Growth and nonlinear characterization of AlN/GaN structures

In this work we present a preliminary study on the influence of the epitaxial growth mode and defect density on second harmonic generation carried out on AlN/GaN structures. The analysed AlN/GaN structures represent the basic unitary cell of a AlN/GaN multilayer structure designed for the enhancement of second harmonic generation. The individual layer thickness is beyond the critical thickness for strain relaxation. The structures were grown on sapphire (Al2O3) substrates using an HT-AlN crystallization layer and morphologically characterized by AFM measurements. Second harmonic generation was observed only in a structure presenting a 3D-like growth mode, obtained for an intermediate value of the V/III ratio and a crystallization layer growth rate of 500 nm h(-1).