Magnetoreflectivity of Pb1-xEuxTe epilayers and PbTe/Pb1-xEuxTe multiple quantum wells

Molecular-beam epitaxy grown n-type Pb1-xEuxTe epilayers (x less than or equal to 0.034) and PbTe/ Pb1-xEuxTe (x less than or equal to 0.039) multiple-quantum-well (MQW) samples were studied by magnetoreflectivity in the Faraday configuration (B parallel to[111]) for magnetic fields up to 6 T at 4.2 K. Since the IV-VI lead salt compounds are quite polar semiconductors, resonant electron-longitudinal-optic- (LO-) phonon coupling (Frohlich coupling) modifies the cyclotron resonance (CR) energies in the Pb1-xEuxTe single epilayers for the three-dimensional (3D) case. Due to the many-valley band structure two different Frohlich coupling constants are relevant. However, the CR energies of quasi-two-dimensional (2D) carriers in PbTe wells [n(2D) = (1.5-3) x 10(11) cm(-2)] of PbTe/Pb1-xEuxTe MQW samples do not exhibit a significant resonant electron-LO-phonon interaction. This observation is attributed to finite-electron concentration effects, in particular, to a partial filling of the lowest 2D Landau spin level. The static and dynamic screening of the polar interaction are considered as well, but are ruled out as an explanation for the absence of any remarkable polaron correction to the CR energies of electrons in the PbTe quantum wells for the range of carrier concentrations investigated. The magnetoreflectivity spectra of Pb1-xEuxTe single layers and PbTe/Pb1-xEuxTe quantum well samples are simulated numerically, using a model for the dielectric response of IV-VI compounds in a magnetic field, which also includes the electron-LO-phonon interaction. The transverse and longitudinal masses, and thus also the interband momentum matrix elements are determined for Pb1-xEuxTe as a function of the composition up to x < 0.034. It is found that the transverse mass increases with Eu content, whereas the longitudinal one nearly stays constant. The 2D CR masses of electrons in the PbTe wells increase with decreasing well width, i.e., with increasing quantum-well interband energies, a behavior which results from the strong band nonparabolicity.