Te Heterostructures Research Articles

Molecular Beam Epitaxy of Homogeneous Topological HgTe on Doped InAs Substrate

AbstractHgTe has been considered to be one of the most versatile topological materials. Depending on the in‐plane strain, Weyl and Dirac semi‐metal, as well as topological insulator phases, are feasible. Here, for the first time it is reported, that an InAs:S substrate promotes an initial 2D growth of a ZnTe thin layer and subsequent high crystalline quality ZnTe/CdTe superlattices serve as a smooth and continuous virtual substrate for the growth of (Cd,Hg)Te/HgTe/(Cd,Hg)Te heterostructures with unstrained quantum well HgTe (topological insulator) and compressively strained bulk HgTe (Weyl semimetal) by molecular beam epitaxy. Compared with the superlattices previously grown on GaAs substrates, the quantum well and bulk heterostructures exhibit homogeneous surfaces with root mean square roughnesses of 0.88–0.93 nm, which is three times lower than those observed for 3D islands (2.7–3.4 nm) on GaAs substrates. Additionally, magnetotransport measurements confirm high electronic quality and demonstrate that the S‐doped InAs substrate can be used as an effective back gate. These results manifest a (big) step forward toward the improvement of micro‐ and nanometer‐sized top‐ and back‐gated device fabrication on topological materials.

High-Performance 1D CdS/2D Te Heterojunction Photodetector

Abstract Van der Waals heterostructures facilitate the versatile combination of two-dimensional (2D) materials with semiconductors that possess distinctive band structures, offering a promising platform for developing photodetectors with extensive spectral range and high sensitivity. This study showcases the flawless integration of one-dimensional (1D) CdS nanowires with 2D Te nanosheets, resulting in the creation of a high-performance, mixed-dimensional heterojunction photodetector. Bandgap engineering at the CdS/Te interface promotes Type II band alignment, markedly improving the separation and transport of photo-generated charge carriers. Additionally, the interaction between materials of different dimensions significantly enhances the device’s photoresponsivity and detectivity. When operated at low bias, the photodetector displays an impressive rectification ratio of up to 8.57×103, along with superior photoelectric performance spanning the ultraviolet to visible light spectrum. Particularly under 450 nm wavelength laser illumination, the device displayed a high photoresponsivity of up to 126 A W−1, a high detectivity of 1.03×1010 Jones, an external quantum efficiency of up to 3.49×102%, and a rapid response time of 35 ms. The photoresponsivity of this device was at least an order of magnitude higher than other reported mixed-dimensional heterojunction photodetectors. The development of the 1D CdS/2D Te heterostructure opens new pathways for high-sensitivity, broad-spectrum photodetection technologies.

High-Performance and Polarization-Sensitive Imaging Photodetector Based on WS2 /Te Tunneling Heterostructure.

Next-generation imaging systems require photodetectors with high sensitivity, polarization sensitivity, miniaturization, and integration. By virtue of their intriguing attributes, emerging 2D materials offer innovative avenues to meet these requirements. However, the current performance of 2Dphotodetectors is stillbelow the requirements forpractical application owing to the severe interfacial recombination, the lack of photoconductive gain, and insufficient photocarrier collection. Here, a tunneling dominant imaging photodetector based on WS2 /Te heterostructure is reported. This device demonstrates competitive performance, including a remarkable responsivity of 402 A W-1 , an outstanding detectivity of 9.28 × 1013 Jones, a fast rise/decay time of 1.7/3.2ms, and a high photocurrent anisotropic ratio of 2.5. These outstanding performances can be attributed to the type-I band alignment with carrier transmission barriers and photoinduced tunneling mechanism, allowing reduced interfacial trapping effect, effective photoconductive gains, and anisotropic collection of photocarriers. Significantly, the constructed photodetector is successfully integrated into a polarized light imaging system and an ultra-weak light imaging system to illustrate the imaging capability. These results suggest the promising application prospect of the device in future imaging systems.

