Estimation of Absorption Coefficient, Oscillator Strength and Dielectric function of small Silicon Nanocrystallites
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Date
2009-06
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Addis Ababa University
Abstract
Even if bulk silicon is poor emitter of light, due to quantum size effect which leads to
an increase (the blue shift) of the band gap of the crystallites compared to bulk silicon,
silicon nanostructure (porous Silicon, quantum dots, quantum wells and nanoclusters
) exhibit strong photoluminescence at room temperature. Nanosilicon research is
gaining tremendous attention in recent years towards the possibility of photonic application.
In order to explain optical properties of nanoporous semiconductor i.e the variation
of absorption coefficient, dielectric constant and oscillator strength with size of
nanoporous semiconductor information about the density of states which depends on
the dimensionality of the system is very important. To do so, we obtain the density of
states for 3-D, 2-D and 1-D and the dipole matrix element with the help of Kane approximation
of momentum matrix element of direct band gap semiconductors. Using
the dipole matrix element together with the joint density of states between valence
and conduction band states we calculate the optical absorption coefficient, imaginary
part of the dielectric function as well as the oscillator strength near the band edge for
nanoporous semiconductor thus we find that the optical absorption coefficient and
the imaginary part of the dielectric function are explicit function of photon energy
and band gap energy but implicit function of the nanoporous semiconductors size
through band gap energy. Our results for these optical parameters are in conformity
with other observations
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Keywords
Estimation of Absorption Coefficient