Anisotropic Two-Photon Excited Photoluminescence and Optical Constants of InGaN Nanowires

Gallium nitride (GaN) and its derivatives are important materials for optoelectronic and electronic applications, such as light-emitting diodes, solid-state lasers, optical modulators, artificial photosynthesis, etc. Controlled growth and manipulation of these materials at nanoscale dimensions and understanding their linear and nonlinear optical properties lay the foundation for developing next-generation optoelectronic and electronic devices. In this context, herein, we report on the two-photon absorption and anisotropic two-photon excited photoluminescence of InGaN (IGN) nanowires grown by molecular beam epitaxy. The IGN nanowires were imaged using a home-built two-photon photoluminescence microscope with a tunable femtosecond laser to excite over the near-IR range (690-950 nm). In addition, the polarization angle of the excitation electric field was also rotated, and the emitted photoluminescence was analyzed with a polarizer. Results showed polarized photoluminescence with a stronger signal in the direction perpendicular to the IGN nanowires' axis. Also, we observed strong two-photon absorption above the bandgap, with several excitation spectrum peaks near 740, 790, and 870 nm. These peaks showed anisotropic response to the excitation polarization angle, which may be due to the anisotropy of the IGN nanowires' wurtzite phase. The polarized light absorption and emission nature of IGN nanowires, as revealed in this work, may be useful for optimizing materials for future optoelectronic device applications.