Cu-doped Thin Films Research Articles

Cu-doped NiO thin film's structural, optical, and electrical properties and its negative absorption behaviour in the Infra-Red region

NiO undoped and Cu-doped thin films on FTO-coated glass (fluorine-doped tin oxide) are prepared by employing the sol-gel spin coating method. The Cu-doping effect was observed in all the characterized reports such as absorption, transmittance, field emission scanning electron microscope (FESEM), Grazing Incidence X-ray Diffraction (GIXRD), photoluminescence (PL), Raman spectra, current-voltage measurement (IV), and X-ray photoelectron spectroscopy (XPS). Enhancement in electrical conductivity due to Cu doping and IR illumination has been found. Band gap can also be tuned by varying doping concentrations. One new phenomenon called negative absorption (NA) has been found while investigating the optical properties in the infrared (IR) region for both undoped and Cu-doped NiO on the FTO substrate, which opens a new door for advanced research. The multifarious properties of NiO thin films offer various applications in many different fields.

Analysis of the Effect of Copper Doping on the Optoelectronic Properties of Indium Oxide Thin Films and the Thermoelectric Properties of an In2O3/Pt Thermocouple

The detection and real-time monitoring of temperature parameters are important, and indium oxide-based thin film thermocouples can be integrated on the surface of heaters because they operate normally under harsh conditions and provide accurate online temperature monitoring. The higher stability and appropriate optical and electrical properties of In2O3 make it very suitable as an electrode material for thermocouple sensors. This work demonstrates that copper doping can alter the optical and electrical properties of In2O3 films and regulate the output performance of thermocouples. Copper-doped In2O3 thin films were prepared using the magnetron co-sputtering method. The doping concentration of Cu was controlled using direct current (DC) power. An In2O3/Pt thermocouple sensor was prepared, and the optoelectronic and thermocouple properties were adjusted by changing the copper doping content. The thickness valve of the thin film sample was 300 nm. The results of the X-ray diffraction suggested that the structure of the doped In2O3 thin films was cubic. The results of the energy-dispersive X-ray analysis revealed that Cu was doped into the In2O3 thin films. All deposited films were n-type semiconductor materials according to Hall effect testing. The 4.09 at% Cu-doped thin films possessed the highest resistivity (30.2 × 10−3 Ω·cm), a larger carrier concentration (3.72 × 1020 cm−3), and the lowest carrier mobility (0.56 cm2V−1s−1). The optical band gap decreased from 3.76 to 2.71 eV with an increase in the doping concentration, and the transmittance of the film significantly reduced. When the DC power was increased, the variation range of Seebeck coefficient for the In2O3/Pt thermocouple was 152.1–170.5 μV/°C, and the range of thermal output value was 91.4–102.4 mV.

Sol–Gel-Derived Cu-Doped ZnO Thin Films for Optoelectronic Applications

Pristine and Cu-doped ZnO thins films were deposited on Si(100) and quartz substrates by the sol–gel method, followed by post annealing at 450 °C. Structural analysis shows that all grown films are polycrystalline in nature and the crystallite size of the doped film increases with the doping concentration. Narrowing of the band gap is seen with Cu doping, and electrical analysis shows an increase in the conductivity and carrier concentration with Cu doping. As compared to pristine ZnO, Cu-doped thin films show p-type conductivity with a maximum carrier concentration of 1.34 × 1015 cm–3 for 6% doping at room temperature. The p-type conductivity in these films easily degraded with time, which may be due to the interaction of films with ambient conditions or may be due to the diffusion of indium inside the material. After 15 days, ambient-exposed films were totally converted into n-type, whereas the vacuum-placed film still shows p-type behavior with good mobility. This study shows that sol–gel-derived Cu-doped thin films show low electrical resistivity, p-type conductivity, and high transmittance and can be used for optoelectronics devices if these films were well prepared, protected, and properly passivated.

Thermal stability and crystallization speed of Cu-doped Ge8Sb2Te11 thin films

The objective of this study was to evaluate structural and electrical properties of Cu-doped Ge8Sb2Te11 thin films. Thermal stability and crystallization speed in nanosecond time scale of these of Cu-doped Ge8Sb2Te11 thin films prepared by a radio frequency (RF) magnetron reactive sputtering were also determined. A one-step phase transformation from an amorphous phase to a face-centered-cubic (fcc) phase and an increase of crystallization temperature (Tc) were observed for the Cu-doped film, indicating an enhanced thermal stability in the amorphous state. The sheet resistance (Rs) of the amorphous phase in the Cu-doped film was about 1.5 orders of magnitude larger than that in undoped film. The larger Rs, in the amorphous phase will reduce the programming current in the memory device. An increase of threshold voltage (Vth) was seen in the Cu-doped thin film, implying a high thermal efficiency. The SET voltage of the Cu-doped film was improved with an increase of the pulse voltage. The SET speed of the Cu-doped thin film was about 30 ns, suggesting that such thin film could be a good candidate for the fast crystallization PRAM.

Electrodeposition of copper-doped SnS thin films and their electric transmission properties control for thermoelectric enhancement

The thermoelectric performances of SnS are gradually noticed because of its structure similarity to SnSe which has the highest known thermoelectric performance. But the low electric transmission properties of SnS confines its thermoelectric performances. In this paper, we prepared Cu-doped SnS thin films with electrodeposition method. The Cu-doping content of the thin films were controlled by the adjustment of the electrolyte composition. The Cu doping narrowed the band gap of the SnS thin films, so that it promoted the carrier concentration of the films. The largest carrier concentration increased from 4.26 × 1015 to 436.42 × 1015 cm−3 after the Cu doping. By the additives in the electrolyte, the texture orientation and its coefficient were successfully controlled. The texture of (040) and (200) were obtained by the addition of urea and CTAB, respectively. The carrier mobility of the Cu-doped SnS thin films increased from 0.63 to 1.94 cm2/V s by the (200) texture. With a sample electrodeposition method, we successfully accomplished the combination of the Cu-doping and texture control of SnS thin films. Such a combination decreased the resistivity of the Cu-doped thin film with (200) texture from 322.53 to 24.50 Ω cm, so it was an effective path to improve the electric transmission performance of SnS thin films. Our results provide an easy method and a new view to improve the electric transmission performance of thermoelectric thin films.

HUMIDITY-DEPENDENT IMPEDANCE AND DFT ANALYSIS OF PURE AND Cu-DOPED SnO2 THIN FILMS

Tin Oxide has been explored for gas sensing and humidity sensing. In the present work, pure and copper-doped SnO2 is synthesized by controlled spray pyrolysis technique. The films are homogeneous throughout. Rietveld analysis confirms the absence of other phases due to doping. The optical property is studied using UV-Visible spectroscopy which shows a change in the band gap with the introduction of the dopant. An elaborate impedance analysis is carried which showed the effect of doping. Cu-doped thin film showed a faster drop in the impedance when exposed to humidity. Significant change in the cole–cole plot is observed indicating better sensitivity with the doped sample in comparison to undoped. Higher humidity level from 80 to 92 RH is studied as it is important to detect the same in air conditioning systems, electronic devices, aviation systems and food processing systems. The equivalent circuit also reveals that the adsorption of water molecules on the surface of the thin films changes the impedance characteristics. Levenberg–Marquardt algorithm is employed for the theoretical calculations and identifying the equivalent circuit. The charge transfer in the doped sample is subjected to lesser grain resistance according to theoretical calculation and experimental results. A density functional approach is employed to study the band structure and explain the influence of Cu doping on pure SnO2. The calculated result supports the use of Cu as a dopant for better humidity sensing device.