The electric field that is created by the space charge region opposes the diffusion procedure for both electrons and holes. There are 2 concurrent phenomena: the diffusion process which tends to produce more space charge and the electric field produced by the space charge which tends to counteract the diffusaion. The carrier concentration profile at equilibrium is displayed in figure with blue and red colored lines. As well shown are the two counterbalancing phenomena which establish equilibrium.

1054_Zero-Bias Equilibrium 2.png

Figure:  A p-n junction in thermal equilibrium with zero bias voltage applied. Within the junction, plots for the charge density, the electric field and the voltage are reported.

The space charge region is a zone with a net charge that is provided by the fixed ions (donors or acceptors) which have been left uncovered via majority carrier diffusion. While equilibrium is arrived at, the charge density is approximated through the displayed step function. Actually, the region is totally depleted of majority carriers (leaving a charge density equal to the net doping level), and the edge among the space charge region and the neutral region is quite sharp. The space charge region has similar charge on both sides of the p-n interfaces, so it extends farther on the less doped side.


Related Discussions:- Zero-bias equilibrium

Transformer onnection, what is difference between scot and delta connection...

what is difference between scot and delta connection.

Pinch off voltage, Pinch off Voltage: The current in N-JFET because of...

Pinch off Voltage: The current in N-JFET because of a small voltage V DS  is described by: I DSS = (2a) W/L (qN d μ n V DS ) In which 2a  = channel thickness

Fulfilled to sustain the oscillations, Q. What are the conditions required ...

Q. What are the conditions required to be fulfilled to sustain the oscillations? The conditions required to be fulfilled to sustain the oscillations are: 1. The loop gain mu

State the principle of operation of a capacitor, a. Describe why a three-ph...

a. Describe why a three-phase induction motor rotates always with a speed less than the synchronous speed. b. State the principle of operation of a capacitor start single-phase

Microprocessors, Microprocessors: We have learnt 8085 family of microp...

Microprocessors: We have learnt 8085 family of microprocessors. Initially, we understand basic components of a computer, 8085 microprocessor architecture and assembly language

Two-level system - princeton, Conceive a system composed of a very large nu...

Conceive a system composed of a very large number N of distinguishable atoms at rest and mutually noninteracting, each of which has only two (nondegenerate) energy levels:0,ε>0 Let

Define smoothing the output, Define Smoothing the Output? The output of...

Define Smoothing the Output? The output of a DAC is stepped, such as the analog waveforms which were sampled and held. This stepped, or staircase effect is a distortion, and it

Torque required to turn a self excited generator, Work must be done against...

Work must be done against the electromagnetic torque in order to generate the voltage (and current) supplied to the electrical load connected to the generator. Therefore energy con

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd