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

Appendix E
Effect of Sapphire Miscut on Nonlinear Optical Measurements
In section 6.2 we stated that rotational symmetry measurements of GaN in the s-out
polarization are not useful as probes of thin film symmetry. Difficulty in extracting
GaN symmetry data from this measurement stems from the birefringence of the
sapphire substrate. In this appendix we discuss the effect of the miscut sapphire
substrate on the nonlinear optical symmetry measurements of GaN.
Sapphire is a negative unia.xial crystal. For samples in which the extraordinary
axis is miscut slightly from the normal to the sample, rotation of the sample about its
normal causes the precession of the extraordinary axis. This results in transmission
of p-polarized light, which depends on the rotation angle of the crystal.
vVe can model this effect as follows. vVe define three coordinate systems: the
coordinate system of the polarizer, the coordinate system in which the laser beam
is incident on the GaN /sapphire sample, and the coordinate system of the sample.
These will be denoted by superscripts as p (polarizer), I (lab), and c (crystal), respec-
222
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.