Thin Te Research Articles

TiO2/Se heterojunction photovoltaic device made from Se/Te/Se stacked precursor

This paper presents an innovative approach for forming crystallized selenium (c-Se) using a Se/Te/Se stacked precursor. The aim is to enhance the adhesion between the TiO2 and Se layers to improve the power conversion efficiency of TiO2/Se heterojunction photovoltaic devices. Our previous study revealed that the accumulation of Te near the TiO2/Se interface resulted in insufficient shunt resistance, leading to increased dark leakage current. This issue arises because Te possesses a high carrier density (∼1018 cm−3) and narrow bandgap energy (0.26 eV). However, a Te additive layer remains necessary to passivate the unbonded TiO2/Se interface and to maximize the adhesion between the absorber and the substrate. Previous research on Se-based photovoltaic devices demonstrated that an extremely thin (∼0.5 nm) and homogeneous Te adhesion layer could be formed beneath the Se photo-absorbing layer and subsequently crystallized through air-annealing post-deposition. However, achieving precise and homogeneous sub-nanometer Te films using a compact resistance heating evaporation system in a laboratory setting proved challenging so far. To address these limitations, we propose a novel technique for forming the Se absorber layer by post-annealing a stacked 1st-Se/Te/2nd-Se precursor on a TiO2 window layer. Through experimentation, we achieved the highest power conversion efficiency of 4.49 % without antireflective coating, accompanied by Voc 0.795V, JSC 11.13 mA/cm2, and FF 0.507 when the 1st-Se thickness was 5 nm. Furthermore, the impact of decreasing Te/(Te + Se) near the TiO2 window layer on photovoltaic performance was theoretically predicted using modelling by SCAPS-1D. Overall, this work introduces a promising method for enhancing the formation of c-Se, improving adhesion between TiO2 and Se layers, and enhancing the power conversion efficiency of TiO2/Se heterojunction photovoltaic devices.

Phase-engineered synthesis of atomically thin te single crystals with high on-state currents

Multiple structural phases of tellurium (Te) have opened up various opportunities for the development of two-dimensional (2D) electronics and optoelectronics. However, the phase-engineered synthesis of 2D Te at the atomic level remains a substantial challenge. Herein, we design an atomic cluster density and interface-guided multiple control strategy for phase- and thickness-controlled synthesis of α-Te nanosheets and β-Te nanoribbons (from monolayer to tens of μm) on WS2 substrates. As the thickness decreases, the α-Te nanosheets exhibit a transition from metallic to n-type semiconducting properties. On the other hand, the β-Te nanoribbons remain p-type semiconductors with an ON-state current density (ION) up to ~ 1527 μA μm−1 and a mobility as high as ~ 690.7 cm2 V−1 s−1 at room temperature. Both Te phases exhibit good air stability after several months. Furthermore, short-channel (down to 46 nm) β-Te nanoribbon transistors exhibit remarkable electrical properties (ION = ~ 1270 μA μm−1 and ON-state resistance down to 0.63 kΩ μm) at Vds = 1 V.

Environmentally Stable and Reconfigurable Ultralow-Power Two-Dimensional Tellurene Synaptic Transistor for Neuromorphic Edge Computing.

While neuromorphic computing can define a new era for next-generation computing architecture, the introduction of an efficient synaptic transistor for neuromorphic edge computing still remains a challenge. Here, we envision an atomically thin 2D Te synaptic device capable of achieving a desirable neuromorphic edge computing design. The hydrothermally grown 2D Te nanosheet synaptic transistor apparently mimicked the biological synaptic nature, exhibiting 100 effective multilevel states, a low power consumption of ∼110 fJ, excellent linearity, and short-/long-term plasticity. Furthermore, the 2D Te synaptic device achieved reconfigurable MNIST recognition accuracy characteristics of 88.2%, even after harmful detergent environment infection. We believe that this work serves as a guide for developing futuristic neuromorphic edge computing.

