Cyclotron resonance photoconductivity of a two-dimensional electron gas in HgTe quantum wells

Far-infrared cyclotron resonance photoconductivity (CRP) is investigated in HgTe quantum wells (QWs) of various widths grown on (013) oriented GaAs substrates. It is shown that CRP is caused by the heating of two-dimensional electron gas (2DEG). From the resonance magnetic field strength effective masses and their dependence on the carrier concentration is obtained. We found that the effective mass in each sample slightly increases from the value (0.0260 \pm 0.0005)m_0 at N_s = 2.2x10^11 cm^(-2) to (0.0335 \pm 0.0005)m_0 at N_s = 9.6x10^11 cm^(-2). Compared to determination of effective masses by the temperature dependence of magnitudes of the Shubnikov-de Haas (SdH) oscillations used so far in this material our measurements demonstrate that the CRP provides a more accurate (about few percents) tool. Combining optical methods with transport measurements we found that the transport time substantially exceeds the cyclotron resonance lifetime as well as the quantum lifetime which is the shortest.Comment: 3 pages, 2 figure

Seasonality of isotopic and chemical species and biomass burning signals remaining in wet snow in the accumulation area of Sofiyskiy Glacier, Russian Altai Mountains

Preliminary glaciological investigation was carried out on the accumulation area of Sofiyskiy Glacier, Russian Altai Mountains in July 2000. Analyses of a 12.3m core and 3m deep pit samples show that seasonal variations of δ^O, tritium and melt features remained in the wet snow layers. Annual layer thickness determined on the basis of seasonality of these elements for 12.3m core is 0.99m of water on average in 1994-1999 with a minimum in 1998 when the minimum mass balance was observed for three other glaciers in the Altai Mountains. High correlations of NH_4^+ concentration with concentrations of K^+, SO_4^2, NO_3^- and PO_4^ are found. NH_4^+ and K^+ are considered to be of biomass burning origin, and PO_4^ and NH_4^+ are due to chemical ingredients used for fire extinction in biomass burning

Admittance of MIS structures based on graded-gap MBE HgCdTe with Al2O3 insulator

The paper presents the results of studies of the admittance of MIS structures based on heteroepitaxial MBE n (p)-Hg0.78Cd0.22Te with insulator coating SiO2/Si3N4 and Al2O3 in the test signal frequency range 10 kHz-1 MHz at temperatures ranging from 8 to 220 K. The main parameters of MIS structures with different insulators were determined. MIS structures with Al2O3 have a large enough insulator capacitance (compared to SiO2/Si3N4), a significant modulation capacitance on the CV characteristics, high dielectric strength and low values of the flat-band voltage. The effective charge density found from the value of the flat-band voltage and slow interface trap density for structures with Al2O3 comparable with the corresponding densities for structures with SiO2/Si3N4

Impact of the graded-gap layer on the admittance of MIS structures based on MBE-grown n-Hg1-xCdxTe (x = 0.22-0.23) with the Al2O3 insulator

The impact of the presence of the near-surface graded-gap layers with an increased content of CdTe on the admittance of MIS structures based on MBE-grown n-Hg1–xCdxTe (x = 0.22–0.23) with the Al2O3 insulating coating has been experimentally studied. It has been shown that the structures with a gradedgap layer are characterized by a deeper and wider capacitance dip in the low-frequency capacitance–voltage (CV) characteristic and by higher values of the differential resistance of the space-charge region than the structures without such a layer. It has been found that the main features of the hysteresis of capacitance dependences typical of the graded-gap structures with SiO2/Si3N4 are also characteristic of the MIS structures with the Al2O3 insulator. The factors that cause an increase in the CV characteristic hysteresis upon formation of the graded-gap layer in structures with SiO2/Si3N4 or Al2O3 are still debatable, although it may be assumed that oxygen plays a certain role in formation of this hysteresis

Exploring the effects of a one-dimensional periodic potential on a three-dimensional topological insulator

High mobility two-dimensional systems with superposed 1D lateral periodic potentials exhibit characteristic commensurability (Weiss) oscillations that reflect the interplay of the cyclotron radius at the Fermi level and the superlattice period. Here, we impose a one-dimensional periodic potential on strained HgTe, which is a strong 3D topological insulator. By tuning the Fermi level with top gates, the effects of the artificial potential can be studied in the bulk gap, where only Dirac surface states exist, in the conduction band, and in the valence band, where Dirac electrons and holes coexist. On the electron side, we observe clear commensurability oscillations whose period is governed by the carrier density of the top-surface Dirac electrons. Unexpectedly, weak commensurability oscillations are also observed in the valence band with a period that depends on both electron and hole density

Unipolar barrier structures based on HgCdTe for infrared detection

One of the topical areas of solid state photoelectronics is the creation of infrared detectors based on unipolar barrier systems (for example, with an nBn architecture). The greatest progress has been achieved in the development of barrier detectors based on semiconductors of the AIIIBV group, which is associated with the possibility of realizing systems with a zero barrier in the valence band. Unipolar barrier detectors based on mercury cadmium telluride (HgCdTe) grown by molecular beam epitaxy (MBE) are of interest due to significant technological advantages, since the creation of such devices can abandon the defect forming procedure of ion implantation. Despite a significant number of theoretical works, only a few attempts are known to practically implement nBn detectors based on MBE HgCdTe

An experimental study of the dynamic resistance in surface leakage limited nBn structures based on HgCdTe grown by molecular beam epitaxy

Mid-wave infrared nBn structures based on HgCdTe grown by molecular beam epitaxy on GaAs (013) substrates were fabricated. The composition in the absorbing layer was 0.29, and in the barrier layer it was 0.67. It was shown that the dark currents of the created nBn structures are limited by the surface leakage component. To study the bulk component of the dark current, it was proposed to use the admittance measurements of test metal-insulator-semiconductor (MIS) devices based on fabricated nBn structures in the case of the formation of a backward contact to the absorbing layer. It was established that surface leakage does not afect the dynamic resistance of the MIS device barrier. The dependence of the dynamic resistance of the barrier layer (Rb) of the MIS device in the accumulation mode on the area of the front electrode (A), voltage, and temperature was determined. It was shown that, with the exclusion of surface leakage, the values of the RbA product in a temperature range of 230–300 K at forward biases are determined by the difusion current of holes from the contact layer, and at reverse biases, by the difusion current from the absorbing layer. It was found that at temperatures of 210–300 K, RbA values exceeding the values of this parameter determined according to the empirical model Rule 07 were realized in the fabricated structures