Narrow Results

In order to improve the photoelectric transformation efficiency of thin-film solar cells, one plausible method was to improve the transparent conductive oxides (TCO) material property. In-doped tin oxide (ITO) was an important TCO material which was used as a front contact layer in thin-film solar cell. Using magnetron sputtering deposition technique, we prepared preferential orientation ITO thin films on quartz substrate. XRD and SEM measurements were used to characterize the crystalline structure and morphology of ITO thin films. The key step was adding a ZnO thin film buffer layer before ITO deposition. ZnO thin film buffer layer increases the nucleation center numbers and results in the (222) preferential orientation growth of ITO thin films.

This work explores the structural, surface and optical properties of NiO films grown on Si, GaAs, PET and glass substrates. The NiO films were deposited on these substrates under same conditions by using radiofrequency (RF) magnetron sputtering of NiO target at 100${}^{\circ }$C. The structural study by X-ray diffraction (XRD) showed the existence of (200) and (220) oriented NiO peaks on all the substrates. The preferred orientation of NiO films on Si, GaAs and glass was along (200) plane whereas the film grown on PET was observed to be oriented along (220) plane. The crystallite size of NiO on GaAs was the largest among the other substrates. The RMS surface roughness on PET was higher as compared to the other substrates. The band gap of NiO films grown on glass and PET was estimated from UV–Vis transmittance spectroscopy whereas the UV–Vis reflection spectroscopy was carried out to find out the band gap of NiO grown on GaAs and Si substrates. The band gap of NiO on PET was higher than its band gap obtained on other substrates. The results obtained on properties of NiO films on different substrates were correlated with each other.

Nano-crystalline copper oxide films were deposited on quartz substrates by RF-magnetron sputtering in argon gas environment. The XRD patterns show Cu₄O₃ phase for films deposited at 50 and 60W of RF power. The film deposited at 70W shows existence of Cu₄O₃ and CuO phases, whereas film deposited at 100W of RF power consists of only CuO phase. Raman spectra and transmission electron microscopy (TEM) also confirm these results. Field emission scanning electron microscopy (FESEM) shows morphological changes in the film as a function of RF power. The optical band gap estimated from the transmission spectra of the films are 2.3 and 1.7eV for Cu₄O₃ and CuO phase, respectively. The hydrothermal heat treatment of the film leads to transformation of Cu₄O₃ to CuO phase in the film.

ZnO thin films were deposited on quartz substrates by RF sputtering under argon, oxygen and nitrogen gas environment. The as deposited films showed hexagonal wurtzite structure with (002) orientation along c-axis. The mechanical properties of films with thickness ranging from 842nm to 1067nm and grain size 94–124nm were studied using nanoindentation technique. The Young’s modulus and hardness of the films were in the range 76–257GPa and 5–18GPa, respectively. Both parameters decreased with increase in indentation depth of the films. The spatial distribution of these parameters were strongly dependent on the gas environment used for film deposition.

ZnO thin films were grown by the RF magnetron sputtering technique at different substrate temperatures, from RT to 300°C. The crystallite size was calculated from XRD and the grain size was measured from AFM for different substrate temperatures. The influence of the substrate temperature on the electrical properties of the films was investigated through the Hall effect, and conductivity studies were performed under UV light illumination. The conductivity and the carrier mobility of the films were found to increase with increasing substrate temperature, which can be due to the grain-boundary-dominated conduction mechanism. The thermal activation energy and photosensitivity of the films were calculated, and the results are presented in this paper.

Photoconducting properties of indium tin oxide (ITO) nanowires grown by RF sputtering associated with annealing process were studied. ITO nanowires have been grown without the use of catalysts or oblique deposition. The cubic cross-sectional nanowires length was of the order of several microns, while their diameter was ~150–250 nm. The photoluminescence (PL) analysis on nanowires proved their excellent photoemission characteristics. Devices based on ITO nanowires showed a substantial increase in conductance of up to three orders of magnitude upon exposure to UV light and showing reproducible UV photoresponse and remaining relatively stable. The rising speed is slightly reduced, while the decay time is prolonged. Such devices also exhibited short response times and significant shifts in the threshold gate voltage. It was found that the dynamic response of the ITO nanowires phototransistor was stable with an on/off current contrast ratio of around 10¹. It is thus found that the change in the carrier concentrations in constant gate voltage was enhanced by 1.12 × 10¹⁷ cm^-3 for the 350 nm UV light, corresponding to threshold-voltage shifts of before to after UV-light exposition. The photoconductive gain corresponding to responsivity measured at 350 nm was 0.11 × 10⁵.

Doped lead–zirconate–titanate (PZT) thin films are preferred for the development of micro–electro–mechanical systems (MEMS)-based acoustic sensors because of their inherent higher dielectric and piezoelectric coefficients. Patterning process is used to develop such MEMS devices which is highly complex even for undoped PZT thin films; therefore, the problem is further cumbersome for doped PZT thin films due to the presence of added dopant elements and their associated chemistry. This paper presents patterning of strontium (Sr) and lanthanum (La) co-doped PZT thin film (PSLZT) deposited on platinized silicon substrate using wet and dry etching processes for fabricating a diaphragm structure with thickness of 15–25$\mu$m and diameter of 1.4–2mm, suitable for acoustic sensing applications. The effects of various etching conditions have been studied and the results are reported. It is found that the dry etching is the most suited process for realizing the piezoelectric MEMS structure due to its higher etching resolution. An appreciable etching rate of 260–270nm/min with smooth vertical sidewalls is achieved. The silicon diaphragm with patterned PSLZT thin film is found to retain more than 80% of its dielectric and piezoelectric coefficients and has a resonance of 1.43MHz.