POLARON CYCLOTRON-RESONANCE AND IMPURITY EFFECTS IN II-VI SEMICONDUCTORS AT ULTRA-HIGH MAGNETIC-FIELDS UP TO 210-T

We have observed cyclotron resonance and impurity cyclotron resonance in II-VI semiconductors, n-type CdS, n-type ZnSe and n-type ZnS over a wide far-infrared wavelength range between 9.25 mum and 119 mum under pulsed high magnetic fields up to 210 T. Since the electron-phonon interaction is significantly large in these materials, a very large resonant polaron effect was observed near the longitudinal-optical (LO) phonon energy. The experimental results of cyclotron resonance were found to be in good agreement with a theoretical calculation in n-type ZnSe and CdS. Moreover, in n-type CdS, many unidentified absorption peaks were observed at low temperature. In n-type ZnS, we present the first observation of cyclotron resonance.