William Angerer - Department of Physics and Astronomy - University ...

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5.3 Defects in GaN
Recently, intense experimental and theoretical effort has been applied to understand
the nature of defect states in GaN. The goals of this effort include the identification
of the prevalent defect species, determination of the growth conditions that lead to
defects, and elimination of defect states to optimize GaN electro-optic performance
characteristics. Defect states adversely affect the electrical characteristics of semiconductors
by trapping carriers. This trapping degrades the mobility of the conducting
material. Defect states also offer both radiative and nonradiative electron-hole recombination
routes that compete with the preferred radiation channel, i.e. the defect
states degrade the preferred luminescent properties of the material. We briefly review
some of the experimental and theoretical work on this subject for two reasons. First,
defect states are present in GaN regardless of growth technique or doping. Second,
our study was motivated in part to elucidate the role of defect states on the nonlinear
optical properties of GaN.
Perhaps the most commonly postulated defect state in GaN is the nitrogen vacancy,
Vv [53, 76, 84, 85, 86].
The ubiquitous high n-type conductivity of Ga~
suggests that the conduction electrons are due to a native defect, as opposed to a
contaminant which has lower concentrations than the conduction electrons. Using ab
initio molecular dynamics calculations, Boguslawski and coworkers identified \iN and
the gallium interstitial, I(Ga), as defect states most likely to be responsible for the
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