Tellurium Films Research Articles

Crystal orientation on the electrical properties of aTe-nSi heterostructure devices

The effects of crystal orientation on the electrical properties of heterostructure devices fabricated by vacuum evaporation of tellurium film (aTe) on n-type crystalline silicon wafers (nSt) with surface orientations of (100) and (111) are investigated. Two of the devices are annealed in a vacuum at a temperature of 420K for 0.5 hour. Barrier height measurement are made using the Norde's plot function. This method is less sensitive to recombination current and series resistance effects. Barrier heights of devices fabricated on nSi (100) are higher than devices fabricated on nS1 (111). Current densities in aTe-Nsi (111) devices are higher than that of aTe-nSi (100) devices. Electrical conduction in annealed devices is lower than that of unannealed devices. Nigerian Journal of Physics Vol. 16(2) 2004: 131-134

Structural and optical properties of tellurium films obtained by chemical vapor deposition(CVD)

Tellurium thin films were prepared by the chemical vapor deposition method. The structure, surface morphology and optical properties of the Te thin films were analyzed by powder X-ray diffraction, scanning electron microscopy, FTIR transmission, UV/VIS/NIR transmission and reflectance. The results show that the films structural and optical properties are influenced by many factors such as film thickness, crystallite size and substrate temperature. The films as thick as 111–133 nm have high IR transmission across the full 8–13 μm band and highly blocking in the solar spectral region elsewhere, which indicates that Te films thickness in this region can be used as good solar radiation shields in radiative cooling devices.

Growth of ultrathin films of cadmium telluride and tellurium as studied by electrochemical atomic force microscopy

Time dependent, cathodic electrodeposition of ultrathin CdTe and Te films has been studied in 50 mM H 2SO 4 + 1 mM CdSO 4 + 0.1 mM TeO 2 solutions at room temperature under potential control using electrochemical atomic force microscopy (EC-AFM). The films were also characterized electrochemically and with X-ray diffraction. The growth mechanism and the composition of the films depends on the applied potentials. Island-like growth mode was observed for CdTe films when the deposition potential was − 0.35 V (SHE). At a more positive deposition potential of 0.138 V (SHE), Cd was not codeposited into the film but affected the dynamic growth mode of the deposit. At this voltage smooth Te films were obtained. Depending on the applied potential, Cd acts either as a codeposition element for CdTe film growth, or as a mediator for layer-by-layer growth of Te films.

Studies on a-Se/n-Si and a-Te/n-Si heterojunctions

Heterojunctions are fabricated by depositing amorphous selenium (a-Se) and amorphous tellurium (a-Te) films on n-type single (n-Si) wafers by the method of vacuum evaporation. The silicon wafers have surface orientation of (111). Resistivity of each silicon wafer is 5Ω-cm and carrier concentration of 8.30 x 10 14 cm -3 . Two of the junction devices are annealed in a vacuum for half an hour. Current-voltage measurements are made at room temperature (298K). Rectification properties are observed in all the junctions. Barrier heights of a-Se/n-Si junctions are higher than a-Te/n-Si junctions. The current density in annealed junctions is lower than in as-deposited (unannealed) counterpart. @JASEM Heterojunction devices of the metal-semiconductor, semiconductor-semiconductor and amorphous semiconductor-crystalline semiconductor types have gained considerable interest from researchers both from a fundamental physics and technological viewpoint. For example, Chandra and Prasad, 1983 found that metal-semiconductor contacts (or Schottky barriers) can be used as low temperature sensors. Cross, 1992; Xiao and Whitefield, 1992 have indicated that solar cells based on silicon (Si) and Gallium Arsenide (GaAs) semiconductors can provide power for satellites and water pumping systems. Study of Mimura and Hatanaka (1987) showed that hydrogenated amorphous silicon- crystalline silicon hererojunction has application to imaging devices. Kentaro and Nakazawa, 1988; Lovejoy, 1992 have also stated that amorphous and polycrystalline thin film semiconductors have possible application in optoelectronics. Heterojuncton devices have also been studied from the viewpoint of understanding fundamental device physics. Such studies include band structure, current transport mechanism and as tools in the analysis of other physical parameters. For example, Sinha and Misra, 1983 studied the current-voltage characteristics of the junction between amorphous germanium and monocrystal p-Si at different temperatures. The authors found that the junction exhibits almost ideal Schottky diode behaviour in a narrow region of applied bias. However, the junction current at large external bias (V>300mV) is dominated by tunneling. Amorphous Selenium (aSe) and amorphous tellurium (aTe) may be obtained by thermal evaporation of materials in a vacuum. According to Kazmerski, 1980 amorphous thin films posses a large density of dangling bonds, which defy doping attempts because dopants attach themselves to these bonds. The purpose of this study is to measure the electrical properties of thermally evaporated amorphous selenium and tellurium films on n-type crystalline silicon substrates and assess the junctions for possible device application.

