Comparison of the k.p and the Direct Diagonalization Approaches for Describing the Electronic Structure of Quantum Dots

It is shown that the standard (decoupled) 6 X 6 k.p effective-mass approach for semiconductor quantum dots overestimates significantly the hole and electron confinement energies, and, for dots made of materials with small spin-orbit coupling (e.g. phosphides, sulphides) produces a reverse order of s- and p-like valence states. By contrasting the electronic structures of dots as obtained by adirect diagonalization (multiband) pseudopotential approach and by its k.p approximation, we are able to trace the systematic errors of k.p in dots to the k.p errors in the underlying bulk solids. This suggests a 'diagnostic tool' and a strategy for improving the k.p.