Hydrogenation and annealing effect on electrical properties of nanostructured Mg/Mn bilayer thin films

Bilayer Mg/Mn thin films have prepared using thermal evaporation method at pressure 10⁻⁵ torr. Hydrogenation process has been done on pristine and annealed bilayer structure of films at different hydrogen pressure for half an hour. In case of annealed samples partially semiconductor nature is observed and conductivity of films found to decrease with hydrogen pressure and increased with annealing temperature. The XRD analysis shows microcrystalline nature of as-deposited films and after annealing it produce crystalline nature. After hydrogenation an additional peaks of magnesium hydride are also observed that suggesting the presence of hydrogen and hydrogen storage capacity of thin film bilayer structure. Optical band gap of annealed bilayer thin films found to increase with hydrogen pressure. It means hydrogenation process is capable to change bilayer structure from metallic to semi-conducting. The variation in relative resistivity is found nonlinear with time and increases with hydrogen pressure, due to the net effect of hydrogen absorption. Raman spectra show the decrease in intensity of peaks with hydrogen pressure that confirm the presence of hydrogen. Optical photographs are taken in reflection mode that shows a change of color from brown to dark black state with increasing hydrogen gas pressure. This dark black state may be used as solar thermal energy collector because black body is good absorber of heat.     

Plasma-enhanced chemical vapour-deposited silicon nitride films; The effect of annealing on optical properties and etch rates

The optical properties and etch rates of silicon nitride (SiN_x:H) deposited by plasma-enhanced chemical vapour deposition (PECVD) and their correlation with bond concentrations have been studied. By varying the silane-to-total gas ratio, films with refractive index (n) between 1.92 and 3.00 were deposited. Higher n films had increased absorption and decreased etch rates. Annealing the samples at different temperatures revealed that all films were thermally stable up to 750 °C, above which all experienced a rise in n, attributed mainly to mass densification. The etch rate correlated well the N–H bond concentration for both annealed and as-deposited films.     

Hydrogen effect on the optical and electrical properties of metal oxide and nitride thin films

Effect of hydrogen introduction into some metal oxide and nitride thin films was examined. Modification of electrical and optical properties by hydrogen introduction was examined on SnO₂${}_2$, Sn–GeO₂${}_2$, Ge–CdO₂${}_2$, ZnO. Electrical resistance could be reduced in some films without loosing their transparence to the visible light. Hydrogen introduction to Cu₃${}_3$N changed the film an electrical conductor. Films of AlN and TiN were rather insensitive to the hydrogen introduction; the hydrogen effect was only observed when the nitrides contain some imperfection in the compounds.     

Influence of silane flow on structural, optical and electrical properties of a-Si:H thin films deposited by hot wire chemical vapor deposition (HW-CVD) technique

The electrical, structural and optical properties of hydrogenated amorphous silicon (a-Si:H) films deposited from pure silane (SiH₄) using hot wire chemical vapor deposition (HW-CVD) technique are systematically studied as a function of silane flow rate between 5 and 30 sccm. We found that the properties are greatly affected by the silane flow rate over the range we studied. The device quality a-Si:H films with a photosensitivity >10⁵ were deposited by HW-CVD at a deposition rate >10 Å s⁻¹ using low silane flow rate. However, a-Si:H films deposited at higher silane flow rate and/or higher deposition rates show degradation in their structural and electrical properties. The FTIR studies indicate that the hydrogen bonding in a-Si:H films shifts from mono-hydrogen (Si–H) to di-hydrogen (Si–H₂) and (Si–H₂)_n complexes when films were deposited at higher silane flow rate. The hydrogen content in the a-Si:H films increases with increase in silane flow rate and was found to be less than 10 at.%. The Raman spectra show increase in disorder and the Rayleigh scattering with increase in silane flow rate. The optical band gap also shows an increasing trend with silane flow rate. Therefore, only the hydrogen content cannot be accounted for the increase in the optical band gap. We think that the increase in the optical band gap may be due to the increase in the voids. These voids reduce the effective density of material and increase the average Si–Si distance, which is responsible for the increase in the band gap. Silane flow rate of 5 sccm, appears to be an optimum flow rate for the growth of mono-hydrogen (Si–H) bonded species having low hydrogen content (4.25 at%) in a-Si:H films at high deposition rate (12.5 Å s⁻¹), high photosensitivity (10⁵) and small structural disorder.     

RF magnetron sputtered ZnO:Al thin films on glass substrates: A study of damp heat stability on their optical and electrical properties

ZnO:Al thin films were deposited on glass substrates by RF magnetron sputtering from a powder compacted ceramic target. Structural, electrical and optical properties of the films with different thickness were characterized. The damp heat stability of ZnO:Al thin film was investigated for its application in thin-film solar cells. After the 1000 h damp heat treatment in harsh conditions of 85% relative humidity at 85 °C for all samples, a degradation of electrical properties was observed, while the transmissions of the films were almost unchanged. Thick films with a relative large grain size could form compact structure to resist the corrosion by oxygen and water molecules.     

