Radiative Recombination in Semiconductors

8/11/2019 Radiative Recombination in Semiconductors

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Radiative

Recombination inSemiconductorsStudy of Radiation spectra and its applications

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What is Recombination? The process in which when an electron falls from the

conduction band into a hole in the valence band, they

annihilate each other with the release of photons/phonons-

Electroluminescence.

Reverse process of e-h pair generation

Two kinds of recombination

Radiative Recombination (with the release of photon)

Non-Radiative Recombination (with phonons/lattice vibration)

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Radiative Recombination

Optical processes associated with radiative transitions

Spontaneous emission

Absorption or Gain

Stimulated emission

Non-Radiative Recombination

Processes associated with non-radiative transitions

Auger Recombination

Surface Recombination

Recombination at defects 4


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Radiative Recombination

The overall recombination rate in germanium and silicon is

governed by non-radiative transitions.

Investigations of the spectra of recombination radiation, first

detected by O. V. Losev in silicon carbide yielded information-

band structure

energy levels of impurities and defects

crystal lattice vibrations of germanium, silicon, and other

semiconductors

By the application of the principle of detailed balance, thespectral distribution of the rate of photon generation for the

photon-radiative recombination of electrons and holes in

germanium was determined[2]5


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Principle of Detailed Balance[3]

The Law of Entire Equilibrium [4] or The Principle of

Microscopic Reversibility [5] or The Hypothesis of the

Unit Mechanism [6] or The Principle of Detailed

Balancing [7]

A sample is said to be in thermodynamic equilibrium when, the temperature of the sample is the same as that of its

environment

there is no change of temperature in time

there are no external forces acting on the sample, for instance

an applied voltage or excess illumination from a light source.

If a sample is in thermal equilibrium, then all microscopic

processes in the sample are exactly compensated by their

respective inverse process.6


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Conclusions from the study of

radiation spectra

Based on the Theory of Detailed Balancing, interband

radiative recombination should be more likely in

semiconductors with a narrow forbidden band, than in

germanium or silicon[2]

In some cases, this type of recombination determines the

overall lifetime of minority carriers.

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Radiative recombination lifetimes[8]

This table shows that for substances with narrow forbidden

band, the max. observed lifetimes are much lower => higherprobability of radiative recombination

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Excitation and Investigation of

Recombination spectra Experimental methods to study recombination radiation

spectra

by excitation with short wavelengths (more convenient

method to study intrinsic recombination)

by the injection of carriers by passing a current through a p-njunction in the forward direction

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Experimental set up

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References [1]V. S. Vavilov, Effects of radiation on Semiconductors, Springer

Science+Business Media, LLC,1965,Ch.4,pp. 112-119 [2]W. Van Roosbroeck and W. Shockley, Photon Radiative

recombination of electrons and holes in Germanium, Phys. Rev. 94,

6,pp. 1558-1560,Jun.,1954)

[3] Thomas Kirchartz, Generalized detailed balance theory of solar

cells

[4] G. N. Lewis, Proc. Nat. Acad. Sci. 11, 179 (1925).

[5] R. C. Tolman, Proc. Nat. Acad. Sci. 11, 436 (1925).

[6] O. E. Richardson, Proc. Roy. Soc. Lon. 36, 392 (1924).

[7] E. O. Lawrence, Phys. Rev. 27, 555 (1926). [8] E. Burstein and P. H. Egli, "Physics of semiconductors" (a

review), in collection: Physics of Semiconductors [Russian

translation], 1957.12

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Radiative Recombination in Semiconductors