Tellurium Nanosphere/Hematite Hybrid Thin Films with Enhanced Light Absorption for Efficient Photocatalysis

As a semimetal, tellurium (Te) shows metallic and dielectric properties in the UV and visible ranges, respectively, and has potential as a broad-band light absorber. In this paper, plasmonic–semiconductor hybrid nanoscale films consisting of Fe2O3 thin films and Te nanospheres are designed and demonstrated. Te clusters are proved to have an enhancement of the electric near-field in a broad UV–vis–NIR spectrum, which facilitates light absorption and charge separation in photoelectrocatalysis. The thickness of Fe2O3 films is adjusted from 22 to 137 nm. The photocurrent density enhancement factor of Te-modified films is 13 times higher than that of 22 nm Fe2O3 films. Particularly, a Te-decorated Fe2O3 ultrathin film exhibits photoelectrochemical activity comparable to that of bulk Fe2O3, suggesting significant near-field enhancement from plasmon modes of the Te clusters. It is found that the Te cluster decoration led to a significant decrease of the charge transfer resistance, demonstrating that the Te clusters could boost the formation rate and suppress the recombination rate of electron–hole pairs. The hybridization of Te nanoparticles with nanoscale semiconductor films represents an efficient way to enhance the solar energy conversion efficiency.

Two‐Dimensional Tellurene Transistors with Low Contact Resistance and Self‐Aligned Catalytic Thinning Process

AbstractTwo‐dimensional (2D) tellurene (Te) has shown its great potential in nanoelectronics for its high carrier mobility and air stability. However, the high‐resistance electrical contact and relatively thick Te channel hinder its ultimate scaling and device performance. Here, the transport property of Te field‐effect transistors using platinum (Pt) contact with high work function is studied, which facilitates the effective hole injection in the p‐type Te channel. The electrical contact to Te using the Y‐function method (YFM) and the transmission line method (TLM) is investigated. The Te transistors with Pt contact show a low contact resistance of 400 Ωµm, a short transfer length of 80 nm, and low specific contact resistivity of 3.2 × 10−7 Ωcm2, resulting from the low Schottky barrier height (SBH) of Pt/Te interface. The Pt electrode also can work as an efficient catalyst that allows reduction of the Te channel thickness with a controllable thinning process in water under white light illumination. This self‐aligned catalytic thinning process enables the construction of the transistors with a thin Te channel and thick Te contact with Pt metal electrodes, which provides a device configuration with both effective electrostatic control and low contact resistance.

Tellurium-based chemical sensors

Abstract The various tellurium-based chemical sensors are described. This article focuses on four types of Tellurium sensors such as CdTe quantum dots-based sensor, Te thin films-based sensor, Te nanostructures or nanoparticles-based sensor, and TeO2-based sensor.

High-quality two-dimensional tellurium flakes grown by high-temperature vapor deposition

Large-area and high-quality 2D Te flakes were synthesized by high-temperature vapor deposition using In2Te3 powder as source. The thin Te flakes exhibit low electrical resistivity, high hole mobility and ultrahigh photoresponsivity in visible range.

One-Pot Hydrothermal Synthesis of Thin Tellurene Nanosheet and Its Formation Mechanism

Two-dimensional thin tellurene (Te) was effectively synthesized by a one-pot hydrothermal reduction process. It had the hexagonal phase with good crystallization, the extent of radiation absorption (400-850 nm), and a 1.37 eV band gap. Based on the evolution of the crystal structure and morphology, the formation mechanism of Te nanomaterials has been speculated by the time-dependent reactions as the nucleation of nanosized clusters first, then self-assembly into uniform nanowires, and, finally, formation into the nanosheets in the presence of polyvinylpyrrolidone (PVP). It is expected that thin Te nanosheets can further be used in the field of photoelectric applications.

Room temperature growth of silver telluride nanorods by sputtering deposition

We report on the growth of silver telluride nanorods by radio frequency (RF)-magnetron sputtering at room temperature. We find that a sputtering deposition of Te onto Ag nanoparticles spontaneously forms nanorods with a typical diameter of 15 nm and a length of 200 nm. Each nanorod has an amorphous core with a composition close to Ag2Te, covered by a thin Te shell layer. We propose a growth mechanism, based on a strong Ag-Te reaction and solid-state amorphization.

