Defects in hexagonal-AlN sheets by first-principles calculations
Tóm tắt
Theoretical calculations focused on the stability of an infinite hexagonal AlN (h-AlN)
sheet and its structural and electronic properties were carried out within the framework
of DFT at the GGA-PBE level of theory. For the simulations, an h-AlN sheet model system
consisting in 96 atoms per super-cell has been adopted. For h-AlN, we predict an Al-N bond
length of 1.82 Å and an indirect gap of 2.81 eV as well as a cohesive energy which is by
6% lower than that of the bulk (wurtzite) AlN which can be seen as a qualitative
indication for synthesizability of individual h-AlN sheets. Besides the study of a perfect
h-AlN sheet, also the most typical defects, namely, vacancies, anti-site defects and
impurities were also explored. The formation energies for these defects were calculated
together with the total density of states and the corresponding projected states were also
evaluated. The charge density in the region of the defects was also addressed.
Energetically, the anti-site defects are the most costly, while the impurity defects are
the most favorable, especially so for the defects arising from Si impurities. Defects such
as nitrogen vacancies and Si impurities lead to a breaking of the planar shape of the
h-AlN sheet and in some cases to the formation of new bonds. The defects significantly
change the band structure in the vicinity of the Fermi level in comparison to the band
structure of the perfect h-AlN which can be used for deliberately tailoring the electronic
properties of individual h-AlN sheets.
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