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

•Good quality GaN film fabricated by MOCVD is confirmed via FESEM, EDS, AFM, XRD, UV–Vis and PL analysis.•Z-scan reveals the nonlinear absorption and nonlinear refraction properties of GaN thin film via 440 nm, 637 nm and 808 nm laser.•We detected a reversal of polarity of the nonlinear refractive index, n2 at 637 nm and 405 nm of CW laser excitation and femtosecond laser pulse at 808 nm.•Novel all-optical dual beam switching scheme based on n2 sign switchover of GaN is proposed.