Microwave magnetoplasma study of lattice and electronic properties of PbTe

The $q=0\mathrm{}$ transverse-optic-phonon frequency ${\omega }_{\mathrm{TO}}$ has been determined in PbTe from microwave magnetoplasma experiments at frequencies near 70, 138, and 335 GHz, over the temperature range $4.2\le T\lesssim 80$ K. Both $n$-type and $p$-type bulk samples and $p$-type epitaxial thin films on Ba${\mathrm{F}}_2$ substrates were studied. At the lowest temperatures, ${\omega }_{\mathrm{TO}}$ is almost temperature independent and has the value 12.3 ± 1.0 ${\mathrm{cm}}^{-1\mathrm{}}$. This implies, via the Lyddane-Sachs-Teller relation, a static lattice dielectric constant ${\epsilon }_s\cong 3000$, depending on the value assumed for the high-frequency dielectric constant ${\epsilon }_{\infty }$. At temperatures above 30 K, ${\omega }_{\mathrm{TO}}$ shows a temperature dependence which is consistent with Curie-law behavior of the static lattice dielectric constant, ${\epsilon }_s\propto {(T-T_C)}^{-1\mathrm{}}$. Curie temperatures near both - 150 and - 80 K were found, but the favored experimental value is $T_C=-151\mathrm{}\pm 7$ K. Several band-edge electronic parameters were also determined: transverse-conduction-band-edge effective mass, $\frac{m_{1c}}{m_0}=0.0164\mathrm{}\pm 0.001$; transverse-valence-band-edge effective mass, $\frac{m_{1v}}{m_0}=0.021\mathrm{}\pm 0.001$: valence-band-edge mass anisotropy ratio, $K_{0v}=13.4\mathrm{}\pm 2.0$. The critical importance of sample preparation and characterization procedures is discussed, together with possible reasons for the discrepancies among previously reported values of ${\epsilon }_s$, which scatter over two orders of magnitude.