Magnetotransport in Graphene/Pb0.24Sn0.76Te Heterostructures: Finding a Way to Avoid Catastrophe.

While heterostructures are ubiquitous tools enabling new physics and device functionalities, the palette of available materials has never been richer. Combinations of two emerging material classes, two-dimensional materials and topological materials, are particularly promising because of the wide range of possible permutations that are easily accessible. Individually, both graphene and Pb1-xSnxTe (PST) are widely investigated for spintronic applications because graphene's high carrier mobility and PST's topologically protected surface states are attractive platforms for spin transport. Here, we combine monolayer graphene with PST and demonstrate a hybrid system with properties enhanced relative to the constituent parts. Using magnetotransport measurements, we find carrier mobilities up to 20 000 cm2/(V s) and a magnetoresistance approaching 100%, greater than either material prior to stacking. We also establish that there are two distinct transport channels and determine a lower bound on the spin relaxation time of 4.5 ps. The results can be explained using the polar catastrophe model, whereby a high mobility interface state results from a reconfiguration of charge due to a polar/nonpolar interface interaction. Our results suggest that proximity induced interface states with hybrid properties can be added to the still growing list of behaviors in these materials.

Shape-Controllable Tellurium-Driven Heterostructures with Activated Robust Immunomodulatory Potential for Highly Efficient Radiophotothermal Therapy of Colon Cancer.

Tellurium (Te)-based semiconductor easily leads to the recombination of photogenerated electron-hole pairs (h+-e-) that severely limits the efficiency of reactive oxygen species (ROS) generation and further hinders its clinical application in biomedicine. With regard to these problems, herein we designed and synthesized a Te heterostructure (BTe-Pd-Au) by incorporating palladium (Pd) and gold (Au) elements to promote its radiosensitivity and photothermal performance, thus realizing highly efficient radiophotothermal tumor elimination by activating robust immunomodulatory potential. This shape-controllable heterostructure that coated by Pd on the surface of Te nanorods and Au in the center of Te nanorods was simply synthesized by using in situ synthesis method, which could promote the generation and separation of h+-e- pairs, thereby exhibiting superior ROS producing ability and photothermal conversion efficiency. Using a mouse model of colon cancer, we proved that BTe-Pd-Au-R-combined radiophotothermal therapy not only eradicated tumor but also elicited to a series of antitumor immune responses by enhancing the cytotoxic T lymphocytes, triggering dendritic cells maturation, and decreasing the percentage of M2 tumor-associated macrophages. In summary, our study highlights a facile strategy to design Te-driven heterostructure with versatile performance in radiosensitization, photothermal therapy, and immunomodulation and offers great promise for clinical translational treatment of colon cancer.

One-pot synthesis of dumbbell shaped PbS–Te hybrids with promising photothermal properties

The development of multi-component photothermal agents has attracted increasing attention due to their potential applications in energy conversion, medical treatments, etc. Herein, a dumbbell shaped PbS–Te heterostructure was prepared via a one-pot microwave-assisted decomposition of lead dimethyl dithiocarbamate and tellurium diethyl dithiocarbamate. The as-obtained PbS–Te hybrids exhibit excellent photothermal stability and strong optical absorption over a broad wavelength range spanning from ultraviolet to near-infrared, where the photothermal conversion efficiency could reach as high as 12.1%. Such promising photothermal performance demonstrates the advantages of one-pot synthesis that results in more intimate contacts among individual components.

Emission of Light by CdMnTe/CdMgTe Heterostructure with Narrow Quantum Wells

The optical properties of the Cd0.4Mn0.4Te/Cd0.5Mg0.5Te heterostructure with quantum wells of 7 monolayers in thickness are studied. The temperature dependences of the integral intensity of luminescence of the barrier layer and quantum well and intracenter luminescence of manganese ions are determined, and the luminescence excitation spectra are measured. Numerous components corresponding to LO phonons of the CdTe, MgTe, and MnTe types are observed in the Raman scattering spectra.

