FIR-magnetospectroscopy on HgSe:Fe quantum dots

We report on FIR-magnetospectroscopy on HgSe:Fe quantum dots in DC-magnetic fields up to plusmn12 T at He-temperatures. The epitaxially grown samples, which were already characterized by megagauss magnetospectroscopy in the near infrared, were investigated using an Abmm-vector analyzer in connection with a superconducting solenoid. Both, cavity detuning experiments as well as direct transmission in Faraday configuration for unpolarized and linearly polarized radiation were performed for monochromatic radiation in the frequency range between 35 GHz and 300 GHz. The temperature was varied between 2 K and 190 K. The observed magnetic field dependent structure meets the expectation of the broad Drude- type cyclotron resonance for low mobility at small resonance field in agreement with the previous megagauss results. In the magnetic field range 0 rarrplusmn0.5 T, however, a well detectable anomaly in the transmission is observed, which cannot be explained by the Drude concept. To corroborate that the observed magnetic-field dependent structures in the experimental data originate from the HgSe:Fe-quantum dots, experiments without any sample and also with samples with the same substrate but without any quantum dots were performed. In these experiments no anomaly was observed. We suggest and discuss the observed structure as the result of a change of the effective carrier concentration due to Fe⁺⁺/Fe⁺⁺⁺ electron fluctuation as well as due to "magneto condensation". Our experiments demonstrate again the universal applicability of FIR-radiation for the investigation of electronic systems in solids, especially in complex semiconductor nano-structures.