Room temperature operating ammonia sensor based on tellurium thin films

Tellurium thin films were studied for its use as ammonia gas sensors operable at room temperature. The films showed a reversible increase in resistance when exposed to ammonia and the response was found to be linear in the range of 0–100 ppm. The interaction of ammonia with tellurium film was investigated using Raman, XPS and impedance spectroscopy techniques. The results showed that ammonia reduces tellurium oxide on the surface and grain boundary region of the film to tellurium. This reduces majority carrier density in the film and thereby decreases the conductivity of the film.

The evolution of surface structures in p-CdTe crystals under pulsed laser irradiation

The dynamics of modification of the surface structure in p-CdTe (111) crystals subjected to nanosecond ruby laser pulses with a lasing wavelength within the fundamental-absorption region (ℏω=1.78 eV) is studied. It is shown that, depending on the radiation dose, the surface morphology changes in the following order: the formation of tellurium film, an increase in the density of dislocations under the tellurium film, and the formation of ordered quasi-periodic structures of both micrometer and nanometer size. The size of the structures and the character of their distribution are shown to be dose-dependent.

Nano-structured crystalline Te films by laser gas-phase pyrolysis of dimethyl tellurium

Pulsed CO 2 laser-induced and SF 6-photosensitized pyrolysis of dimethyl tellurium yields ethane, methane, ethene and propane, and affords chemical vapour deposition of nano-structured crystalline tellurium films. Distribution of the gaseous products (predominance of ethane) being different from that in earlier reported conventional hot-wall pyrolysis (preponderance of methane) is related to the elimination of heterogeneous steps and to the homolysis of both CTe bonds of dimethyl tellurium. The deposited tellurium films are shown as more stable against oxidation than nano-structured amorphous tellurium films deposited previously through UV laser photolysis of dimethyl tellurium.

Electrochemical Preparation of Zinc Telluride Films on Gold Electrodes

Zinc telluride films were prepared electrochemically on gold electrodes via a two-step method. The tellurium(0) was first deposited on the gold electrode by potentiostatically reducing tellurium(IV) dissolved in an acidic solution. The zinc telluride film was then prepared by potentiostatic or potentiodynamic reduction of the tellurium film thus deposited in the presence of zinc sulfate. The film deposition was supported by the frequency decreases recorded during the deposition of tellurium and zinc telluride using an electrochemical quartz crystal microbalance, as well as the spectral changes, accompanying the deposition of these films. The zinc telluride film thus prepared showed a p-type behavior as evidenced by cathodic photocurrents produced upon illumination. The bandgap energy of zinc telluride thus prepared was determined to be about 2.27 eV from its absorption spectrum. © 2003 The Electrochemical Society. All rights reserved.

Polymer-stabilized nano-sized tellurium films by laser-induced chemical vapour co-deposition process

UV laser-irradiation of a gaseous mixture of dimethyl tellurium and 1,3-disilacyclobutane induces concurrent photolysis of both compounds. Chemical changes taking place are due to expulsion of elemental tellurium from dimethyl tellurium and formation of short-lived and fast polymerizing silene from 1,3-disilacyclobutane. The co-photolysis process results in chemical vapour co-deposition of a nano-sized tellurium–polycarbosilane composite that contains amorphous nano-structures of tellurium stabilized against oxidation by organosilicon polymer.

Electrochemical synthesis of nanostructured tellurium films

Direct templating of materials via lyotropic liquid crystalline mesophases of non-ionic surfactants provides an elegant and highly versatile route to the production of a wide range of nanostructured materials with well-defined mesoporous architectures of extended spatial periodicities. This technique has now been applied in the electrochemical synthesis of adherent nanostructured tellurium films. This represents an important step towards the synthesis of II–IV semiconductor compounds such as cadmium telluride. Low angle X-ray scattering and transmission electron microscopy (TEM) studies of the resulting tellurium films indicate the presence of a system of uniform cylindrical pores organized in an hexagonal array.

Atmospheric pressure chemical vapour deposition of selenium and tellurium films by UV laser photolysis of diethyl selenium and diethyl tellurium

AbstractExcimer laser‐induced photolysis of gaseous diethyl selenium and diethyl tellurium (C2H5)2M (M = Se, Te) is controlled by cleavage of both MC bonds, it yields C1–C4 hydrocarbons (ethene as major product) and results in chemical vapour deposition of selenium films and nanosized tellurium powder. The selenium and tellurium properties were characterized by X‐ray photoelectron spectroscopy and Scanning electron Microscopy techniques. Copyright © 2001 John Wiley & Sons, Ltd.