Излучение света гетероструктурой CdMnTe/CdMgTe с узкими квантовыми ямами

AbstractThe optical properties of the Cd_0.4Mn_0.4Te/Cd_0.5Mg_0.5Te heterostructure with quantum wells of 7 monolayers in thickness are studied. The temperature dependences of the integral intensity of luminescence of the barrier layer and quantum well and intracenter luminescence of manganese ions are determined, and the luminescence excitation spectra are measured. Numerous components corresponding to LO phonons of the CdTe, MgTe, and MnTe types are observed in the Raman scattering spectra.

High Magnetic Field Facility for Cyclotron Resonance Investigation in Semiconductors

In this paper, a compact high magnetic field facility for cyclotron resonance (CR) investigation in the mid-infrared range is presented. A technology of multiturn coils winding with microcomposite Cu–Nb wire was developed in the Sarov Physics and Technology Institute Norwegian University of Science and Technology Moscow Engineering Physics Institute for the fabrication of compact nondestructive solenoids up to 50 T. An optical scheme and details of experimental techniques of CR measurements are discussed. Two peaks of magnetic absorption at 28 THz were observed in a narrow-gap HgTe/Hg1– x Cd x Te heterostructures with quantum wells at 80 K.

Synthesis of Tellurium Heterostructures by Galvanic Displacement Reaction of Zinc in Alkaline Baths

Tellurium (Te) nanostructures, including nanowires and branched nanorods, were synthesized by galvanic displacement reaction (GDR) of zinc foils in alkaline baths containing TeO32− ions. The dimension, morphology, and crystal structure of the Te nanostructures were controlled by varying the electrolyte composition, pH, and the reaction temperature. For examples, single crystalline Te nanowires were synthesized at low TeO32− concentrations (e.g., 2 mM), whereas 3-D branched nanorods were obtained at higher TeO32− concentrations (e.g., >10 mM) at a fixed pH of 13.1. The diameter of the branches was increased by increasing TeO32− concentration. Solution pH also effected the morphology of Te heterostructures where the pH range from 12.8 to 13.1 yielded branched nanorods whereas higher pH (i.e., 14.7) yielded nanowires at a fixed TeO32− concentration (i.e., 10 mM). Reaction temperature predominately effected on the dimension where the average diameter increased from 49 nm to 200 nm with increasing temperature from 4 °C to 50 °C. Various electrochemical analytical methods including open circuit potential (OCP), linear sweep voltammograms (LSVs) as well as linear potentiodynamic polarizations (LPs) were carried out to understand the underlying reaction mechanism. Based on these analysis, the formation of branched nanorods was attributed to secondary nucleation at the crystal imperfections.

Observation of thermal-misfit strain relaxation in a PbTe semiconductor grown on Cd0.96Zn0.04Te(1 1 1)

The thermal-misfit strain relaxation in epitaxial PbTe grown on Cd0.96Zn0.04Te(1 1 1) substrates has been studied by the combined characterization of atomic force microscopy and high-resolution transmission electron microscopy. It is shown that the strain relaxes by the movement of dislocations in the ⟨1 1 0⟩–{1 0 0} primary glide system and leaves straight slip steps on the surface. The thermal-misfit strain relaxation is greatly affected by the growth temperature and post-growth cooling rate. Post-growth treatment with a slower cooling rate improves the crystalline quality of PbTe grown on Cd0.96Zn0.04Te(1 1 1). Because of the easy dislocation glide down to the interface in the ⟨1 1 0⟩–{1 0 0} primary glide system, PbTe/Cd0.96Zn0.04Te(1 1 1) heterostructures exhibit good crystal and optical qualities, which indicate that PbTe/CdZnTe heterostructures may become a promising candidate for the fabrication of PbTe-based mid-infrared optoelectronic devices.

Spin filtering through Cd 1−yMg yTe/Cd 1−xMn xTe heterostructure

The spin filtering through Cd 1− y Mg y Te/Cd 1− x Mn x Te heterostructure, both with zero and with positive zero-field conduction band offset, is investigated theoretically. The magnetic field dependence of the transmission coefficients, current densities, and spin polarizations for considered systems have been studied. It is found that a positive zero-field conduction band offset as high as 3 meV shifts considerably the onset of the spin-up complete suppression to lower magnetic field region and thereby unity spin polarization initiates at lower magnetic field.

