GaN film optical nonlinearity: wavelength dependent refractive index for All-Optical switching application

Abstract

Gallium Nitride (GaN) is fast becoming a potential replacement for silicon in complex electronic and photonics circuitries and systems. At higher optical intensity, optical effects such as non-linear effects would become non-trivial. To this end, we investigated nonlinear optical properties of metal–organic chemical vapor deposited GaN. Specifically, continuous-wave laser Z-scan techniques were employed to obtain nonlinear refractive index, n2, of a 1-µm thin layer on a c-plane sapphire substrate. FESEM, PL, XRD and EDS analysis confirmed the good quality growth of GaN thin film. We detected a reversal of polarity of the n2 value at 637 nm and 405 nm of CW laser excitation and femtosecond laser pulse at 808 nm. This is substantiated by theoretical calculation of GaN’s n2 showing sign switchover at wavelength shorter than 420 nm. This presents a new all-optical switching scheme based on the switchover of wavelength dependent n2. These findings point to opportunities for GaN-based integrated photonics for nonlinear and quantum photonics applications.