ISSN 1063-7834, Physics of the Solid State, 2011, Vol. 53, No. 4, pp. 810–814. © Pleiades Publishing, Ltd., 2011. Original Russian Text © E.S. Zhukova, N.P. Aksenov, B.P. Gorshunov, Yu.G. Selivanov, I.I. Zasavitskii, D. Wu, M. Dressel, 2011, published in Fizika Tverdogo Tela, 2011, Vol. 53, No. 4, pp. 755–759. 810 1. INTRODUCTION The properties exhibited by europium chalco- genides EuX (X = O, S, Se, Te), which form a separate class of magnetic semiconductors, are adequately described in the literature [1–3]. Currently, they become of interest again in connection with the use of solid solutions on their base for the design of semicon- ductor heterostructures with effective electron and optical confinement [4–6] and the fabrication of highly reflecting Bragg mirrors [7] in mid-infrared (IR) spectral region. Such mirrors have been used to develop both IR lasers with vertical emission output (VCSEL, vertical cavity surface emitting laser) [7] and highly selective IR detectors (RCED, resonant cavity enhanced detector) [8]. Data on the optical properties of the Pb 1– x Eu x Te solid solutions are very scarce. First measurements of photoluminescence of the Pb 1– x Eu x Te solid solution [4] showed that band gap E g of the compound abruptly and nonlinearly increases as the Eu content increases. Dispersion of the absorption and refraction index in Pb 1  x Eu x Te (0 < x < 0.05) at energies above and below E g (E g /hc ~ 1000–5000 cm –1 , c is the velocity of light, and h is the Plank constant) and at low temperatures (5–300 K) was studied in [9]. Using the technique of inclined incidence when measuring the transmission spectra, Aigle et al. [10] concluded that the Pb 1  x Eu x Te solid solution manifests a dual-mode behavior with a local mode of Eu in PbTe at 127 cm –1 . They also determined energies of optical phonons in EuTe at 5 K. In order to obtain a detailed information about interactions of Eu ions located in the crystal matrix of the IV–VI semiconductor, further optical measure- ments in the mid-IR and far-IR spectral regions should be performed. We originally measured the transmission spectra of epitaxial layers of the Pb 1  x Eu x Te solid solution grown on the BaF 2 and Si substrates in a wide frequency range at temperatures from room temperature to liquid-helium temperature. 2. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUE Single-crystal Pb 1– x Eu x Te (0 ≤ x ≤ 0.37) layers were grown by molecular beam epitaxy [11] on cleaved insulating BaF 2 substrates. Selection of these sub- strates is caused by the fact that BaF 2 and lead– europium chalcogenides have close linear thermal expansion coefficients, which allows us to repeatedly cool samples to low temperatures. However, BaF 2 is characterized by strong phonon and impurity absorp- tion in a range of 100–600 cm –1 , which makes the measurements of transmittance of the layers in this spectral range impossible. Therefore, for the composi- tion with x = 0.07, we grew layers on a high-resistivity (ρ ~ 50 kΩ cm) Si(111) substrate with CaF 2 /BaF 2 buffer layers 1 according to technology described in 1 Silicon substrates with CaF 2 /BaF 2 buffer layers were fabricated at the Institute of Electronic Engineering and Industrial Tech- nologies, Academy of Sciences of Moldova. OPTICAL PROPERTIES Transmission Spectra of Epitaxial Layers of Pb 1– x Eu x Te (0 ≤ x ≤ 0.37) Solid Solutions in the Frequency Range 7–4000 cm –1 E. S. Zhukova a, *, N. P. Aksenov a , B. P. Gorshunov a , Yu. G. Selivanov b , I. I. Zasavitskii b , D. Wu c , and M. Dressel c a Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 117942 Russia * e-mail: zhukovaelenka@gmail.com b Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia c Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, Stuttgart, D-70550 Germany Received July 15, 2010; in final form, September 30, 2010 Abstract—The spectra of epitaxial Pb 1– x Eu x Te (0 ≤ x ≤ 0.37) solid solution layers grown on BaF 2 and Si sub- strates have been investigated over a wide frequency range 7–4000 cm –1 at temperatures of 5–300 K. Apart from the phonon and impurity absorption lines, the absorption in a local mode in PbEuTe layers of substrates and buffer layers has been observed in the frequency range 110–114 cm –1 . As the temperature decreases from 300 to 5 K, the transverse phonon mode softens from 33.0 to 19.5 cm –1 . DOI: 10.1134/S1063783411040342