Influence of electron scattering on phonon–plasmon coupled modes dispersion and free-electron absorption in n-doped GaN semiconductors at mid-IR wavelengths



The model to calculate the free-carrier absorption coefficient for polar III–V semiconductors with strong LO phonon–plasmon interaction was generalized by taking into account free-carrier scattering by defects The following main mechanisms assisting in the photon absorption process, where taken into account: thermal phonon-like branch and plasmon-like branch scattering, impurity scattering, and acoustic phonon scattering. To calculate the contributions of phonon–plasmon coupled modes into the absorption coefficient, the integral dispersion equation for coupled mode frequencies was obtained taking into account free electron scattering by imperfections (mainly by charged impurities in highly doped semiconductors); the dispersion relation of phonon–plasmon coupled modes were calculated versus electron concentration. Computations are performed for α-GaN and GaN doped semiconductors at different mid-IR wavelengths and electron concentrations. For all considered cases, the relative difference between the Drude model calculation results based on static and dynamic damping factors is typically smaller than (25–35)%.