Manifestation of hexagonal-like structure in the second-order nonlinear effects in the GaN nanocrystallites

Abstract

Contribution of the hexagonal-like structural components to the photoinduced second harmonic generation (SHG) in GaN large-sized nanocrystallites (with sizes about the 10– 30 nm ) incorporated into the polyvinylalcohol photopolymer matrices is revealed. The SHG measurements were done using pulsed Nd:YAG laser beam ( λ=1.06 μm ; pulse duration τ=15– 50 ps , laser power about 30 MW ) as a fundamental ones and a picosecond nitrogen pulsed laser (P=10 MW; λ=0.377 μm ; pulse time duration τ=10– 25 ps ) as a photoinducing one. We have found that with increasing pumping power density the SHG output signal increases and achieves its maximum value for the power density about 2.6 GW/ cm 2 per pulse. The maximal output photoinduced SHG signal was achieved for parallel directions of the pumping and fundamental beam polarizations. The maximal values of the second-order nonlinear susceptibilities were equal to about 1.09 pm/ V . We have observed an increase of the output SHG below 30 K and for pump-probe delaying time about 18 ps . Substantial contribution to the SHG of wurtzite-like (hexagonal) structural fragments is shown.