Electronic and Optical Properties of Group-III-Nitride Semiconductor Quantum Dots

Embedded semiconductor quantum dots (QDs) based on group-III-nitrides exist in the zincblende or the wurtzite structure. To model the electronic structure of these nanostructures, we start from a tight-binding (TB) model for the bulk system. Two different approaches are used, namely the "empirical tight-binding model" (ETBM) and the "effective bond-orbital model" (EBOM). Whereas the ETBM starts from an atomic basis, effective orbitals on the Bravais lattice sites are used as the TB-basis of the EBOM. The TB-parameters are determined so that the essential properties of the bulk band structure are reproduced. These TB-models can be applied to calculate the electronic states of QDs by using the respective TB-parameters for the QD and barrier sites. Results for the discrete QD-spectra and for the one-particle states (and their symmetry properties) obtained within ETBM and EBOM are presented and compared, showing essentially good agreement between the two methods for a truncated pyramidal GaN/AlN QD. A many-body model Hamiltonian with a coupling to an optical field is constructed, which allows for a calculation of the optical spectra of the QD. As an example, we discuss the excitonic absorption spectrum of a lens-shaped wurtzite InN/GaN QD.