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The electronic states of a singly ionized on-axis double-donor complex (D2+) confined in two identical vertically coupled, axially symmetrical quantum dots in a threading magnetic field are calculated. The solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are shown for bonding and antibonding lowest-lying artificial molecule states corresponding to different quantum dot morphologies, dimensions, separation between them, thicknesses of the wetting layers, and magnetic field strength.

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Ab-initio density functional theory calculations are carried out to investigate the role of zirconium (Zr) impurity atoms during AlN(0001) surface growth. Adsorption and diffusion of Zr atoms on AlN(0001)-2 Â 2 surface is examined and it is shown that Zr atoms preferentially adsorb at the T4 sites at low and high coverage (from 1/4 up to 1 monolayer). We found that the Zr adatom diffusion energy barrier between the T4 and H3 sites is around $0.4 eV, which is an indication of a significant Zr adatom diffusion on this surface. In addition, calculating the relative surface energy of several configurations and various Zr concentrations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Zr and Al chemical potentials. Based on these results, we find that incorporation of Zr adatoms in the Al-substitutional site is energetically more favorable compared with the adsorption on the top layers. This effect leads to the formation of a nonreactive interfacial ZrN(111) layer on the AlN(0001) surface, which can offer a good interfacial combination between AlN substrate and other metal contacts, i.e. zirconium.

We consider a model of hydrogen-like artificial molecule formed by two vertically coupled quantum dots in the shape of axially symmetrical thin layers with on-axis single donor impurity in each of them and with the magnetic field directed along the symmetry axis. We present numerical results for energies of some low-lying levels as functions of the magnetic field applied along the symmetry axis for different quantum dot heights, radii, and separations between them. The evolution of the Aharonov-Bohm oscillations of the energy levels with the increase of the separation between dots is analyzed.