Nanoindentation as a Tool for Formation of Thin Film-Based Barrier Structures

AbstractA2B6 semiconductors and their solid solutions (ZnSe, ZnTe, CdTe, ZnCdHgTe) are matter of choice for near- and far-infrared optoelectronics. The importance of maximally reduced degree of defectness for these materials is not subjected to discussion. However, preparation of high quality barrier structures based on these compounds by means of MBE, laser technology or liquid phase technique is not always successful due to lattice parameters mismatch. At the same time, good selection of a proper buffer layer may also pose some unavoidable problems. From this point of view the nanoindentation as a tool of defect engineering can be effective for fabrication of surface barrier structures. The first experimental results and numerical simulation of experimental data obtained under investigation of nanoindentation effect on electric characteristics (in particular, current – voltage (I-V) and capacitance – voltage (C-V)) of ZnCdHgTe thin films and ZnCdHgTe/Cd(Zn)Te heterostructures at the room temperature are presented.

Infrared photoluminescence imaging of infrared materials: HgCdTe/Cd(Zn)Te heterostructures

We demonstrate the application of infrared photoluminescence (IRPL) imaging technique for the structural studies of infrared materials such as HgCdTe/Cd(Zn)Te heterostructures grown by liquid phase epitaxy (LPE). The two-dimensional IRPL maps were recorded in the near-infrared range at fixed wavelengths corresponded to the maximums of Cd(Zn)Te PL emission bands. The results of IRPL imaging studies were compared with the structure characterization data of HgCdTe/Cd(Zn)Te heterostructures, which were obtained by X-ray imaging techniques (in particular, synchrotron white beam back reflection topography).

Mixing of impurity levels by a built‐in electric field in a CdMgTe/CdZnTe heterostructure

Magneto-optical studies were performed on a Cd0.88Mg0.12Te/Cd0.97Zn0.03Te heterostructure in which the CdMgTe barrier was δ-doped with iodine donors and the CdZnTe channel was δ-doped with nitrogen acceptors. The photoluminescence spectrum was dominated by a line with an energy close to that of the CdMgTe barrier which is interpreted as a result of donor–acceptor transitions. Stokes parameters polarisation spectroscopy showed that the line was purely circularly but very weakly polarised (8% in 6 T). It was proposed that this weak degree of polarisation comes from mixing of impurity levels by a strong electric field present in the investigated structure.

Ising quantum Hall ferromagnet in magnetically doped quantum wells.

We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T(C) as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance "spikes" at T-->T(C) corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.

MBE growth and characterization of Hg based compounds and heterostructures

The MBE growth of Hg 1− x Cd x Te alloys and type III HgTe/Hg 1− x Cd x Te heterostructures has been discussed, including similarities and differences between the (0 0 1) and (1 1 2)B orientations. Furthermore the MBE growth of HgTe based quantum wells (QWs) with the incorporation of Mn are additional topics. An investigation of the optical properties of type III superlattices with a normal band structure has lead to information about band structure of these heterostructures as well as information about the interface and the semimetallic QW. For example, by means of the full 8×8 Kane Hamiltonian in the envelope function approximation, it has been demonstrated that the energy separation between the H1–E1 and L1–E1 intersubband transition energies is primarily determined by the valence band offset, Λ, between HgTe and CdTe. This has led to unambiguous values for the offset and its temperature dependence, i.e. Λ( T)=570±60 meV and dΛ/d T=−0.40±0.04T meV/K. Furthermore the energy gap of HgTe at room temperature has also been determined. Magneto-transport measurements of n-type QWs show very pronounced Shubnikov-de Haas (SdH) oscillations and well developed quantum Hall plateaus for temperatures up to approximately 60 K. A large Rashba spin–orbit splitting of the first conduction subband, H1, has been observed in HgTe/Hg 1− x Cd x Te QWs with an inverted band structure. Self-consistent Hartree calculations of the band structure based on the above model allows us to quantitatively describe the experimental results and demonstrates that the heavy hole nature of the H1 subband greatly influences the spatial distribution of electrons in the QW and thus enhances the Rashba spin splitting, i.e. Δ E H1= βk ∥ 3. Furthermore, the presence of two periodic SdH oscillations in p-type QWs with an inverted band structure has been observed and is the first direct evidence that these heterostructures are indirect semiconductors. The influence of Mn in the upper barrier on the 2D electrons in the well has been investigated as a function of their separation. With spacer thicknesses of 10 and 15 nm, no appreciable change is observed, however, a reduction of the spacer thickness to 5 nm results in an increase in the maximum population difference between the two Rashba spin split H1 subbands by a factor of approximately two.

