H. Nichev

Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron sputtering

Structural, optical and electrical properties of V doped ZnO thin films deposited by r.f. magnetron co-sputtering on glass substrates at different temperature, Ts, between 150°C and 500°C are studied. The EDS analyses indicate that the average vanadium content in the films is in the range of 0.86–0.89 at. %. XRD spectra demonstrate preferential (002) crystallographic orientation with c-axis perpendicular to the substrate surface and grains sizes of the films about 21–29 nm. The band gap energy, Eg, values are in the range of 3.44–3.47 eV. The deposited V doped ZnO films have low resistivity − (2–8). 10−3 Ω cm. Raman spectra show vibrational phonons modes typical for ZnO. Comparison with the structural, optical and electrical properties of thin films ZnO and ZnO:Al is given.

Sensitivity of Co doped ZnO films to NH3 at room temperature - influence of the deposition temperature

The sensitivity was studied of undoped ZnO films and doped with Co (ZnO:Co) to exposure to NH3. The films were deposited by magnetron sputtering of a sintered ZnO target and co-sputtering of the ZnO target with Co chips on its surface. The influence of the substrate temperature, Ts, on the properties of the films was studied. The structural and optical properties of the undoped and Co doped ZnO films were studied by X-ray diffraction spectroscopy (XRD) and optical transmittance and reflectance. The optical band gap of the films was calculated. The variation of the sensitivity of films deposited at different Ts with the NH3 concentration is presented. The results demonstrate that the Co doped ZnO films have a higher sensitivity to ammonia and their sensitivity increases with Ts.

Preparation of wire structured ZnO films by electrochemical deposition

This article reports the synthesis of wire structured ZnO by electrochemical deposition on a glass substrate covered by thin film of ITO or SnO2 doped with F (SnO2:F) and on a carbon tissue. The influence of the structure of the transparent conductive films on the structural properties of the ZnO films obtained was studied by SEM and Raman spectroscopy. The results show that the films have a columnar structure with grain size of about 200-500 nm. The films deposited on the SnO2:F coated glass substrate have better structural properties. Pillar structure is observed on the surface of the fiber of the carbon tissue.

Influence of the hydrogen content in a-Si:H layers on the structural properties of poly-Si films obtained by AIC of glass/Al/a-Si:H structures

Polycrystalline silicon films were fabricated by aluminium-induced crystallization of glass/Al/a-Si(a-Si: H) structures. The Al, unhydrogenated (a-Si) and hydrogenated (a-Si:H) precursor layers were deposited by RF magnetron sputtering. The structures prepared were annealed in forming gas (N2+5% H2) at atmospheric pressure for 6 h at 530°C. The structural properties of the poly-Si films were studied by Raman and X-ray diffraction spectroscopy and optical microscopy. Studies were performed of the influence of the substrate temperature of the a-Si:H precursor layers, Tsa-Si, and H2 pressure during the sputtering, η, on the structure of the poly-Si films obtained. It was shown that the grain size in the poly-Si films increases with Tsa-Si and η. The value of the tensile stress in the poly-Si films decreases with the increase of the substrate temperature of the a-Si (a-Si:H) precursor and the decrease of the H2 partial pressure.

Structural and optical properties of electrochemically deposited ZnO films in electrolyte containing Al2(SO4)3

The present work concerns the electrochemical deposition of aluminium doped ZnO nanostructured thin films on SnO2:F covered glass substrates. Doped with Al nanostructured ZnO (ZnO:Al) films are obtained by an electrochemical process using a three-electrode potentiostatic system with a saturated calomel electrode as reference electrode, in aqueous solution containing ZnCl2, KCl and Al2(SO4)3. The influence of the deposition parameters on the structural properties of the obtained ZnO:Al layers is investigated by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). Energy Dispersive X-ray Analysis (EDAX) is applied for measurement of the Al content in the films. The SEM micrographs and AFM pictures show that the ZnO:Al films consist of nanograins with a shape of walls. The XRD spectra demonstrate (100), (002), (101), (110) and (103) the characteristic reflexes of the ZnO. Influence of the Al concentration on the IR reflectance spectra and haze ratio of ZnO:Al thin films are presented and discussed.

