Intrinsic defect band models

This situation can be expressed in terms of the band model as shown in Fig. 1.24. Stoichiometric NiO is an intrinsic semiconductor, having an energy gap of Eq (=Eq—E ). Non-stoichiometric Nij O, which has metal vacancies or electronic defects, has an acceptor level A between the valence... 

The electronic band structure of a neutral polyacetylene is characterized by an empty band gap, like in other intrinsic semiconductors. Defect sites (solitons, polarons, bipolarons) can be regarded as electronic states within the band gap. The conduction in low-doped poly acetylene is attributed mainly to the transport of solitons within and between chains, as described by the intersoliton-hopping model (IHM) . Polarons and bipolarons are important charge carriers at higher doping levels and with polymers other than polyacetylene. 

In summary, the origins of photoluminescence mainly stem from the matrix-, native-, and doping-induced defects. Based on the experimental characterization, the first-principles calculation gives an acceptable model to explain the luminescence mechanism. For intrinsic emission, different DFT methods are applied to modify the band gap to meet the experimental value. The intrinsic Imninescence... 

They found good agreement between experiment and theory for surface-modified CdSe nanocrystallites. This agreement suggests that the band edge luminescence of CdSe QDs can be quantitatively understood using an intrinsic exciton model and that the role of the surface in the optical properties of the QDs lies in its defects which create deep red radiative and nonra-diative pathways for recombination of the electron and hole upon photoexcitation of the nanocrystallite [6]. 

The simplest model of the material which can account for the major performance features of these photoconductors is the following. The semiconductor is assumed -type with riQ = N — and P p, although one could use the same model for p-type material by exchanging ns and p s. This is an extrinsic semiconductor while also an intrinsic photoconductor. The material contains centers which can trap holes (minority carriers) from the valence band generally The traps may be defects in the bulk crystal, surface... 

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