Excitons and excitonic fine structures in Si nanowires: Prediction of an electronic state crossover with diameter changes

Electronic and optical properties of semiconductor nanostructures

“…It has been demonstrated by large scale DFT calculations 294 that the internal field even in a polar quasi-one-dimensional nanorod (NR) does not depend strongly on the spontaneous polarization of the underlying lattice.This type of surface passivation has been practiced successfully previously for this material system, 145,240,269 and very recently in Si NWs. 293 It should be noted here that the nature of the surface passivation and morphology may play an important role in the determination of the electronic and optical properties of semiconductor NWs, especially with smaller sizes. However, in our calculations, the emphasis is put on the size effects rather than the surface effects.…”

“…The Coulomb and exchange integrals are screened by the position-dependent and size-dependent screening function proposed by Resta (see Section 9.5.2 of Chapter 9), which gives a physically smooth transition from short range (unscreened) to long range (screened). 236,293 An important issue in the calculation of excitonic properties in nanostructures is the treatment of correlations. Our CI treatment exhibits a poor scaling, which limits the number of states that we are able to include in the expansion.…”

“…The surface dangling bonds are passivated by employing a high band gap artificial material, as successfully practised previously. 145,240,269,292,293 The geometry of our smallest QD structure (e.g., with radius R = 1 nm, unpassivated) is displayed in Fig. 12.2(a) and the…”

“…The manybody excitonic properties are calculated via configuration interaction (CI) approach 263 and the excitonic wave functions are expanded in terms of single-substitution Slater determinants constructed from the single-particle wave functions of electrons and holes (see Section 9.5 of Chapter 9). The Coulomb and exchange integrals are screened by the position-dependent and size-dependent screening function proposed by Resta, 248 which gives a smooth transition from short range (unscreened) to long range (screened) 263,293 (see Subsection 9.5.2 of Chapter 9). We include in the CI treatment 4 states from the conduction band and 10 states from the valence band.…”

“…236 This method has been shown to describe very well the excitonic properties in wurtzite CdSe quantum dots (QDs), 255 and very recently in ZnO QDs 145,292 and Si NWs. 293 In the following section, we present the computational details.…”