P. Sutta

Structural properties of amorphous silicon prepared from hydrogen-diluted silane

A systematic structural analysis was carried out on amorphous silicon films prepared from hydrogen-diluted silane using plasma-enhanced chemical vapor deposition. Hydrogen dilution of silane during the growth of a-Si:H absorber layers is used to suppress light-induced degradation of a-Si:H solar cells. Transmission electron microscopy (TEM) shows that for higher hydrogen dilution ratios the growth of films becomes strongly inhomogeneous and the transition from amorphous to microcrystalline phase occurs at a smaller thickness. A detailed X-ray diffraction (XRD) analysis of the amorphous films reveals that the strongest peak in the XRD patterns is located around 27.5° and corresponds to the signal from the ordered domains of tetragonal silicon hydride and not from cubic silicon crystallites. The full width at half maximum of this peak narrows from 5.1° to 4.8° as the ratio of hydrogen to silane flow (R) increases to 20 and does not change significantly for higher hydrogen dilutions. The presence of silicon hydride ordered domains in amorphous films is confirmed by the lattice imaging method applied to the high resolution TEM recordings. The amorphous silicon films fabricated at different hydrogen dilution were applied as absorber layers in single-junction solar cells. The degradation experiment confirms that the cells with absorber layers deposited using hydrogen dilution are more stable to light exposure. A clear reduction of the degradation is observed when the dilution ratio is increased from R = 0 to R = 20. The degradation of solar cells with absorber layers prepared at R > 20 is not reduced by further increasing R.

Phase Control and Stability of Thin Silicon Films Deposited from Silane Diluted with Hydrogen

Hydrogen dilution of silane during the rf-PECVD growth of a-Si:H absorber layers is used to suppress light-induced degradation of a-Si:H solar cells. The increased stability of cells and films deposited using hydrogen dilution is verified in an accelerated degradation experiment. At higher hydrogen dilutions the early phase transition to the microcrystalline phase complicates the growth of fully amorphous films as absorbers with a sufficient thickness. In a systematic study on the influence of various deposition conditions on the material properties the pressure is identified as an important factor for controlling the structural phase evolution of the films.

Piezoelectric ZnO thin films prepared by cyclic sputtering and etching technology

A novel procedure of ion assisted deposition technology consisting of cyclic sputtering and ion etching is presented. Cross-resistivities of ZnO films deposited by that technique increased up to 10/sup 10/ /spl Omega/cm due to the formation of buffer regions in the films. These ZnO films with the piezoelectric coefficient of the order of 10/sup -12/ m/V are applicable in low-frequency microactuators.

Preparation of shell nanocrystalline Ga-doped ZnO ultra-thin films by sputtering

In this paper the possibility to form ultra-thin homogenous films doped by Ga (ZnO:Ga) by continual or sequential sputtering is presented. An influence of post-deposition annealing on crystalline structure of films was studied. The ability to create a highly consistent coverage (shell) of three dimensional nanostructures (GaP nanowires) by the sequential mode of sputtering was proven.

P-Type Conduction in Sputtered ZnO Thin Films Doped by Nitrogen

Nitrogen doped zinc oxide (ZnO:N) thin films were prepared by RF diode sputtering from ZnO target in different ratio of Ar/N₂ gas mixture. The p-type features of ZnO:N thin films have been caused by the incorporation of the nitrogen acceptor NO into ZnO what was proven by second ion mass spectroscopy (SIMS) analysis. The minimum value of resistivity of 790 Omegacm, a Hall mobility of 22 cm²V^-1s^-1 and the carrier concentration of 3.6 times 10¹⁴ cm^-3 were yielded at 75 % N ₂. X-ray diffraction measurements (XRD) showed that ZnO:N films had the preferential orientation of (002) plane at 25 % N₂ and of (100) plane for higher N₂ concentrations. The average grain size was from 7 to 42 nm for all Ar/N₂ ratios. ZnO:N films exhibit relatively high micro strains (10 times 10^-3)

Structural and mechanical behaviour of LLDPE/HNT nanocomposite films

The paper briefly describes structural and mechanical influences of Halloysite nanotubes (HNT) in different level of fulfilment (0, 1, 3, 7 wt%) in the LLDPE commonly used in the cable industry. The influence of HNT on the polymer has been observed and evaluated through the average crystallite size and the micro- deformation by X-Ray diffractometry and the imaging of SEM. Despite the certain inter-phase tension between the polymer and HNT, the influence on the mechanical and combustion behaviour was observed. Measurement showed a higher content of agglomerates in the sample with 7 wt% HNT fulfilment.

Optical properties of zinc titanate perovskite prepared by reactive RF sputtering

Abstract In this paper we report results from optical transmittance spectroscopy complemented with data on structure from XRD measurements to determine optical properties of a series of ZnTiO3 perovskite thin films deposited on glass by reactive magnetron co-sputtering. The members of the series differ by the titanium content that was revealed as an origin of the changes not only in structure but also in dispersive optical properties. Low porosity has been discovered and calculated using the Bruggeman effective medium approximation. An apparent blue-shift of the optical band gap energies with increasing titanium content was observed. The observed band gap engineering is a good prospective for eg optoelectronic and photocatalytic applications of ZnTiO3.

Sputtering of ZnO:Ga thin films with the inclined crystalic texture

In this paper the possibility to form thin films with the inclined crystalic texture by the RF diode sputtering is presented. Two oblique deposition arrangements were used for the preparation of ZnO:Ga thin films with the deviation of their columnar structures in the range of 12 ÷ 15 deg to the substrate normal, i.e. an inclination of their ordinary optical axis. The inclined texture of films has changed their optical transmittance spectra as well as it caused the blue-shift and the change of the optical band-gap.

Structure and optical properties of the hydrogen diluted a-Si:H thin films prepared by PECVD with different deposition temperatures

The paper deals with the hydrogenated amorphous silicon (a-Si:H) films about 300 nm in thickness prepared by using rf-PECVD with hydrogen dilution R = 10 of the silane source gas in the amorphous growth regime onto clean Corning Eagle 2000 glass substrates at different deposition temperatures ranging from 50 to 200 °C. Structural and optical properties of the films were obtained from X-ray diffraction and UV-Vis spectrophotometry. The full width at half maximum of the first scattering peak decreases with increasing of the deposition temperature up to 150 °C and then remains constant. Optical band-gaps are from 1.65 to 1.76 eV, which slightly decrease with increasing deposition temperature, whereas the refractive index increases with increasing deposition temperature. This indicates that the density of the films at higher temperature has increased.

ZnO Doping and Co-doping Paradigm and Properties

Here, we report on experimental studies of the role of doping and co-doping on the properties of ZnO thin films deposited by radio-frequency diode sputtering at varying nitrogen content (0 ÷ 100%) in the sputtering Ar/N 2 gas. Co-doping improved the crystalline structure, and ZnO:Al:N films maintain a c-axis texture in the direction of the surface normal. Depending on the N 2 content, the estimated crystallite size varies from 8 to 37 nm for ZnO:N and 21-33 nm for ZnO:Al:N. Nitrogen doping results in an increased absorption around the bandedge and the bandgap narrowing (E g < 3.2 eV).