Direct and indirect semiconductors, Electrical Engineering

Assignment Help:

Direct and Indirect Semiconductors

1) In a common quantitative calculation of band structures, the wave function of a single electron traveling by a perfectly periodic lattice is assumed to be in the type of a plane wave moving in the x-direction (say) with propagation constant k, as well called a wave vector.

2) In quantum mechanics, the electron momentum can be provided by p= hk.

3) The wave function that is space dependent for the electron is ΨK (X) = U (Kx,x) ejK,x  in which the function U(Kx,x) modulates the wave function as per to the periodicity of the lattice.

4) Allowed values of energy, where as plotted as a function of k, gives the E-k diagram.

5) As the periodicity of most lattices is different in several directions, the E-k diagram is a complex surface that is to be visualized in three dimensions.

6) Direct band gap semiconductor: the minima of the conduction band and the maxima of the valence band take place at the same value of k => an electron creating the smallest energy transition from the conduction band to the valence band can do so with no a change in k (and, the momentum).

1968_Direct and Indirect Semiconductors.png

Figure:  Direct and indirect transition of electrons from the conduction band to the valence band:  (a) direct - with accompanying photon emission, (b) indirect via defect level.  

7) Indirect band gap semiconductor: the minima of the conduction band and the maxima of the valence band take place for different values of k, so, the smallest energy transition for an electron needs a change in momentum.

8) Electron  that falling  from  conduction  band  to  an  empty  state  in  valence  band => recombination.

9) Recombination possibility for direct band gap semiconductors is much higher than as compared to that for indirect band gap semiconductors.

10) Direct band gap semiconductors give up the energy released throughout this transition (=Eg) in the form of light => employed for optoelectronic applications (e.g., LEDs and LASERs).

11) Recombination in indirect band gap semiconductors takes place by some defect states within the band gap, and the energy is released in the type of heat given to the lattice.

 


Related Discussions:- Direct and indirect semiconductors

Find the temperature coefficient of the resistance material, The field resi...

The field resistance of a dc machine is 50 ohm at 20 o C. The resistance increases to 55 ohm at 50 o C. Find the temperature coefficient of the resistance material. Ans: Sol

4gls - fourth generations languages, 4GLs (Fourth Generations Languages) ...

4GLs (Fourth Generations Languages) These  are called  non procedural  languages May be considered as  advanced HLL. Objects oriented programming  languages and language  with

Show a block diagram of a 4-bit, Q. Show a block diagram of a 4-bit, parall...

Q. Show a block diagram of a 4-bit, parallel-input shift-right register and briefly explain its operation.

Working of bootstrap sweep circuit, analysis and detail working of bootstra...

analysis and detail working of bootstrap sweep circuit

wind turbine, pls how can i stat up building wind turbin

pls how can i stat up building wind turbine

Dc motor control, how thyristor work in speed control??

how thyristor work in speed control??

Show process of power transmission and distribution, Q. Show Process of Pow...

Q. Show Process of Power transmission and distribution? The structure of a power system can be divided into generation (G), transmission, (T), and distribution (D) facilities,

Dc machine, why very high resistance wire is used is field windind and low ...

why very high resistance wire is used is field windind and low resistance wire is used in armature winding in DC shunt machine?

Main difference between a latch and a flip flop, Question: a) What is ...

Question: a) What is the main difference between a latch and a flip flop? b) Draw the logic diagram of an SR-latch using only NAND gates. c) A positive edge triggered

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