N. N. Mikhailov

Observation of three-dimensional massless Kane fermions in a zinc-blende crystal

Graphene and topological-insulator surfaces are well known for their two-dimensional conic electronic dispersion relation. Now three-dimensional hyperconic dispersion is shown for electrons in a HgCdTe crystal—once again bridging solid-state physics and quantum electrodynamics.M. Orlita, 2, ∗ D. M. Basko, M. S. Zholudev, 5 F. Teppe, W. Knap, V. I. Gavrilenko, N. N. Mikhailov, S. A. Dvoretskii, P. Neugebauer, C. Faugeras, A.-L. Barra, G. Martinez, and M. Potemski Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, Grenoble, France Charles University, Faculty of Mathematics and Physics, Ke Karlovu 5, 121 16 Praha 2, Czech Republic Université Grenoble 1/CNRS, LPMMC UMR 5493, B.P. 166, 38042 Grenoble, France Laboratoire Charles Coulomb (L2C), UMR CNRS 5221, GIS-TERALAB, Université Montpellier II, 34095 Montpellier, France Institute for Physics of Microstructures, RAS, Nizhny Novgorod, Russia A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany

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 ± 0.0005)m0 at Ns = 2.2⋅10 cm to (0.0335 ± 0.0005)m0 at Ns = 9.6⋅10 cm. 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. PACS: 73.21.Fg; 73.63.Hs; 73.50.Pz; 76.40.+b

Molecular beam epitaxy of high quality Hg1 − xCdxTe films with control of the composition distribution

Abstract An investigation of Hg 1 − x Cd x The heterostructure (MCT HS) growth processes using in situ ellipsometry by molecular beam epitaxy (MBE) was carried out. High quality MCT HS with a low density of V-shaped defects (near 10 2 cm −2 ) were grown on (103) GaAs substrates. Electron probe micro analysis (EPMA) revealed the presence of elemental tellurium inside the V-shaped defects. The appearance of V-shaped defects was connected with processes in which tellurium molecules take part on the growing surface. The MCT HS with wide band gap layers at the interface with the substrate and at the surface had the best electrical characteristics. In as-grown n-type material the electron concentrations, mobilities and life time of the minority carriers were 2 × 10 14 –5 × 10 15 cm −3 , 50000–350000 cm 2 /V · s, and up to 10 −6 s, respectively. In as-grown p-type material the hole concentrations, mobilities and life time of the minority carriers were 5 × 10 15 –2 × 10 16 cm −3 , over 500 cm 2 /V · s, and over 10 −7 s, respectively. Photoconductors and photodiodes were fabricated on the base of MCT HS with good photoelectrical parameters.

Two-dimensional electron-hole system in a HgTe-based quantum well

A two-dimensional electron-hole system consisting of light high-mobility electrons with a density of Ns = (4–7) × 1010 cm−2 and a mobility of μn = (4–6) × 105 cm2/V s and heavier low-mobility holes with a density of Ps = (0.7–1.6) × 1011 cm−2 and a mobility of μp = (3–7) × 104 cm2/V s has been discovered in a quantum well based on mercury telluride with the (013) surface orientation. The system exhibits a number of specific magnetotransport properties in both the classical magnetotransport (positive magnetoresistance and alternating Hall effect) and the quantum Hall effect regime. These properties are associated with the coexistence of two-dimensional electrons and holes.

Cyclotron resonance and interband optical transitions in HgTe/CdTe(0 1 3) quantum well heterostructures

Cyclotron resonance spectra of 2D electrons in HgTe/CdxHg1−xTe (0 1 3) quantum well (QW) heterostructures with inverted band structure have been thoroughly studied in quasiclassical magnetic fields versus the electron concentration varied using the persistent photoconductivity effect. The cyclotron mass is shown to increase with QW width in contrast to QWs with normal band structure. The measured values of cyclotron mass are shown to be systematically less than those calculated using the 8 × 8 Kane model with conventional set of HgTe and CdTe material parameters. In quantizing pulsed magnetic fields (Landau level filling factor less than unity) up to 45 T, both intraband (CR) and interband magnetoabsorption have been studied at radiation wavelengths 14.8 and 11.4 µm for the first time. The results obtained are compared with the allowed transition energies between Landau levels in the valence and conduction bands calculated within the same model, the calculated energies being again systematically less (by 3–14%) than the observed optical transition energies.