The effect of annealing temperature on the electrochromic properties of nanostructured NiO films

The nickel oxide (NiO) films have been prepared by sol-gel dip coating route. They were treated at different temperatures ranging from 250 to 450 °C at an optimum number of layers (8 layers) on a conducting substrate (FTO) and glass plate. The X-ray diffraction (XRD) spectrum reveals that the crystallanity increases along the planes (1 1 1), (2 0 0) and (2 2 0) and the crystallite size increases from 7 to 26 nm as the temperature increased from 250 to 450 °C. The FTIR spectrum confirms the formation of Ni-O bond. The SEM images indicate the formation of nanorods in the temperature range 350-450 °C. The electrochromic properties have been studied using cyclic voltammetric (CV) and chronoamperometric (CA) techniques. The Ni(II)/Ni(III) transformation is the possible cause for the reversible colour change from transparent to dark brown. The film prepared at 300 °C with a thickness of 306 nm exhibits maximum anodic/cathodic diffusion coefficient of 11×10⁻¹² cm²/s/6.44×10⁻¹² cm²/s and the same film exhibits the maximum colour change of 68% with a photopic contrast ratio of 5.17. The chronoamperogram reveals that the colouration/decolouration response time decreases with the increase in preparation temperature. The films treated at 300 °C exhibit the optimum electrochromic behaviour.     

a-Si:H薄膜的再结晶技术发展概述

论述了非晶硅薄膜的主要再结晶技术，包括传统的炉子退火、金属诱导晶化、微波诱导晶化、快速热退火和激光晶化。着重指出了各种晶化技术已取得的研究成果、优缺点、有待进一步研究的内容及其在多晶硅薄膜太阳电池工业生产中的应用前景。     

Studies on optical and electrical properties of SILAR-deposited CuO thin films

CuO thin films prepared by SILAR technique using aqueous solutions of various pH values and their characterization are presented in this report. The pH dependence on structural, morphological, optical and electrical properties of the prepared films is studied. Thickness of films is found to vary in between 0.52 and 0.82 µm. Microstructural parameters such as crystallite size, strain and dislocation density of the film have been evaluated. The crystallographic behaviour of the film has shown that all the coated thin films are in monoclinic structure with (002) preferred orientation. The size of the crystallites is found to increase with the pH values. Surface morphological behaviour of the films prepared using different pH values are analysed. Optical properties of the films were analysed from absorption and transmittance studies of CuO thin films. Band gap energy values of CuO thin films have been found to decrease from 2.12 to 1.91 eV with increasing pH values of the solution. The thin film formed at a solution pH 11 has shown least resistivity and high carrier concentration. The I-V characteristics of n-Si/p-CuO heterojunction under 200-watts halogen lamp illumination show open-circuit voltage of ~ 0.37 V and short-circuit current of ~1.02 × 10^?6 A.     

Hydrogenation effect on structural,electrical and optical properties of CdS thin films for solar cell

Adsorption effects would be expected to be of considerable importance with thin films because of the changes in electron location accompanying adsorption. The effects of hydrogenation on structural, optical and electrical properties of the CdS thin films have been reported. GIXRD patterns shows that films have polycrystalline nature with a hexagonal structure. The optical band gap increased after hydrogenation of the film. The variation of conductivity of CdS films have been investigated depending upon the applied voltage at room temperature. The resistivity increased after hydrogenation of the films. Hydrogenated thin films can be used in solar cells because hydrogen plays an important role to modify the physical properties.     

The effect of target erosion and RF substrate biasing on the properties of reactively sputtered ITO films

ITO films with excellent electrical and optical properties may be produced at relatively high rates by dc magnetron sputtering with and without ion-plating techniques, when the deposition parameters have been properly adjusted. It is reported here, however, that the degree of target erosion affects dramatically the quality of the deposited ITO films. According to the experimental results presented and a simple qualitative model, the observed effect may be attributed to the changing magnetic field strength at the active are of the magnetron head. Pratical ways of overcoming this problem of reproducibility in the properties of ITO films are also discussed.     

Electrical properties of a-Si:H thin films as a function of bonding configuration

Hydrogenated amorphous silicon (a-Si:H) thin films were fabricated by Radio Frequency (RF) magnetron sputtering. For solar-cell applications, a-Si:H layers are required to show low dark conductivity and high photoconductivity and, thus, high photosensitivity. Hydrogen flow ratio and working pressure were mainly adjusted to control bonding configurations and hydrogen concentration in the films. At a high working pressure of 12 mTorr, all of the prepared amorphous and microcrystalline silicon films showed a dominant IR absorption peak at 2100 cm⁻¹, which indicates a Si-H₂ stretching mode, grain boundaries and microvoids. When the working pressure was decreased to as low as 3 mTorr with a hydrogen flow ratio of 0.1, the bonding configuration of the films was mainly Si-H as determined by the dominant IR absorption peak at 2000 cm^−1, and the photosensitivity of the films was maximized to 760.     

