Physics for Information Science: Unit IV: Optical Properties of Materials
Optical Absorption in Semi-Conductors
When light is allowed to fall over semi-conductors the electrons in the valence band absorb the energy from light and it moves from valence band to conduction band.
OPTICAL
ABSORPTION IN SEMI-CONDUCTORS
When
light is allowed to fall over semi-conductors the electrons in the valence band
absorb the energy from light and it moves from valence band to conduction band.
The transition depends purely on the energy band gap between the valence band
and conduction band. The energy band gap of a semiconductor is given by
From
this relation we can say that the absorption edge (λ) is inversely proportional
to the energy band gap, (i.e.) the materials having small energy band gap (Eg)
will absorb the lower wavelength and allow the higher wavelength of light.
Explanation:
When light is allowed to fall on a zinc selenium crystal which has the band gap
Eg = 4800Å, corresponding to bluish green wavelength, then it
absorbs the bluish green light and emits the wavelength of light greater than
bluish green (i.e.) yellow light, which is at longer wavelength side.
The
wavelength that is absorbed with respect to the energy band gap of the material
is called Absorption Edge.
Hence
we can say that the materials having low energy band gap will absorb lower
wavelength corresponding to the Eg and allow the wavelength of
higher range.
Physics for Information Science: Unit IV: Optical Properties of Materials : Tag: : - Optical Absorption in Semi-Conductors
Physics for Information Science: Unit IV: Optical Properties of Materials
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