Molecular-beam epitaxy of mercury-cadmium-telluride solid solutions on alternative substrates

Growth processes were considered for heteroepitaxial structures based on a mercury-cadmium-telluride (MCT) solid solution deposited on GaAs and Si alternative substrates by molecular-beam epitaxy. Physical and chemical processes of growth and defect-generation mechanisms were studied for CdZnTe epitaxy on atomically clean singular and vicinal surfaces of gallium-arsenide substrates and CdHgTe films on CdZnTe/GaAs surfaces. ZnTe single-crystalline films were grown on silicon substrates. Methods for reducing the content of defects in CdZnTe/GaAs and CdHgTe films were developed. Equipment for molecular-beam epitaxy was designed for growing the heteroepitaxial structures on large-diameter substrates with a highly uniform composition over the area and their control in situ. Heteroepitaxial MCT layers with excellent electrical parameters were grown on GaAs by molecular-beam epitaxy.

Peculiarities of the MBE growth physics and technology of narrow-gap II–VI compounds

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. Experimental research and a crystallochemical consideration of the chemical interaction of the film and substrate components in the A 2 B 6 /GaAs heterostructure were carried out. It was found that surface faceting, twinning and breaking of stoichiometry of the growing structure can be explained by the excess of valent electrons at the A 2 B 6 /GaAs interface. The films were grown in a multichamber mercury cadmium telluride (MCT) MBE system with different compositions of the residual gas phase in different chambers. The MCT growth chamber is equipped with a system of molecular sources of original design and a built-in automatic ellipsometer. The used system of sources allows for growing MCT films without sample rotation, uniform in composition over the substrate area of 51 mm in diameter (the composition gradient does not exceed 0.002 cm −1 ). Because there is no substrate rotation, continuous measurements of film composition can be performed during growth, and structures with specified composition over thickness can be grown. The introduction of layers with a varying energy gap into the heteroepitaxial structure increases the carriers lifetime up to 2 μs for x=0.22 (77 K). A model of defects, determining the electric parameters of MBE grown films in the presence of gallium sources, is suggested. Linear photoconductor arrays for the 8-12 μm band with background limited parameters were fabricated from the grown MCT films.

Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements, respectively, utilize the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods we propose is an easy to handle all-electric approach, which is demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.

Study of lifetimes and photoconductivity relaxation in heterostructures with HgxCd1 − xTe/CdyHg1 − yTe quantum wells

Carrier lifetimes in the continuum of the quantum well of a HgxCd1 − xTe/CdyHg1 − yTe hetero-structure were studied by terahertz pump-probe spectroscopy. It is found that the relaxation duration of the transmission signal is ∼65 ps and is independent of the pump power. Such rapid relaxation in these structures is most likely determined by the interaction of holes with acoustic phonons due to a high density of states in the valence band and a larger effective mass compared with electrons. By the obtained data, the times of the interband nonradiative recombination of holes are determined. In this publication, we report the results of numerical calculation of the energy spectrum of the model structure, in which the possibility of obtaining population inversion at specified concentrations of nonequilibrium carriers is analyzed.

Transport properties of a 3D topological insulator based on a strained high mobility HgTe film

We investigate the magnetotransport properties of strained 80 nm thick HgTe layers featuring a high mobility of μ ∼ 4 × 10(5) cm(2)/V · s. By means of a top gate, the Fermi energy is tuned from the valence band through the Dirac-type surface states into the conduction band. Magnetotransport measurements allow us to disentangle the different contributions of conduction band electrons, holes, and Dirac electrons to the conductivity. The results are in line with previous claims that strained HgTe is a topological insulator with a bulk gap of ≈ 15 meV and gapless surface states.