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Films of Sb-doped SnO2 were deposited by dip-coating technique. The morphology analysis showed that the microstructure of the samples exhibits many shaped nano-sized crystallites homogenously dispersed on the surfaces. The roughness varies with Sb-content, implying that doping has an important effect on the surface morphology of the films. Raman and FTIR-ATR investigations revealed that the films exhibit a vibration mode at 564 cm−1 ascribed to the amorphous phase overlapping the crystallites. Thus, the selection rule ( k = 0 ) is relaxed because of disorder and reduced crystallites size to nanoscale by Sb-doping, which may explain the broadening and shift of the lattice modes. The vibration of sub-bridging oxygen atoms seems to be significantly affected by oxygen vacancies and Sb-derived surface mode has been identified at 578 cm−1. The optical band gap is red-shift due to the introduction of localized states in the SnO2 bulk associated to Sb-doping and oxygen defects. The refractive index varies due the enhanced grain boundaries effect and surface disorder induced by Sb incorporation in the crystal lattice. The photoconductivity (σac) shows a dispersion pattern with two regions, corresponding to extrinsic and intrinsic conductivities. Under UV-illumination, the electrical charge transport mechanism changes from multi-hopping to single-hopping at higher temperatures.

Sb-doped SnO2 thin films synthesized by sol-gel method were characterized physically and electrochemically. The crystallization was promoted by Sb incorporation in the lattice and the optical gap is blue-shifted due to the quantum confinement. The thermal variation of the electrical conductivity indicates a semiconducting behavior with relaxation process shifted to higher frequencies, typical of hopping mechanism of charge carriers. The hopping length R averages ~ 1.4 nm and the maximum barrier height (Wm) for the electronic jumps is 878 meV. The interfacial capacitance is characteristic of n-type behavior with an electrons density of 2.7 × 1019 cm−3 and a space charge region of 150 nm. The valence and conduction bands were found to be −0.89 and +2.95 VSCE respectively; they are pH sensitive and sweeping with respect to redox system. The impedance data revealed three distinct electrochemical behaviors with high diffusion process in doped samples marked by the increase of Warburg impedance (0.91–202.3 kΩ·cm2). The optimal band bending with respect to levels (H2O/H2, O2/H2O) • ‐ (O2/O2• −, OH•/H2O), was achieved with localized states mediating the charge exchange.

In this work, we have studied the evolution of the potential barrier of ZnO/Si hetero-junction interface and we have experimentally highlighted an interface state defect that controls the conduction of the charge carriers. The samples were elaborated by DC reactive sputtering method, under controlled ambient mixture gas of Ar/O2. The study consists of the effect of the ZnO film thickness on the evolution of the potential barrier at the interface profile. The determination of the defects controlling the conduction is investigated by thermally stimulated current technique. The results showed that the electrical conduction is controlled by defects situated close to the conduction band of ZnO with activation energy of 0.35 eV. However, their density influences considerably both the rectification of n-ZnO/p-Si hetero-junction diode and the transport phenomena through the interface. Effectively, the current-potential-temperature measurements showed that when the thickness varied from 30 to 100 nm, the conduction mechanism at the n-ZnO/p-Si interface changed from tunneling through the potential barrier model to the diffusion over the potential barrier.

ZnO thin films were deposited by home-made DC sputtering of zinc target under mixed gases (Argon, Oxygen) plasma on glass substrates. Films were deposited by varying oxygen partial pressure (PO2) from 0.09 to 1.3 mbar in the deposition chamber, at a fixed substrate temperature of 100 °C. The samples were characterized by photoluminescence (PL), X-ray diffraction (XRD), optical transmissions (UV–vis), scanning electron microscopy (SEM) and electrical (Hall effect) measurements. The results indicate that by varying the oxygen pressure in the deposition chamber, the films show a precise and well defined photoluminescence emissions for each range of pressure covering almost the entire visible domain (UV, UV-Violet, Violet, Blue, and Red) with high intensities. Moreover, the deposited films have different defects levels. The XRD analysis indicates that the films are well grown along the c-axis peak, but with different crystalline quality. Optical measurements reveal a high transmission, up to 90%, in the spectral region between 400 and 2500 nm and a large variation of the optical band gap (3.16–4.34 eV). As an application of the deposited ZnO films, the photo-catalytic degradation of a synthetic solution of Rhodamine B (RhB) poured on a ZnO thin film was successfully achieved and an elimination rate of 38% was obtained after exposing the film to solar light for 3 h.