Influence of laser scribing in the electrical properties of a-Si:H thin film photovoltaic modules

The third (P3) laser patterning step of thin film photovoltaic devices is studied experimentally using a diode pumped solid state laser with 532 nm wavelength and a delay generator. The effect on the electrical characteristics of the devices due to the patterning process is investigated by performing scribes on single, thin-film solar cells. As it is shown, in this type of experiments the inertia in the motion systems or in the scanner controlling the direction of the laser beam plays a critical role in the results. By controlling externally the output of the laser beam it is possible to overcome the inertia and investigate the real effect of the P3 laser scribing on the device electrical characteristics. When the laser scribing conditions are optimized and the inertia in the system is taken care of, the P3 process has very little effect on the device electrical characteristics. Translated to modules this means that by optimizing the P3 process, the decrease in the efficiency found when up-scaling from single cells to modules can be minimized (as far as the P3 process is concerned) to that coming from the removed area.     

The electrochromic properties of sputtered nickel oxide films

Electrochromic nickel oxide films were prepared by reactive RF sputtering from a nickel target in an oxygen atmosphere. The films were deposited as a compact 40 nm layer of trivalent nickel oxide, Ni₂O₃. Reduction and oxidation of the films in 1 M KOH resulted in bleaching and coloration, respectively. Voltammetry indicated that the eventual electrochromic reaction involved the β-Ni(OH)₂/β-NiOOH couple. In situ visible spectra showed electrochromic modulation of the transmittance throughout the visible range with a peak change in transmittance of about 60% at a wavelength of 500 nm. In situ spectra in the near-infrared region indicated improved electrochromic switching in this region; the sputtered nickel oxide film exhibited about a 30% change in transmittance in comparison to less than 10% for a similar electroprecipitated nickel hydroxide film. The sputtered nickel oxide films exhibited durable electrochromic switching for over 2500 coloration/bleaching cycles, a significant improvement over the less than 500 switching cycles exhibited by electroprecipitated nickel hydroxide films.     

Electrical conductivity in a-Si:H:Cl films

The temperature dependence of the electrical conductivity was investigated in chlorinated and hydrogenated amorphous silicon films (a-Si:H:Cl) deposited by glow discharge in the SiCl₄SiH₄ mixtures. The influence of chlorine on the different transport processes is determined according to the investigated temperature range. On the base of the experimental results and the speculative considerations regarding the film structure the inference is drawn that chlorination of hydrogenated amorphous silicon causes a decrease in the gap state density and an increase in the structural disorder. It is supposed that a more definite improvement of the electronical properties of glow discharge amorphous silicon could be expected for the relatively low chlorine concentration of about (1.0–2.0)×10²¹ at/cm³.     

Discharge power dependence of structural, optical and electrical properties of DC sputtered antimony doped tin oxide (ATO) films

Antimony doped tin oxide (ATO) is a transparent conducting oxide (TCO), which has been the focus of intensified study due to its wide range of technological applications and low cost. In the present work ATO films have been prepared by reactive DC magnetron sputtering from a metallic target at different discharge power densities without direct substrate heating. Then a post-deposition annealing at 350 °C in N₂ during 20 min was performed. There is a process window for the optimal sputter deposition of ATO with a minimum resistivity of about 3.3×10⁻³ Ω cm observed in samples deposited at a power density of 1.13 W/cm². These samples, which present a (2 1 1) preferential orientation, have good electrical conductivity and good transparency in the visible range. Higher values of sputtering discharge power density (1.24 W/cm²) change the preferential orientation to (1 0 1) because of the formation of oxygen vacancy planes. These samples are less conductive and transparent because their layered structure reduces the free charge mobility and allows the formation of Sb in its unusual oxidation state 4+ (between Sb³⁺ and Sb⁵⁺), which produces a sample blue darkening. Higher discharge power densities, above 1.41 W/cm², produce amorphous samples and an abrupt resistivity increase. The aim of the present work is to go into more depth in the knowledge of ATO in order to develop thin films with optimal electrical and optical properties.     

