Prediction of charge separation in GaAs/AlAs cylindrical Russian Doll nanostructures

(February 1, 2008) Recent advances in nanotechnology permit fabrication of complex nanostructures with special electronic and optical properties reflecting dimensional confinement on a nanometer scale, e.g. multiple quantum wells and core-shell structures.4–7 The essential building blocks of such structures are alternating layers of different semiconducting materials, acting as “wells” and “barriers”, and controlling the confinement energies and, thus the localization of charge carriers. Electrons and holes are confined in wells and repelled from barriers much like in “a particle in a box”: as the well narrows, the kinetic energy of the confined particle rises. The materials comprising the wells and barriers are usually flat, two-dimensional semiconductor films, stacked like a deck of cards to produce “multiple quantum wells” or “superlattices”. In this case, wave functions of the conduction band minimum (CBM) and valence band maximum (VBM) at the Brillouin zone center, are localized on the widest wells, having the lowest confinement energy. We have contrasted the quantum confinement of (i) multiple quantum wells of flat GaAs and AlAs layers, i.e. (GaAs)m/(AlAs)n/(GaAs)p/(AlAs)q, with (ii) “cylindrical Russian Dolls” – an equivalent sequence of wells and barriers arranged as concentric wires (Fig. 1). Using a pseudopotential plane-wave calculation, we identified theoretically a set of numbers (m, n, p and q) such that charge separation can exist in “cylindrical Russian Dolls”: the CBM is localized in the inner GaAs layer, while the VBM is localized in the outer GaAs layer. In contrast, the band edge states of linear multiple quantum wells with