Piezoelectric polaron and polaron pinning inn−CdS

Abstract

The cyclotron resonance of the piezoelectric polaron in $n\ensuremath{-}\mathrm{C}\mathrm{d}\mathrm{S}$ has been investigated using far-infrared spectroscopy at magnetic fields to 90 kOe. Both lamellar grating and Michelson Fourier-transform spectrometers were used with a 0.3-K Ge bolometer to study the photon energy region from 10 to 60 ${\mathrm{cm}}^{\ensuremath{-}1}$. The theory of Miyake predicts that the frequency of the polaron's cyclotron resonance is shifted from the bare band electron resonance frequency according to the expression $\frac{\ensuremath{\Delta}{\ensuremath{\omega}}_{c}^{p}}{{\ensuremath{\Omega}}_{c}} \ensuremath{\propto} {H}^{\ensuremath{-}1}{T}^{\frac{2}{3}}$. The magnetic field dependence of the present cyclotron resonance confirms this expression; the cyclotron mass is decreased by piezoelectric polaron effects. The bare band mass in $n\ensuremath{-}\mathrm{C}\mathrm{d}\mathrm{S}$ has also been determined by taking into account the Fr\ohlich polaron interaction in addition to the piezoelectric polaron effects. For $H$ parallel to the $c$ axis this cyclotron mass is $(0.155\ifmmode\pm\else\textpm\fi{}0.005)m$. Finally, the polaron pinning due to the 43-${\mathrm{cm}}^{\ensuremath{-}1}$ optically inactive phonon has been observed.