Recently the hole effective mass has been determined from plasma edge measurements in mercury telluride at 95 and 300 OK (1). The hole effective mass was found to increase with decreasing temperature, but to be independent of hole density within the limits of experimental error.In the present note some new experimental results on plasma reflection at lower temperature and higher concentration of holes are reported. These results reveal a complicated temperature dependence of the hole effective mass in HgTe.The measurements of the reflectivity were made at 7, 95, and 300 OK: there were no important changes in the experimental method described in (1). Fig. 1 shows the reflection spectra near the plasma edge of p-HgTe with a hole density of 2. lXr019 ~m -~. One can see that the depth of the reflectivity minimum increases as the temperature decreases, while the shift of the minimum is a non-monotonous function of temperature.The observed peculiarity can be a consequence of a change in effective mass or dielectric permeability. But Sniadower (2) has shown that the dielectric permeability of HgTe is a smooth function of temperature. Thus the peculiarity of the temperature shift of the plasma edge is more likely associated with a non-monotonous change in the effective mass. The behaviour of plasma edge with temperature is rather similar for samples with other densities of holes.The results of plasma reflection measurements were used to estimate the hole effective mass by methods outlined earlier (1). The temperature dependence of the effective mass is shown in Fig. 2 for two samples with different densities of holes.The distinctive feature of the temperature dependence is the existence of a maximum
The detection of cyclotron absorption by change in static conductivity is a sensitive method for many semiconductors. The high sensitivity of this method allows to detect the cyclotron absorption at low temperatures T when the thermal energy kT is much smaller than the ionization energy of shallow impurities and the free electron concentration is too small.By applying shallow impurity break-down electric fields, the free electron concentration drastically increases and it causes some interesting physical effects concerning the CR line shape (linewidth and its position). The influence of free electrons on the CR line shape is different at high and low magnetic fields. At high magnetic fields l c % a i (lc magnetic length, < effective Bohr radius) we observed a positive shift (A B > 0) of the CR line in n-GaAs in break-down electric fields / l / . This effect was believed to be caused by the influence of free electrons screening on the value of the potential fluctuation.At low magnetic fields the influence of free electrons on the CR line shape is mainly due to the plasma shift towards &he low magnetic field direction which increases with decreasing magnetic field.In this letter we report the results of plasma shift investigations of the CR line in n-GaAs. CR measurements were carried out at liquid helium temperature using a laser magnetic spectrometer at fixed radiation wavelength A. = 337 p m of a continuous HCH laser. The change of static conductivity of the specimen under radiation was recorded a s a function of magnetic field.Epitaxial n-GaAs layers with ND = 1 0 to 1 0 cm , k = N /N = 0.35 to 0.65, p77 = (10 to 5.7)xlO cm V were used. The measurements were carried out in Voigt geometry with 3 1 H. The temperaturerise is estimated to be less than 0 . 1 K even for the strongest electric fields used in experiments.
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.
The effect of γ‐irradiation (1.25 MeV; 4.94 × 108 Rad) on the photoelectrical and electrical properties of volume samples of gallium selenide and Sb—GaSe barrier structures is investigated. Irradiation of volume samples is shown to reduce the resistivity along the C‐axis and to give rise to a new energy level Ev + 0.21 eV. The defects of γ‐irradiation, identified with the complexes of point defects, are annealed at temperatures about 500 K with the annealing activation energy 0.71 eV. Sb—GaSe barrier structures are found to be photosensitive Isc ≈ 1 mA/cm2, Voc ≈ 0.6 V under light illumination ≈ 100 mW/cm2. γ‐irradiation‐induced variation in the spectral distribution of photoconductivity, current—voltage and current—capacity characteristics depend on the fact whether the whole of Sb—GaSe structure (a‐type structure) or only gallium selenide substrate (b‐type structure) is being subjected to irradiation. The difference in the variation of the characteristics of a‐ and b‐structures is attributed to the effect of the irradiation‐stimulated diffusion in a‐type structures, which gives rise to local levels in the boundary region. The obtained experimental data are used to construct the band energy diagram of Sb—GaSe barrier structure, explaining the observed variations in the electrical and photoelectrical characteristics at γ‐irradiation.
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