Comparison of optical properties between Wurtzite and zinc-blende Ga0.75Al0.25N

In order to compare optical properties of Wurtzite and zinc-blende Ga0.75Al0.25N and lay a foundation for preparation of Ga0.75Al0.25N photocathodes, absorption coefficient, complex refractive index, dielectric function, reflectivity and loss function of Ga0.75Al0.25N in two forms are calculated using first principle based on density functional theory. Results show that zinc-blende Ga0.75Al0.25N owns smaller band gap than Wurtzite Ga0.75Al0.25N, and its conduction band is more broad. The optical properties differences of two structures mainly occur at the range of 8.6–26.0 eV. The peaks of imaginary dielectric function and absorption curves are at higher energy point for zinc-blende Ga0.75Al0.25N. The highest absorption of Wurtzite Ga0.75Al0.25N is 351386.171/cm at 11.05 eV, which is smaller than zinc-blende of 437809.895/cm at 13.84 eV. The average reflectivity of Wurtzite Ga0.75Al0.25N is lower than that of zinc-blende Ga0.75Al0.25N. The results are conductive for designing component structures of Ga0.75Al0.25N photocathodes.