Properties of HgCdTe crystals passivated by A 2B 6 layers

The effect of A 2B 6 passivating layers on properties of bulk p-Hg 1− x Cd x Te crystals has been studied. CdTe, ZnTe and CdS layers with 400 nm thickness were grown on the surface of a sample by a pulse laser deposition (PLD) method. The galvanomagnetic and photoelectric properties of the passivated crystals were measured. Accordingly, the layers have only a weak influence on the properties of the crystals. The electrical properties of the related Al–CdTe–Hg 0.8Cd 0.2Te and Al–CdS–Hg 0.8Cd 0.2Te heterostructures obtained by PLD method have been studied too.

Radiation resistance of GaAs–AlGaAs heterostructures doped with isovalent and rare-earth elements

When GaAs–Si and GaAs–AlGaAs heterostructures are exposed to γ-quanta, radiation stimulated ordering is observed. However, the gettering efficiency in such systems falls for layer widths more than 1 μm. For this reason we seek effective methods of radiation resistance improvement of materials in which one would expect point radiation defects to be gettered not only at defect boundaries, but also in the active layer volume. S.i.GaAs–s.i.Al x Ga 1− x As– nGaAs : Te heterostructures are presented with epitaxial layers (doped with Yb or undoped), obtained by means of LPE (liquid-phase epitaxy). The electron concentration in nGaAs was found to be (1–3)×10 18 cm −3 for widths 1–3 μm. The samples were exposed to 60Co γ-quanta with doses of 10 5–10 7 rad. Investigations of irradiated samples by means of low-temperature (4.2 K) photoluminescence have shown considerable decrease of exciton halfwidth in the boundary spectra of nGaAs : Te : Yb epitaxial layers in comparison with nGaAs : Te layer spectra. This is caused by background impurity gettering which happens on the s.i.Al x Ga 1− x As– nGaAs heteroboundaries as well as in deformed regions in the epitaxial layer volume. Formation of such regions is caused by the difference between the covalent radii of Yb atoms and GaAs lattice atoms. The maximum effect of radiation stimulated gettering of dopants in nGaAs epitaxial layers is observed for Yb concentrations which are equal to 10 −4–10 −5 atomic fractions in a solution-melt. It is determined that the deformed regions in epitaxial layer volumes and heteroboundaries could be efficient drains for point radiation defects which form under radiation exposure. The investigations carried out showed that the doping of an epitaxial layers by rare-earth impurities provides considerable improvement in forming radiation resistant III–V materials.

Pressure Effect on Parallel Transport in Low-Dimensional CdTe/CdMgTe Heterostructures

We have shown that in CdTe/Cd 1-x Mg x Te heterostructures revealing parallel transport, hydrostatic pressure induces a decrease in both 2D conduction in the quantum well and in low mobility parallel channel. This behaviour, contrary to III-V heterostructures, is due to persistent decrease of the mobility. For samples having thick buffer layer the contribution of the parallel conduction is practically eliminated at high pressure with 2D conduction remaining dominant, while for samples with thin buffer layer the situation with pure 2D conduction is not achieved.