Characterization of CdTe with photoelectronic techniques

Thermally stimulated current (TSC) and space-charge limited current (SCLC) measurements have been performed in CdTe grown by Bridgman method with various In dopings and grown from Te-rich solution with Cl doping. Hole traps have been evidenced at 0.07, 0.14, 0.25 and 0.36 eV from valence band, while electron traps are at 0.05, 0.34, 0.52 and 0.62 eV from conduction band. Measurements of activation energies of resistivity vs temperature curves indicate which of these should correspond to donors or acceptors centers. Various methods of analysis were used both for TSC and for SCLC results, in order to determine the more suitable ones. Finally TSC and SCLC are compared and discussed as methods for CdTe characterization.Des mesures de courants thermostimulés ou limités par charge d'espace ont été employées pour caractériser des cristaux de tellurure de cadmium préparés soit par la méthode de Bridgman (avec différents niveaux de dopage à l'In) soit par le procédé THM sous solvant tellure (avec dopage au C1). Les pièges suivants ont été identifiés : pour les trous, des niveaux localisés à 0,07, 0,14, 0,25, 0,36 eV de la bande de valence, pour les électrons à 0,05, 0,34, 052 et 0,62 eV de la bande de conduction. A partir des mesures de résistivité en fonction de la température il a été possible de déterminer les niveaux donneurs et accepteurs, respectivement. L'analyse des courbes de courants thermostimulés et de charge d'espace a été effectuée de plusieurs façons, afin de déterminer les conditions optimales d'analyse. Finalement, les mérites respectifs de ces deux procédés de caractérisation seront discutés dans le cas où elles sont mises en œuvre sur CdTe

Porous tellurium oxide microtubes for room-temperature NO2 gas sensors

The sensing properties of porous TeO2 microtubes were observed from the electrical conductance change under NO2 gas at various concentrations and at room temperature. The sensors were fabricated by the thermal annealing of Te microtubes at 420 °C for 2 h in oxygen atmosphere. It was found that the sensitivity increased with NO2 concentration in the range 5–200 ppm and tended to saturate at higher concentrations. The response time decreased and the recovery time increased as gas concentration was raised, whereas at higher concentration the response and recovery times tended to constant values. The sensitivity, response and recovery times at 100 NO2 ppm were 75%, 100 s and 450 s, respectively. The sensors showed good stability and reproducible response throughout the test period

Characteristics of molybdenum trioxide nanobelts prepared by thermal evaporation technique

Single-crystalline nanobelts of molybdenum trioxides (MoO(3)) were grown by a thermal evaporation method of molybdenum metal pellets at ambient pressure in a flow of O(2). The chemical composition, crystalline structure and optical properties of the nanobelts were investigated by various characterization techniques such as scanning electron microscopy, transmission electron microscopy, Raman-scattering, energy dispersive X-ray spectroscopy and UV-vis-NIR spectroscopy. The samples were nanobelts with a width up to 50 mu m, about 85 nm in thickness and from tens to several hundred micrometers in length. The analysis indicated that as-synthesized samples were orthorhombic structured MoO(3) grown with [0 0 1] preferred orientation. The fundamental optical absorption edge corresponds to direct allowed transitions with an energy gap located at about 3.01 eV

“Thermal oxidation of amorphous GaSe thin films”

In this work the results of the thermal oxidation of GaSe thin films in air at different temperatures are presented. The structural and morphological characteristics of the thermally annealed products were studied by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The as-deposited GaSe films were amorphous and they transformed into polycrystalline GaSe films with a hexagonal crystal structure at a temperature around 400°C. Thermal oxidation at 650°C resulted in the formation of mixed Ga2Se3 and Ga2O3compounds both in the monoclinic phase. At higher temperatures, Ga2Se 3 disappeared and complete oxidation of the initial compound occurred. The optical energy gaps of products were determined at room temperature by transmittance measurements using UV-vis-NIR spectroscopy

“Room temperature NO2 sensing properties of reactively sputtered TeO2 thin films”

Tellurium oxide (TeO(2)) thin films were deposited on quartz substrates by sputtering a Te metal target in an Ar + O(2) gas mixture. The structure and phase identification of the samples were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The as-deposited films were amorphous and became crystalline after thermal annealing at 500 degrees C. The optical energy gap of the films was determined from transmittance and reflectance spectra. The direct energy gap values were found to be 3.81 eV in as-deposited films and 3.73 eV in thermally annealed samples. Properties of the TeO(2) thin films for NO(2) gas sensing at room temperature were also investigated. The as-deposited films showed negligible sensitivity to NO(2) gas. On the contrary the films prepared by thermal annealing showed a promising sensitivity and response towards tested gas