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Wurtzite AlN(0001) Surface Oxidation: Hints from Ab Initio Calculations
journal contribution
posted on 2018-08-20, 00:00 authored by Zhi Fang, Enhui Wang, Yafeng Chen, Xinmei Hou, Kuo-Chih Chou, Weiyou Yang, Junhong Chen, Minghui ShangWith
superior electrical and thermal properties, aluminum nitride
(AlN) exhibits wide application. However, AlN is rather oxygen-sensitive
and tends to be oxidized at high temperature. The surface oxidation
of AlN remains a major challenge, while the underlying physics of
AlN surface oxidation is still elusive. Here, First-principles calculations
were performed to study wurtzite AlN(0001) surface oxidation process.
The adsorption energy of oxygen was calculated to be site-dependent
on the surface with varying O coverage. Calculation indicates that
oxygen atoms are preferentially adsorbed at the hollow site (H3) of
the AlN(0001) surface regardless of the O coverage. N2 is
determined as the dominant gas product. The procedure of N3– removal and the formation of N vacancies (VN) take place
step by step. VN plays an accelerating role in the oxidation
of AlN, and O2– prefers to occupy the site of VN via consuming the Al p lone-pair electrons and passivating
the dangling bond states of Al. An O–Al–O layer is formed
when the first Al–N bilayer is fully oxidized, which could
be regarded as a precursor of γ-Al2O3.
On the basis of our atomic-level simulation, a possible phase transformation
mechanism from γ-Al2O3 to α-Al2O3 was further proposed.