S. Yuan et al., MAGNETOREFLECTIVITY OF PB1-XEUXTE EPILAYERS AND PBTE PB1-XEUXTE MULTIPLE-QUANTUM WELLS/, Physical review. B, Condensed matter, 55(7), 1997, pp. 4607-4619
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 magnetoreflectiv
ity in the Faraday configuration (B parallel to[111]) for magnetic fie
lds up to 6 T at 4.2 K. Since the IV-VI lead salt compounds are quite
polar semiconductors, resonant electron-longitudinal-optic- (LO-) phon
on 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 Frohlic
h coupling constants are relevant. However, the CR energies of quasi-t
wo-dimensional (2D) carriers in PbTe wells [n(2D) = (1.5-3) x 10(11) c
m(-2)] of PbTe/Pb1-xEuxTe MQW samples do not exhibit a significant res
onant electron-LO-phonon interaction. This observation is attributed t
o finite-electron concentration effects, in particular, to a partial f
illing of the lowest 2D Landau spin level. The static and dynamic scre
ening of the polar interaction are considered as well, but are ruled o
ut as an explanation for the absence of any remarkable polaron correct
ion 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 s
amples are simulated numerically, using a model for the dielectric res
ponse 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 inc
reasing quantum-well interband energies, a behavior which results from
the strong band nonparabolicity.