Physics for Electrical Engineering: Unit IV: Optical Properties of Materials
Charge injection and radiative recombination
Optical Properties of Materials
Electrons and holes can be injected into the conduction and valence band in a number of way. The light incident on the material and the absorption of photons creates electron-hole pairs.
CHARGE INJECTION AND RADIATIVE RECOMBINATION
Electrons
and holes can be injected into the conduction and valence band in a number of
way. The light incident on the material and the absorption of photons creates
electron-hole pairs.
We
also use an external battery bias in a p-n diode also inject electrons and
holes.
The
electrons and holes will recombine with each other and the electron in the
conduction band will return to the valence band.
This
recombination process can be made in two processes. They are (i) radiative
processes and (ii) non-radiative processes.
In
the radiative process the e-h pair recombines and a photon is emitted. The is
the inverse of the photon absorption process.
Electron-hole
pairs can also recombine without emitting light. Instead, they may emit (i)
heat or (ii) a photon or (iii) a long-wavelength photon together with a phonon.
Such processes are non-radiative processes.
As
the electrons and holes are "pumped" into the semiconductor they
re-combine through the process of spontaneous emission. This process does not
require photons to be present for the photon emission process to occur.
The
spontaneous recombination rate is quite important for both electronic and
optoelectronic devices.
Types of carrier Injections
(i)
Minority Carrier Injection
If
n >> p and the sample is heavily doped n-type, recombination rate is
proportional to hole density.
Thus
the recombination rate is proportional to the minority carrier density (holes
in the case).
(ii)
Strong Injection
This
case is important when a high density of both electrons and holes is injected.
The
rate of recombination proportional to majority charge carrier.
(iii)
Weak Injection
In
this case, the rate of recombination is very low.
(iv)
At low injection, the electrons have a low probability
to find a hole with which to recombine.
Physics for Electrical Engineering: Unit IV: Optical Properties of Materials : Tag: : Optical Properties of Materials - Charge injection and radiative recombination
Physics for Electrical Engineering: Unit IV: Optical Properties of Materials
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Physics for Electrical Engineering
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