I‐V characteristics of n‐ZnO/poly‐Si thin film heterostructure

ZnO has been extensively studied for many different applications, such as gas sensors, transparent conductive electrodes in solar cells and light emitting diodes, etc., because of its chemical stability and sensitivity to different adsorbed gases, amenability to doping, large energy gap, nontoxicity and low cost. ZnO thin films have been applied for device engineering in different heterostructures, as well. In this work the I‐V characteristics of two thin film heterostructures n‐ZnO/p‐poly‐Si with ZnO films with different thicknesses, 80 and 300 nm are studied. The ZnO polycrystalline films are deposited by RF sputtering in an atmosphere of Ar on the surface of a p‐type poly‐Si layer. The poly‐Si films are prepared on glass substrate by the method of Aluminum Induced Crystallization (AIC) from precursor layers of Al and a‐Si:H. The Al and a‐Si:H precursor films are deposited by magnetron sputtering on glass substrate. The a‐Si:H film precursors contain 9 at.% hydrogen. The isotermal annealing of the struc...

Deposition of Perylene Diimide Derivatives for Dye-Sensitized Solar Cells

The aim of this work is to examine the photosensitivity of dye-sensitized materials. Three types of organic dye sensitizers, i.e. perylene diimide (PDI) derivatives with different terminal groups were synthesized. The synthesized PDI derivates were deposited by dipping on a glass/ITO substrate covered with arrays of ZnO nanorods (NR) grown by an electrochemical process. An Ag grid contact was deposited on the PDI films on the stack glass/ITO/ZnONR/PDI; then I-V characteristics of the structures were measured in dark and under illumination with a halogen lamp. The photosensitivity of the different dye-sensitized materials is discussed.

Structural, Optical and Electrical Properties of ZnO Thin Films Doped with Al, V and Nb, Deposited by r.f. Magnetron Sputtering

Structural, optical and electrical properties of ZnO thin films doped with different elements (Al, Al + H, V, Nb), deposited by r.f. magnetron sputtering on glass substrates at different temperature Ts between 50 and 500 °C are studied. XRD spectra demonstrate a preferential (002) crystallographic orientation with the c-axis perpendicular to the substrate surface and grains sizes of about 19–29 nm. The value of band gap energy Eg is in the range of 3.49–3.58 eV for ZnO:Al, 3.51–3.58 eV for ZnO:Al:H, 3.44–3.47 eV for ZnO:V, and 3.28–3.44 eV for ZnO:Nb. The deposited ZnO films doped with Al, H, V and Nb have low resistivities of 1.6–2.2⋅10−3 Ωcm. The transparency of the studied films is about 85–90 % in the visible region. The obtained transparent conductive ZnO thin films can be applied in solar cells and other optoelectronic devices as TCO.

Room-temperature sensitivity to NO2 exposure of electrochemically-deposited nanostructured ZnO layers

This paper reports studies on the sensitivity of ZnO layers to NO2 exposure. ZnO layers were fabricated by electrochemical deposition on the surface of a quartz crystal microbalance (QCM) with Au electrodes. The sensitivity was estimated using the frequency-time characteristics of the QCM. For this purpose, the resonance frequency shift was measured. The sorption process was investigated in a NO2 gas flow. The change in the resonance frequency, f of the QCM as a function of the loaded mass of NO2 was followed for a NO2 concentration of 500 ppm. Under gas exposure, the frequency decreased and reached saturation in five min. A frequency shift of 38 Hz was measured and a mass loading of 8.39 ng was calculated. The resonance frequency showed a very good recovery within two minutes after the NO2 flow was switched off. The results demonstrate that the electrodeposited nanostructured ZnO layers have a potential for application as NO2 gas sensors.

Influence of annealing on the optical, structural and electrical properties of ZnO:Al/Ag/ZnO:Al multilayer stack structures

Multilayer stack structures ZnO:Al(20 nm)/Ag(x)/ZnO:Al(20 nm) with different thickness of the middle Ag(x) layer – x = 6 nm, 10 nm, 12 nm, 16 nm and 20 nm, were prepared by r.f. magnetron sputtering. The ZnO:Al and Ag layers were deposited by magnetron sputtering on glass substrates without heating. The two-layer structures ZnO:Al(20)/Ag(x) were annealed in N2 + H2 at 180 °C, 50 min., and then capped by the top ZnO:Al(20 nm) layer. The optical, structural and electrical properties were studied of the as-deposited and of the annealed three-layer stacks. The TEM, SEM and AFM analyses demonstrated changes of the stack structure with the Ag film thickness and after annealing. The transmittance and reflectance spectra revealed bands of Ag electrons plasma oscillations and inter-band d-shell Ag electrons which were red-shifted after annealing. The as-deposited structures had low resistivity (1×10−3 to 4×10−5 Ω cm), which decreased with the thickness of the Ag film due to the change in the carrier transport mechanisms. The value of the resistivity increased after annealing.