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 A12-V, 115-Ah automobile storage battery is used to light a 6-W bulb. Assuming the battery to be a constant-voltage source, find how long the bulb can be lighted before the batte

Q. What do you mean by diversifiability of total risk? Traditional finance theory assets that the rate of return on risk assets depends on the size of business risk, financial

Responses to Exponential Excitations Let us consider Aest as a typical exponential excitation in which A is a constant and s is a complex- frequency variablewith a dimension of

A 300 km, 3-phase, 50Hz transmission line has spacing as shown in Figure. Each phase of the line consists of a bundle of three conductors. (a) Find the total per-phase inductanc

Q. What do you mean by Phase Sequence? It is standard practice in the United States to designate the phase A-B-C such that under balanced conditions the voltage and current in

Q. How oscillations start up in an oscillator?  The noise voltage produced due to the random motion of electrons in resistors or in active devices provides the starting voltage

What is meant by doping? Doping: Semiconductors in its extremely pure form are termed as intrinsic semiconductor such intrinsic semiconductor to which several suitable impur

How DRAM's are different from SRAM's? Why DRAMs are said to use address multiplexing? Ans Dynamic RAM (DRAM) is basically the same as SRAM except that it recollects data f