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

142
Fig. 6.2 displays the azimuthal dependence of SHG for GaN in the p-in/p-out
and s-in/p-out polarizations at an angle of incidence of 15°. The p-in/p-out and s­
in/p-out polarized SHG data exhibit a one-fold symmetric modulation. These data
are inconsistent with misaligned polarizers, which would result in non-zero isotropic
signals for both polarizations. On the other hand, a simple sample miscut model was
applied successfully to interpret the data. A miscut between the normal to the surface
and the z-a.xis of the crystal results in a precession of the z-a.xis about the surface
normal during the azimuthal scan. This precession induces an azimuthally dependent
coupling of the fundamental fields to generate the anisotropic second-harmonic signal.
Assuming the angle between the surface normal and the z-a.xis of the crystal is o.
X~~k,lab is related to x~2J~ystal by equation (6.1) but with equation (6.2) replaced by
cos 1> sin 0 coso 0 -sino
Rmiscut = - sin ¢> cos 0 0 0 1 (6.3)
0 0 1 sin 0 0 cosa
2\iote, equation (6.3) assumes the [0001] a.xis is miscut in the xz plane. Since the
x- and y-a.xes of GaN are equivalent, this assumption simply produces a phase shift
between the experimental and calculated data. Table 6.2 displays the calculated azimuthal
dependence of SHG from GaN [0001] with a small miscut angle, o. Note that
higher order terms in the miscut, i.e. terms with miscut dependences of sin 2 0
and
sin 3 o, are not displayed. The best fits to the p-in/p-out and s-in/p-out data yield a
sample miscut angle, 0, of 0.80° ± 0.05°. The data were fitted with a function that
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.