MID INFRARED OPTICAL INVESTIGATIONS OF PB1-XEUXSE PARALLEL-TO BAF2 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 absor ption coefficient alpha(omega) and the refractive index n(omega) in th e MIR range for PbSe and Pb1-xEuxSe thin films (x < 5%) deposited by m olecular beam epitaxy (MBE) on (111) BaF2 substrates. X-ray high resol ution diffraction (HRD) measurements gave information on the structura l quality. Transmission experiments have been performed on these sampl es from 800 to 5000 cm(-1) at different temperatures. The treatment of experimental transmission spectra has been done by theoretical calcul ations. The model applying to determine alpha(omega) and n(omega) is b ased on the nonparabolic two-band model (only four fitting parameters) . Using the transfer-matrix method, the best fit to experimental trans mission spectra provides alpha(omega) and n(omega). 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 eps ilon(g) on x and T is established for Pb1-xEuxSe (x < 5%).