Temperature effect on the electrical and optical properties of indium-selenide thin-films

Indium-Selenide thin-films have been prepared by the thermal-evaporation technique at a pressure of 4.5×10⁻⁶ torr and a temperature of 673–873 K. For both the as-deposited and annealed films, (i) the electrical conductivity increased with increasing temperature and (ii) the variation of activation energy follows the island structure theory. The temperature co-efficient of resistance (T.C.R.) and Hall-effect measurements indicate that the sample is a n-type carrier. The optical spectra for both types of films were obtained in the wavelength range 0.3<λ<2.5 μm, and by comparing the magnitude of transmittance spectra, it is found that the annealed films are more transparent than the as-deposited ones in the UV and visible range. The integrated transmittance and reflectance values were obtained: the high values of T_lum and T_sol for the annealed films suggest that indium selenide may be used in selective-surface devices.     

Performance of double junction a-Si solar cells by using ZnO:Al films with different electrical and optical properties at the n/metal interface

High-quality ZnO:Al films have been prepared by using RF-magnetron-sputtering method with resistivity ranging from 10⁻¹ to 10⁻⁴ Ω cm and transmittance above 90% in visible region. We have fabricated small area (1 cm²) double junction (a-Si/a-Si) solar cells using ZnO/Al and ZnO/Ag as back contact. The conversion efficiency of double junction a-Si solar cell increases from 9.9% to 10.9% by using ZnO/Al back contact and to 11.4% by using ZnO/Ag as back contact. Effect of variation of thickness of i-layer on performance of the cell has also been studied.     

Influence of dysprosium doping on the electrical and optical properties of CdO thin films

Lightly Dy-doped CdO thin films (molar 0.5%, 1%, 2%, and 2.5%) have been prepared by a vacuum evaporation method on glass and Si wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV-vis-NIR absorption spectroscopy, and dc-electrical measurements. Experimental data indicate that Dy³⁺ doping slightly stretchy-stresses the CdO crystalline structure and changes the optical and electrical properties. The bandgap of CdO was suddenly narrowed by about 20% due to a little doping with Dy³⁺ ions. Then, as the Dy doping level was increased, the energygap was also increased. This variation was explained by the effect of Burstein-Moss energy shift (or bandgap widening effect) together with a bandgap shrinkage effect. The electrical behaviour of the samples shows that they are degenerate semiconductors. However, the 2% Dy-doped CdO sample shows an increase in its mobility by about 3.5 times, conductivity by 35 times, and carrier concentration by 10 times relative to undoped CdO film. From transparent conducting oxide point of view, Dy is sufficiently effective for CdO doping.     

Effect of rapid thermal annealing on optical properties of zinc sulphide thin films

Zinc sulphide (ZnS) thin films were prepared on clean surface glass substrates by thermal evaporation under pressure of 10^?5?Torr. Thickness of thin films was uniform 55?nm measured by ellipsometry. These films were also kept into a quartz glass tube for rapid thermal annealing at 30 and 60?s by using a 500?W halogen lamp for crystalline the structure. The cubic structure of the films was verified by X-ray diffraction and the intensity of predominant peak increases with annealing time. The optical absorption study was carried out by UV–ViS–NIR spectrometer in the range of 200–800?nm. The optical band gap changes from 3.48 to 3.08?eV, with rapid thermal annealing. Thermo electric power studies confirm the n-type nature of ZnS thin films and thermoelectric power increases with increase in temperature. This study is important because ZnS is potentially important material for antireflection coating and window layer material in hetero-junction solar cells.     

Temperature effect on the electrical properties of undoped NiO thin films

Undoped NiO thin films have been prepared onto glass substrate by e-beam evaporation of the element Ni in vacuum at 2 × 10⁻⁴ Pa. The as-deposited Ni films were then oxidized in air by heating about 2 h at a temperature of 470 K and then the oxidized Ni films are turned into NiO thin films. From the deposition time and film thickness after annealing in air, an effective deposition rate of NiO thin films was about 6.67 nms⁻¹. X-ray diffraction (XRD) study shows the NiO films are amorphous in nature. SEM studies of the surface morphology of NiO films exhibit a smooth and homogeneous growth on the entire surface. The elemental composition of NiO films is estimated by Energy Dispersive Analysis of X-rays (EDAX) method. The effects of temperature on the electrical properties of NiO thin films were studied in details. The heating and cooling cycles of the samples are reversible in the investigated temperature range after successive heat-treatment in air. Thickness dependence of conductivity is well in conformity with the Fuchs–Sondheimer theory. Temperature dependence of electrical conductivity shows a semiconducting behavior with activation energy. The thickness dependence of activation energy as well as thermopower studies was done within 293–473 K temperature range, respectively. Thermopower study indicates the NiO films a p-type semiconductor. Optical study in the wavelength range 0.3 < λ<1.2 μm range exhibits a high transmittance in the visible as well as in the near infra-red. Calculation from the optical data, the NiO sample exhibits a band gap at 3.11 eV, which does agree well with earlier reported values. These studies may be of importance for the application of this material in energy efficient surface coating devices.