Optical constants of InN thin films on (111) GaAs grown by reactive magnetron sputtering

Abstract

The optical constants of InN thin films on (111) GaAs substrates grown by rf reactive magnetron sputtering under different growth conditions have been investigated both theoretically and experimentally in the range from the free-carrier absorption region to the above band gap region (0.2–3.0 eV). A model of dielectric function for InN is developed, which includes four different mechanisms corresponding to interband transition contribution, excitonic contribution, free-carrier contribution, and background dielectric contribution. The contribution of free-carrier absorption to dielectric function has been introduced for the study of optical constants in InN thin films. By employing the model, we obtain the refractive index, extinction coefficient, and absorption coefficient as a function of photon energy, as well as the free-carrier concentration. The refractive index (n) and the extinction coefficient (k) of InN thin films near the band gap are found to be almost independent of the growth conditions. In contrast, in the free-carrier absorption region, the values of n and k are strongly related to the free-carrier concentration for different samples. The relationship between the free-carrier concentration and the film quality has also been studied.