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Mid Infrared Optical Investigations of Pb 1 ÿ xEuxSe k BaF 2 Thin Films Grown by MBE

IV±VI semiconductor compounds are interesting in the mid-infrared (MIR) range for optoelectronic applications because these compounds have a narrow direct bandgap in this frequency range. Our study presents the determination of the optical constants dispersion which are the absorption coefficient a(w) and the refractive index n(w) in the MIR range for PbSe and Pb1± xEuxSe thin films (x < 5%) deposited by molecular beam epitaxy (MBE) on (111) BaF2 substrates. X-ray high resolution diffraction (HRD) measurements gave information on the structural quality. Transmission experiments have been performed on these samples from 800 to 5000 cm 1 at different temperatures. The treatment of experimental transmission spectra has been done by theoretical calculations. The model applying to determine a(w) and n(w) is based on the nonparabolic two-band model (only four fitting parameters). Using the transfer-matrix method, the best fit to experimental transmission spectra provides a(w) and n(w). The results are in agreement with those already published on PbSe materials and are new for Pb1± xEuxSe epilayers. Moreover, the dependence of the band gap eg on x and T is established for Pb1± xEuxSe (x < 5%).