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

80
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GaN
A12a3
index fluid
glass slide
Figure 4.2: Schematic of the GaN sample with index matching fluid and glass slab.
This experimental setup suppressed reflected light from the back sapphire surface.
The reflection data from the GaN/sapphire/index fluid/glass slab matched the
calculated reflection from a GaN film on a semi-infinite slab of sapphire more closely
than theoretically predicted. vVe define the average normalized error introduced by
the glass substrate as
(j= ( 4.2)
where I;apphire represents the theoretically predicted reflection coefficient at an angle
of incidence of i degrees from a GaN film on a sapphire semi-infinite substrate. Iflass
represents the refiection from GaN grown on sapphire followed by a semi-infinite glass
slab. N is the total number of points at which (j was evaluated, i.e. .V = 15. \Ve
calculated (j = .094 but measured (j = .016. Possible explanations for this discrepancy
include a nonuniform thickness of the sapphire substrate and the finite divergence of
the ReNe beam. Both of these effects damp the oscillations from the interference of
the light multiply reflected from the GaN film and the sapphire substrate.
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