The results of plasma reflection investigations in p-HgTe are described. It is shown, that the plasma reflection spectrum shift towards small energies and the decrease of their depths with increasing temperature cannot be explained by the dielectric anomaly of the zero gap semiconductor due to the rS -rS transition only. The analysis of the experimental results shows that the optical effective mass value has both, a temperature and concentration dependence. Such a dependence may be explained in the frame of the Kane theory, if the renormalization of the energy spectrum of holes due to exchange electron-electron interaction is taken into account.
a), and V. I. IVANOV-OMSKII (b)Recently the microwave technique for simultaneous measurement of some carrier parameters in semiconductors and semimetals was described (1). We report here the application of this method to HgTe which is a zero energy gap crystal. It was possible t o observe the non-resonant cyclotron absorption, a helicon interference structure, and the Shubnikov-de-Haas microwav? oscillations.The magnetic field derivative of the reflection signal (dR/dB) was measured using circulary polarized 37.2 GHz microwaves at liquid helium temperatures. Samples of HgTe with conductivity about 200 h'cm- ' and Hall coefficient about 3200 cm /C (measured in a field of 100 G) at 4.2 K were used in our experiments. 3 0 Fig. 1 shows a typical dR/dB trace at 4.2 OK. The first maximum corresponds to the non-resonant cyclotron absorption and subsequent ones have their origin in the Fabri-Perrot type interference of the helicons. The positions of the first peak and characteristic points of the interference picture enable us to estimate the carrier density, N, the electron effective mass, m*, and the low frequency dielectric constant, by following the method described in (1). The experimental data handling by the least squares method gives the follow-EL' 15 ing sample parameters: N = 1 . 8~1 0 E. % 100 to 200. The resulting concentration agrees well with its Hall coefficient: within the limits of experimental e r r o r our effective mass estimate coincides with the value obtained earlier (2), but that for the dielectric constant differs essentially from those reported by others (3). This discrepancy decreases as the temperature increases. cm 3; m* = (0.030 2 0.005) mo, and LIt is believed that a reason of the discrepancy lies in the anomalous behaviour
GELMONT (a), V. I. IVANOV-OMSKII (a), and E. N. UERAINTSEV (b)It is shown that in gapless semiconductors in a magnetic field the transmission of electromagnetic waves is possible at frequencies less than the plasma frequency even in the Voigt geometry. This is due to the combined resonance between two sets of Landau levels.
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