Optical characterization of p-doped InP epitaxial layers in mid and far infrared region*

The optical properties of p-doped Indium Phosphide (InP) epitaxial thin films with 1, 3, and 24 $\times $ 10$^{18}$ cm$^{-3}$ carrier concentrations were investigated by infrared reflection, transmission, and absorption measurements in 5 - 40 $\mu $m wavelength range. The absorption spectra were modeled by complex dielectric function using the classical Lorentz--Drude model. The phonon absorption in InP was modeled using eight Lorentzian oscillators. This method gives a straightforward approach for modeling the experimental absorption spectra when compared to the two-phonon absorption spectroscopy technique. The calculated spectra are in a good agreement with experimental spectra. The effects of doping on fitting parameters are also investigated.