Direct and indirect semiconductors, Electrical Engineering

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.


Posted Date: 1/11/2013 3:09:24 AM | Location : United States

Related Discussions:- Direct and indirect semiconductors, Assignment Help, Ask Question on Direct and indirect semiconductors, Get Answer, Expert's Help, Direct and indirect semiconductors Discussions

Write discussion on Direct and indirect semiconductors
Your posts are moderated
Related Questions
Q. Using K maps, simplify the following Boolean expressions: (a) F = A · ¯ B + A · B (b) F = A · C + C · D + B · C · D (c) F = A·B · ¯ C +B ·C +A·B ·D +B ·C ·D

Based upon the following inputs, propose the optimal course of action for this venture: Probability of success: 30%; probability of failure: 30%; base case probability: 40%

Q. When the quantum step size δv and the step size of f (t) are the same as in , the quantizer is said to have a gain of unity. If, on the other hand, the quantizer has a gain of K

Q. Differential amplifier to eliminate the common-mode voltage? The transducer in some cases may have a local ground that cannot be disconnected. In such a case, a separate gro

What is the difference between near call and far call? The PROC directive specifies the start of a procedure, should also be followed along with a NEAR or FAR. A NEAR procedure

A Class, "A" Amplifier is needed with the following specification: Collector Current = 5mA Needed offset voltage across RE= 2V Lowest input Frequency = 50Hz Use a BC108

What is the function of the time-base generator as used in an oscilloscope

A color television receiver is shown in Figure in block diagram form, indicating only the basic functions. The early part forms a straightforward superheterodyne receiver, except f

1. Suppose the California government sets aside a square patch of land that is 10 kilometers on each side and plans to use this land to generate electrical power with wind turbines

Error-Rate Control, Output-Rate Control, and Integral-Error (Reset) Control Let us consider a typical second-order servomechanism(containing two energy-storing elements) whose