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

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high intrinsic electron concentrations in GaN. However, other researchers ~eugebauer
and Van de vValle do not believe this mechanism for the n conductivity, i.e. V,y [87].
They instead suggest that the dominant defect in n-type GaN is VCa and in p-type
GaN is \IN,
Table 5.3 summarizes some of the experimental work in this field 2 . ~o consensus
as to the nature of defects states in GaN has been reached. and this area remains a
rich field for research.
5.4 Application of Group Theory to Optical Process
In this section. we analyze the relationship between the nonlinear optical properties of
Ga~ and its band structure. This analysis is formulated in terms of group theory and
selection rules. This section assumes the reader has some familiarity with abstract
group theory. specifically character tables, irreducible representations, and group multiplication
tables. The reader is referred to [36, 91, 92] for excellent discussions of
abstract group theory and its application to solid state systems.
The general question we want to answer is: given the band structure of Ga~.
how can we determine which bands contribute to the nonlinear optical spectrum.
The quantum mechanical expression for the second-order nonlinear susceptibility.
21n Table 5.3 "?" refers to an unidentified defect, cb refers to the conduction band level. and \·b
refers to the valence band level.
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