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

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linear and nonlinear properties in this thesis assume that GaN is isotropic. The justification
of this assumption follows. All samples investigated in this work are grown
with the c axis, or the extraordinary axis, normal to the surface. The extraordinary
index is related to the ordinary index by ne - no ~ 0.02 [58]. Assuming the incident
wave is polarized in the plane containing the extraordinary a.xis, the index of
refraction for light propagating with an angle () to the in the extraordinary axis is
[60]
(-lA-l )
In all of our linear and nonlinear experiments, the angle of between the incident
beam and the surface normal is less than 75° . The light transmitted into the Ga~
sample refracts such that the angle between extraordinary axis and the direction of
propagation is reduced to less than 24° . Using equation (4.44), we estimated that
our optical experiments always probe an effective index of refraction that is within
0.15% of the ordinary index. This correction alters the phase of light traversing a
GaN film by at most 2° .
c"sing the transmission measurement, we also determined the absorption constant
for GaN in the vicinity of the band gap (",3.4 eV). Absorption can be included
in the matrix-transmission theory by multiplying the transmission coefficient, T. in
equation (4.6) bye-ad. The coefficient Q
is related to the imaginary part of the index
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