Nonlinear optical characterization of GaN layers grown by MOCVD on sapphire

Optical second and third harmonic generation measurements were carried out on GaN layers grown by metalorganic chemical vapor deposition (MOCVD) on sa pphire substrates. The measured d(33) is 33 times the d(11) of quartz. The angular dependence of second-harmonic intensity as well as the measured rat ios d(33)/d(15) = -2.02 and d(33)/d(31) = -2.03 confirm the wurzite structu re of the studied GaN layers with the optical c-axis oriented perpendicular to the sample surface. Fine oscillations were observed in the measured sec ond and third harmonic angular dependencies. A simple model based on the in terference of the fundamental beam in the sample was used to explain these oscillations.