Dielectric function and critical points of AlP determined by spectroscopic ellipsometry

•We report the dielectric function ε of AlP from 0.74 to 6.54 eV.•The critical points (CPs) in the E2 spectral range are important for band-structure analysis.•We extract ε of AlP, using the multilayer parametric model.•The CP energies are obtained from numerically calculated second-energy-derivatives.•We identify these CPs from the linear augmented Slater-type orbital method.

We report the room-temperature dielectric function ε of AlP from 0.74 to 6.54 eV obtained by in situ spectroscopic ellipsometry. Measurements were done on a 1.2 μm thick film grown on (0 0 1) GaAs by molecular beam epitaxy, with ε extracted using a multilayer parametric model. Critical point energies of features in the ε spectra were obtained from numerically calculated second-energy-derivatives, and their Brillouin-zone origins identified by band-structure calculations done using the linear augmented Slater-type orbital method.