ChemInform Abstract: Chemical Vapor Deposition of Selenium and Tellurium Films by UV Laser Photolysis of Selenophene and Tellurophene.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

High sensitive tellurium based NO 2 gas sensor

For the first time it is shown, that tellurium based thin films exhibit high sensitivity to nitrogen dioxide at room temperature. The resistance of the tellurium films decreases reversibly in the presence of NO 2. The sensitivity of this device depends on the gas concentration and it increases to lower concentrations less than 3 ppm. The response time is considerably short and in the range of 2–3 min.

Deposition of tellurium films by decomposition of electrochemically-generated H 2Te: application to radiative cooling devices

The preparation of homogenous, large area thin layers of tellurium on thin polyethylene foils is described. The tellurium was formed by room temperature decomposition of electrochemically generated H 2Te. Pre-treatment of the polyethylene substrates with KMnO 4 to give a Mn-oxide layer was found to improve the Te adhesion and homogeneity. Optical characterization of the layers was performed using UV/VIS/NIR spectroscopy. Such coatings have favorable characteristics for use as solar radiation shields in radiative cooling devices. The simplicity of generation of the very unstable H 2Te was also exploited to demonstrate formation of size-quantized CdTe nanocrystals.

Electron microscopic study of the epitaxial growth of thin single crystalline tellurium films on NaCl (001)

High resolution transmission electron microscopy, conventional transmission electron microscopy and selected area electron diffraction were applied to single crystalline thin tellurium films, which were vacuum deposited on cleaved NaCl surfaces. For the first time tellurium could be deposited as single crystalline films on rocksalt. The thin films grew with the plane (100) or (110) parallel to the substrate. The thickness of the films was 200–800 Å.

Chemical vapour deposition of selenium and tellurium films by UV laser photolysis of selenophene and tellurophene

Excimer laser-induced photolysis of gaseous selenophene and tellurophene affords gaseous 1-buten-3-yne and ethyne (as major products) and butadiyne (a very minor product) and results in chemical vapour deposition of selenium and tellurium films. The film properties were characterized by XPS and SEM techniques and by UV spectroscopy. Copyright © 2000 John Wiley & Sons, Ltd.

Natural electron oscillations in Te granules deposited on rough surfaces

Granular tellurium films deposited on rough surfaces of NaCl and KCl single crystals heated to 150 °C consist of two layers in each of which a resonance band is excited simultaneously. A band with frequency ω0 of natural electron oscillations is excited in isolated granules of the upper layer. The plasma frequency of bulk tellurium is calculated from the measured values of ω0 and the known permittivities of NaCl and KCl.

Growth and morphology of Te films on Mo

Tellurium films were deposited by thermal evaporation on a molybdenum substrate held at 120°C. The growth of the films was monitored by quantitative X-ray photoelectron spectroscopy and by atomic force microscopy. Reaction of the Te films with K vapour was also used to evaluate the thickness of the films. It has been found that for low exposures Te grows as a uniform layer, up to a thickness of about 0.4 nm. For higher exposures we observed the formation of islands of increasing thickness that cover an increasing fraction of the substrate, the remaining fraction being covered by a continuous thin layer. Implications of such a morphology on the performances of Te-based photocathodes in photo-injectors technology are discussed.

XPS, LEED and AFM investigation of the Si(100) surface after the deposition and annealing of tellurium thin films

In this study the structural properties and the morphology of the Te Si(100) 2 × 1 system after an annealing process have been investigated. Several Te Si(100) samples have been annealed at different temperatures. Up to about 150°C no changes are observed in the samples. At about 200°C the tellurium films evaporate from the silicon substrate leaving one monolayer of Te on the Si(100) surface indicating a higher strength in the TeSi bonds with respect to the TeTe one. The remaining monolayer of Te on Si(100) induces a 1 × 1 reconstruction of the surface. The annealing procedure performed at higher temperatures (more than about 400–500°C), leads to the complete removal of the tellurium. The resulting silicon surface is 2 × 1 reconstructed with a different morphology with respect to the one observed before the Te film deposition. Repeating several times the deposition of Te and the annealing procedure, at temperatures higher than about 400°C, a picturesque morphology of the silicon surface is observed.

DC conduction through UHV deposited tellurium films

The conduction characteristics of thin films of tellurium deposited between gold electrodes on an ultasonically cleaned non-alkaline Corning 7059 glass substrate in a relative oxygen-free 10 −9 mbar vacuum at 125 K have been investigated. The results show that for applied electric field of 10 8 Vm −1, the films exhibit stable but low ohmic conductance 0.25 mS of but for higher field the characteristics display non-linearity and hysteresis.