Nonlinear optical response of GaN layers on sapphire: The impact of fundamental beam interference

GaN layers grown by metalorganic chemical-vapor deposition were characteriz ed by optical second- and third-harmonic generation techniques. The angular dependence of the second-harmonic intensity in transmission showed a c-tex tured growth of the GaN layers on the sapphire substrates. The measured rat ios d(33)/d(15) and d(33)/d(31) are equal to -2.02 and -2.03, respectively, which is indicative of a wurzite structure of the GaN layers. The measured d(33) is 33 times that of the d(11) of quartz. Fine oscillations were obse rved in the measured second- and third-harmonic angular dependencies that a re explained by taking into account the interference of the fundamental bea m in the GaN/sapphire structure. (C) 2000 American Institute of Physics. [S 0003-6951(00)03907-3].