Long-range p–d exchange interaction in a ferromagnet–semiconductor hybrid structure

Hybrid structures synthesized from different materials have attracted considerable attention because they may allow not only combination of the functionalities of the individual constituents but also mutual control of their properties. To obtain such a control an interaction between the components needs to be established. For coupling the magnetic properties, an exchange interaction has to be implemented which typically depends on wave function overlap and is therefore short-ranged, so that it may be compromised across the interface. Here we study a hybrid structure consisting of a ferromagnetic Co-layer and a semiconducting CdTe quantum well, separated by a thin (Cd,Mg)Te barrier. In contrast to the expected p-d exchange that decreases exponentially with the wave function overlap of quantum well holes and magnetic Co atoms, we find a long-ranged, robust coupling that does not vary with barrier width up to more than 10 nm. We suggest that the resulting spin polarization of the holes is induced by an effective p-d exchange that is mediated by elliptically polarized phonons.

Fabrication of flexible thermoelectric thin film devices by inkjet printing.

Ink-jet printing of thermoelectric nanomaterials is successfully used to fabricate flexible thin film TE devices for power generation and cooling.

Growth and alloying of thin film Te on Cu(111)

We explore the growth and temperature-dependent alloying of Te on Cu(111) using a combination of low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and scanning tunnelling microscopy (STM). Below 275K, growth is rough and disordered. Above 275K, there are two distinct surface phases: a surface substitutional alloy for coverages below 0.33ML and a Cu3Te2-like alloy above 0.66ML, with the phases coexisting at intermediate coverages. The alloy is consistent with the (111)-termination of an unusual phase with F4¯3m-symmetry that is well lattice-matched to the underlying Cu(111). It is relaxed and incommensurate, showing a long-range periodicity consistent with a floating overlayer.

Optical and gas sensing properties of thick TiO 2 films grown by laser deposition

In this work the optical and the gas sensing properties of thick TiO 2 waveguide films, produced by pulsed laser deposition, were investigated by m-line spectroscopy. The films were deposited on (0 0 1) SiO 2 substrates at temperature of 100 °C. The thickness of the films was measured to be in the range from 650 to 1900 nm and the roughness increases from 5 to 14.6 nm. High quality mode spectra, consisted of thin and bright TE and TM modes, were observed in the films with thickness up to 1200 nm. All the films revealed anisotropic optical properties. Gas sensitivity of the films to CO 2 was examined at room temperature on the basis of the variations of the refractive index. CO 2 concentration of 3 × 10 4 ppm was detected, which corresponds to a refractive index variation of about 1 × 10 −4. The crystal structure and the optical transmittance of the films were also presented and discussed.

Characterization of tellurium layers for back contact formation on close to technology treated CdTe surfaces

We have studied the contact formation on CdTe surfaces following the technologically applied procedure. The electronic properties of wet chemically etched CdTe surfaces has been investigated with photoelectron spectroscopy. For the characterization of the morphology, structure, and elemental distribution in the etched layer atomic force microscopy, scanning electron microscopy, grazing incidence x-ray diffraction, and secondary ion mass spectroscopy have been used. Etching of the samples has been performed in air and in an electrochemistry chamber directly attached to the UHV system. In both cases the formation of an elemental polycrystalline Te layer with a thickness of about 80 Å is detected. For comparison, a thin Te layer has been deposited by physical vapor deposition onto a CdTe substrate. We determine a valence-band offset of ΔEVB=0.5±0.1 eV, independent of the preparation of the interface.

Structural, Optical and Thermal Properties of Bulk Zn1?xBexTe Crystals

Bulk Zn1–xBexTe crystals were grown in the range extending up to x = 0.12. Their structural, optical and photothermal properties were characterised using X-ray diffraction, photoluminescence (PL) and photoacoustic (PA) methods. The lattice constants are found to follow a linear dependence on x. Energy gap and thermal diffusivity were determined from photoacoustic spectra. The energy-gap increasing trend with rising beryllium content is in agreement with that reported for thin (Zn,Be)Te layers on InP substrate.

