Magnetophonon and Shubnikov-de Haas oscillations inn-type PbTe epitaxial films

We have observed Shubnikov-de Haas (SdH) and magnetophonon (MP) oscillations in the magnetoresistance of single crystal, vapor-phase, epitaxial films of $n-\mathrm{PbTe}$ on Ba${\mathrm{F}}_2$ substrates. For a film with $n=6\mathrm{}\times {10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$, the SdH oscillations show that all electrons are in a single valley at 4.2 K. This result is a consequence of a thermally induced shear strain which pulls the valleys toward the bismuth structure. Both the cyclotron mass and cross-section anisotropy of the corresponding ellipsoid were obtained. Several series of MP oscillations were detected. Use of the measured cyclotron masses allows each series to be identified with intravalley scattering by long-wavelength LO phonons with energies of about 14 meV.