The higher excited electronic states and spin–orbit splitting of the valence band in three-dimensional assemblies of close-packed ZnSe and CdSe quantum dots in thin film form

Abstract

Optical properties of as-deposited and annealed thin films composed of three-dimensional arrays of sphalerite-type ZnSe and CdSe quantum dots (QDs), synthesized by chemical deposition, were investigated. Neglecting the S– D mixing of hole states, the lowest “band to band” transitions in very small nanoclusters and in bulk-like clusters may be assigned as 1 S→1 S and 1 S Δ →1 S, and are split by spin–orbit (SO) splitting energy of the bulk material— Δ. The splitting energy between these transitions was found to be insensitive to QD size variations, which could be explained assuming that 1 S hole states arising from valence band Γ 7 and Γ 8 components do not mix with higher angular momentum states and shift together to higher energies coupled via the isotropic hole mass. This implies significant difference between the SO splitting energies in the two semiconductors. Accounting for S– D mixing of hole states, the observed transitions may be attributed to the fundamental ground state—(1 S 3/2, 1 S e) and the ground state—(1 S 1/2, 1 S e) ones. The observed “splittings” thus do not correspond exactly to SO splitting energy in both semiconductors, but are complex functions of it, as exact position of each hole energy level depends, besides on Δ, also on other material-characteristic parameters.