C, Si, Ge AND Sn SURFACE DOPING OF WURTZITE AlN NANOCRYSTALS: Ab INITIO STUDY USING WURTZOIDS STRUCTURES

Wurtzite nanostructures have been recently described using molecular building blocks called wurtzoids. These wurtzoids are utilized in the present work to describe aluminum mononitride (AlN) nanostructures including its surface doping with group IV elements i.e. C Si, Ge and Sn. Calculations are performed for bare, and hydrogen surface passivated wurtzoids. Results show that hydrogen-passivated (HP) AlN-wurtzoids have energy gaps that are very near to the experimental bulk AlN. Longitudinal optical (LO) vibrational frequencies are also very near to bulk experimental value with blue and red frequency shifting for bare, and hydrogen surface passivated wurtzoids. Doped AlN-wurtzoid2c with group IV elements show a reduction of the energy gap. The gap generally decreases as the atomic number of the dopant increases. The electronic and vibrational properties can be interpreted using the charge transfer between atoms. Minimum atomic charge transfer is for carbon atom doping that leads to a maximum reduction of the energy gap of bare and entirely hydrogen surface passivated wurtzoids. The doped carbon atom charge transfer also induces the highest increase in LO vibrational mode.