Electrodeposition and characterization of CdTe thin films on Mo foils using a two voltage technique

Polycrystalline thin film CdTe-based solar cells are one of the most promising candidates for low-cost terrestrial conversion of solar energy because of the optimum energy band gap ( E g =1.44 eV ) and high absorption coefficient of CdTe. In this work, a two-step electrodeposition technique has been used to prepare CdTe thin films from acidic solutions. In the first step, a thin Te rich CdTe layer was deposited at –300 mV (SCE) on a Mo foil substrate. On top of this film, a Cd rich CdTe layer was deposited at more negative voltages. The resulting films showed good adherence to the substrate and very low contact resistance between the substrate and the p+ Te rich CdTe layer. The composite film was of nearly stoichiometric composition. From X-ray diffraction results, the as-deposited films show very small grain sizes but after annealing the grain size increases considerably showing very well-defined peaks. The morphological, structural and composition results of CdTe thin films obtained by Scanning Electron microscopy, X-ray diffraction, and X-ray fluorescence will be presented. Electrical properties such as conductivity type and contact resistance values for the Mo/CdTe structures will also be presented.

Growth and physicochemical characterization of CuAlTe2 films obtained by reaction, induced by annealing, between Cu/Al/Te/Al/Cu... Al/Cu/Al/Te layers sequentially deposited

CuAlTe2 thin films have been synthesized by annealing under an argon flow a multilayer structure of thin Cu, Al and Te layers sequentially deposited by evaporation under vacuum. The films have been characterized by X-ray diffraction, microprobe analysis, photoelectron spectroscopy and Raman scattering. At the end of the process, the XRD spectra demonstrate that textured CuAlTe2 films have been obtained with preferential orientation of the crystallites along the (112) direction. The Raman patterns are in good accordance with the reference. The XPS spectra show that the binding energies of the elements are in good agreement with bonds of CuAlTe2. Even after a decrease of the oxygen contamination by improvement of the depositing process the oxygen present in the films is found to be about 12 at %.

Atomic structures and growth mechanisms of electrodeposited Ag and Te films as discerned by atomic force microscopy

We have investigated atomic structures as well as growth morphologies of electrodeposited thin Ag and Te films on Au(100) under an aqueous sulfuric acid solution. The extremely flat Ag films were formed by an ideal Frank–van der Merwe mode even at a high deposition rate [∼7.2 monolayer (ML)/min], which suggests that the surface diffusion process of Ag adatoms is extremely rapid. In the underpotentially deposited Te on Au(100), the (√2×√2)R45°-Te structure (coverage, θ=0.5) for a first monolayer was formed through the (2×2)-Te structure (θ=0.25) under an aqueous H2SO4 solution. In contrast with the Ag films, the bulk deposited Te films were formed by a Stranski–Krastanov mode even at a low deposition rate (∼0.5 ML/min), which suggests that the surface diffusion process of Te adatoms is extremely slow. The Te(101̄0) films (≳80 ML) were grown on Au(100) through the c(√2×3√2)R45° (20–30 ML) and (√2×√2)R45°-Te(<10 ML) structures.

Properties of CdTe solar cells electrochemically prepared from single crystals

Optoelectrical properties of junctions electrochemically formed on the surface of n-type CdTe single crystals are reported. The carrier transport process across the junction is controlled by tunnelling through the barrier from one side and by thermal emission followed by recombination at interface states from the opposite side of the junction. The CU characteristics have the shape typical for abrupt junctions and the built-in potential UD = 1.1 V confirms the formation of an np homojunction covered by a thin Te film. The photovoltaic parameters of these cells are: open-circuit voltage 0.42 V short-circuit current density 0.5 to 0.8 mA/cm2, and fill factor 0.54. The spectral response indicate that the thin layer of Te acts only as an optical filter.

In situ ellipsometry studies of electrodeposited cadmium telluride films on cadmium mercury telluride

The electrodeposition of CdTe on CdxHg1-xTe is carried out from aqueous solutions at 55 degrees C and the film growth is monitored using in situ ellipsometry. The measurements reveal that, at a growth potential of -0.55 V versus SCE, a thin (120 AA) Te layer is initially formed on the surface followed by the growth of the CdTe film (1.8 mu m) which appears to be of uniform composition for most of its thickness. Further analysis of the film using the techniques of Raman spectroscopy, differential scanning calorimetry (DSC) and energy dispersive X-ray analysis (EDAX) confirm the excess tellurium in the electrodeposited film. The EDAX measurements after electrodeposition also reveal the presence of 2-8% Hg in the film depending on the depth of analysis. The presence of Hg in the film can only be explained by the diffusion of Hg from the substrate through the electrodeposited layer.