We have investigated the atomic structure, the electronic
structure,
and the formation energies of all native point defects in GaN, in their
various charge states. The figure above displays the electronic defect
wave function for some of the defects.
Our main conclusions are:
-
Self-interstitials and antisites have very large formation energies,
and
are hence unlikely to occur.
-
Gallium vacancies may form a source of compensation in n-type
material,
and nitrogen vacancies may compensate p-type material.
-
Nitrogen vacancies act as donors, but have a very high formation energy
in n-type material. We therefore think it is unlikely that the
commonly
observed n-type conductivity of as-grown GaN can be attributed
to
nitrogen vacancies. This conductivity is due to unintentional
incorporation
of donor-type impurities such as silicon or oxygen.
-
The nitrogen vacancy can assume two charge states (+ and 3+); the
asssociated
metastability is the likely explanation for the observed persistent
photoconductivity
in p-type GaN.
-
Gallium vacancies are the likely source of the commonly observed
"yellow
luminescence".
For more information:
"Atomic geometry and electronic structure of native defects in GaN", J.
Neugebauer and C. G. Van de Walle, Phys. Rev. B 50, 8067 (1994)
(RC).
"Native defects and impurities in cubic and wurtzite GaN", J.
Neugebauer
and C. G. Van de Walle, in Diamond, SiC and Nitride Wide Bandgap
Semiconductors,
edited by C. H. Carter Jr., G. Gildenblat, S. Nakamura, and R. J.
Nemanich,
Materials Research Society Symposia Proceedings, Vol. 339 (Materials
Research
Society, Pittsburgh, Pennsylvania), p. 687.
"Gallium vacancies and the yellow luminescence in GaN", J. Neugebauer
and
Chris G. Van de Walle, Appl. Phys. Lett. 69, 503 (1996).
"Native defects, impurities, and doping in GaN and related compounds:
general
remarks"; "Native point defects in GaN and related compounds"; "Yellow
luminescence in GaN"; C. G. Van de Walle et al. in Properties,
Processing and Applications of Gallium Nitride and Related
Semiconductors,
edited by J. Edgar, S. Strite, I. Akasaki, H. Amano, and C. Wetzel,
EMIS
Datareview Series No. 23 (INSPEC, IEE, 1999), pp. 275-280; 281-283;
313-316.
“First-principles calculations for defects and impurities:
Applications to III-nitrides” (Applied Physics Review), Chris G. Van de
Walle and J. Neugebauer, J. Appl. Phys. 95, 3851 (2004).
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