Electronic and optical properties of PbTe/${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Eu}}_{\mathit{x}}$Te multiple-quantum-well structures

The frequency dependence of the absorption constant α(ω) and the enhancement of the refractive index n(ω) in the region of interband transitions between confined quasi-two-dimensional states of the valence and conduction bands of PbTe/${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$Te multiple-quantum-well (MQW) structures is studied experimentally as well as theoretically. Transmission, reflectivity, and photoconductivity spectra of several MQW’s with PbTe well widths from 62 to 118 Å and ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$Te barrier widths from 486 to 621 Å (x≊3%) are compared with calculated spectra. The experimental data are compared to calculations of the transmission and reflectivity of the multilayer structures based on frequency-dependent dielectric functions ε(ω) of the buffer and MQW layers. For the buffer layer experimentally determined values for ε(ω) are used, whereas for the MQW system the sum of a background dielectric function and an additional term, which takes into account the electronic contribution due to interband transitions between electric subbands in the valence band (VB) and conduction band (CB), are used.