Faculty of Physics - University of Bucharest

UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2007 Meeting

Section: Solid State Physics and Materials Science

Title:

Influence of the dielectric effects on the localized electronic states in porous silicon wires

Authors:

Ana Ioanid

Affiliation:

Faculty of Physics, University of Bucharest

E-mail

aioanid@solid.fizica.unibuc.ro

Keywords:

porous silicon,embedding medium, quantum confinement,shift of luminescence.

Abstract:

In porous silicon, in presence of localized states (e.g., ionized impurities), the energy levels are dramatically affected by the dielectric properties of the embedding medium. In the case of an embedding medium of low-dielectric constant (vacuum, oxides,…), the quantum confinement and polarization charge effects tend to increase the binding energies on the localized states by screening its long-range Coulomb potential. In the case of an embedding medium with a large low-frequency dielectric constant, such as a polar solvent, it is found that the deep impurity states still exist, but the trapping probability of an opposite charge into them is reduced due to slow dielectric relaxation effects. These effects gives a plausible explanation for the predominance of the green luminescence and the observation of large free-carrier densities in wet porous silicon. The decrease of the dielectric constant of the embedding medium favours an increasing trapping probability of the photocarrieres into localized states and finally , a red shift of the green luminescence.