Intraband absorption and Stark effect in silicon nanocrystals

Abstract

Received 3 May 2005; published 27 October 2005A theoretical investigation of the combined effect of confinement geometry, valley degeneracy, crystallo-graphic orientations, and anisotropy of the effective mass on the intraband absorption of the conduction bandof Si nanocrystals is presented. We show that the coupling between the nanocrystal shape and arbitraryorientations of the crystalline Si core plays a dramatic role in the intraband optical properties through inter-esting changes in the electronic structure and intra- and inter-valley degeneracy. Different orientations of thecrystalline Si also affect the shape and orientation of the orbital wave functions, thereby modifying transitionrules and fine structure of the intraband absorption. The anisotropy of the effective mass is also responsible forthe emergence of absorption peaks that are not present in isotropic nanocrystals. Additional intraband transi-tions are also induced by changes in the nanocrystal shape with respect to spherical dots. Moreover, thequantum confined Stark effect blueshifts the absorption peaks and induces the appearance of peak structures asa consequence of the relaxation of selection rules caused by the displacement of the wave functions in responseto external electric fields. This effect was found to be only appreciable in large nanocrystals.DOI: 10.1103/PhysRevB.72.155438 PACS number s : 73.21.La, 73.22.Dj, 78.67.Bf, 78.20.Bh