Internal fields in InN/GaN quantum dots: Geometry dependence and competing effects on the electronic structure

Self-assembled InN quantum dots grown on lattice-mismatched GaN substrates are subject to internal structural and electrostatic fields originating mainly from: (1) the fundamental crystal atomicity and the interface discontinuity between two dissimilar materials, (2) atomistic strain, (3) piezoelectricity, and (4) spontaneous polarization (pyroelectricity). In this paper, using the multimillion-atom NEMO 3-D simulator, we study the origin and effects of these four competing internal fields on the electronic structure of self-assembled InN/GaN quantum dots having three different geometries, namely, box, dome, and pyramid. It is shown that internal electrostatic fields in InN/GaN quantum dots are long-ranged (demanding simulations using millions of atoms) and lead to a global shift in the one-particle energy states, significant modifications in the valence bandstructure (pronounced carrier localization), anisotropy and twofold degeneracy in the conduction band P level, formation of mixed excited bound states, and polarized optical transitions near the Brillouin zone center.