Optical anisotropy of strongly photonic porous gallium phosphide

Porous gallium phosphide layers displaying a remarkably a strong in-plane anisotropy in the visible and infrared ranges have been fabricated using a (110)-oriented single-crystal substrate. Methods of ellipsometry and Fourier-transform infrared spectroscopy are employed to measure the dispersion of refractive-index anisotropy in these Gap layers. Dispersion of the refractive index in these samples is shown to be normal, with its magnitude reaching 0.1 for 633-nm radiation. Anisotropic porous GaP samples studied in this work simultaneously exhibit unique photonic properties, induced by a strongly scattering network of pores, and display features of an optically negative uniaxial crystal with an optical axis oriented along the [110] direction.