Undoped zinc oxide (ZnO) and indium-doped (ZnO:In) thin films were grown at different temperatures (250–400 °C) on alkali-free borosilicate glass and n-Si (100) substrates by Ultrasonic Spray Pyrolysis method. The structural, compositional, optical and electrical properties of ZnO films were investigated by X-ray diffraction, Scanning Electron Microscopy, Rutherford Back Scattering Spectroscopy, Fourier Transform Infrared spectroscopy, photoluminescence (PL) and the four-point probe technique. The predominance of ultraviolet (UV) and blue emission intensities was found to be closely dependent on the resistivity of the film. The visible emission band (peaking at 432 nm) prevails for low film resistivity, ranging from 10− 2 to 1 Ω·cm. By contrast, for higher resistivity (> 1 Ω·cm), there is a predominance of the UV band (382 nm). The PL and photoresponsivity results of fabricated ZnO:In/n-Si(100) heterojunctions prepared at different temperatures are discussed. The maximum spectral response of the ZnO:8%In/Si heterojunction diode fabricated at 250 °C was about 80 mA/W at zero bias. The highlighted results are attractive for the optoelectronic applications.

The undoped, Al-doped and In-doped ZnO thin films were deposited by ultrasonic spray pyrolysis technique, onto glass and p-Si substrates and the physical properties of the films were investigated. The X-ray diffraction, optical analysis and electrical characterisations, indicate that the films were polycrystalline with hexagonal wurtzite type structure and revealed that the aluminium doping deteriorates the crystalline and optical properties and enhances the electrical conductivity whereas indium doping improves all properties. The transport mechanism controlling the conduction through the heterojunctions was studied. For the heterostructures, the temperature dependent current–voltage characteristics showed rectifying behaviour in the dark, but current transport mechanism is not the same for all heterojunctions. Therefore, the presence of the interface states and volume defects are identified as limiting factors for obtaining a high quality heterojunction interface.

In this paper, we study structures contained thin hydrogenated amorphous silicon (a-Si:H) films deposited on porous silicon multilayers (Distributed Bragg Reflector DBR) formed by electrochemical etching of crystalline silicon (c-Si) wafers. The a-Si:H thin films were deposited by the Direct-current magnetron sputtering technique in a mixture of argon and hydrogen atmosphere. It is shown in our previous work that the Bragg mirrors formed on crystalline silicon play an important role in the light trapping in a-Si:H. The structural features of porous silicon, in terms of porosity, thickness and surface roughness, were determined using spectroscopic ellipsometry. The elaborated structures were analysed by impedance spectroscopy. The fit of data obtained from the impedance spectroscopy allowed us to determine the electrical equivalent circuit. This permits the identification of the electronic behaviour of the structures and allows us to explain the role of their different components, including the interfaces. For this purpose, we have proceeded successively. First, by the characterisation of porous silicon monolayers, afterward structures formed by porous silicon multilayers as DBR and structures of a-Si:H/c-Si and a-Si:H/PSi(DBR)/c-Si are characterised. A negative capacitance was found for the heterojunction with DBR, which was attributed to the existence of defect states at the interfaces between porous and amorphous silicon.

In this work, thin films of ZnO were deposited by DC reactive sputtering of zinc target under (Ar and O2) gas atmosphere, at a deposition temperature of 100 °C. A series of samples were prepared on both corning glass and p-doped crystalline silicon substrates, at different Ar flow rates (FAr) ranging from 0.5 and 2.5 sccm. The films properties were investigated by atomic force microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The results showed thin films with rough surfaces and polycrystalline structure. The electrical study (current-voltage characteristics) of ZnO/p-Si hetero-junctions revealed a rectification behavior. The highest forward current was obtained for FAr = 1.5sccm. The exposure at room temperature of ZnO/p-Si hetero-structures to ethanol vapors showed a high gas sensing response for ZnO/p-Si hetero-junctions with rough surface and high forward current, corresponding to FAr = 1.5 sccm. For a low concentration of ethanol vapor (10 ppm), the dynamic response at room temperature of ZnO/p-Si hetero-junctions revealed a sensitivity ranging from 40 to 80% with response and recovery times of 5 and 3 s respectively. Comparing these characteristics to those already obtained by other teams showed that the elaborated devices in this work are good candidates for fast sensors of low concentrations of ethanol vapors at room temperature.

It is known that the quality of the diode and the transport of the charge carriers across the junction may be greatly influenced by the quality of the interface, and depends on the crystallinity of thin layers. In this work, we have prepared the p-CuO/n-ZnO and p-CuO/n-ZnS hetero-junctions by ultrasonic spray pyrolysis at 300 °C under atmospheric pressure. We have investigated the influence of the thickness of CuO film on the electrical properties of the hetero-junctions. The X-ray diffraction indicates that both the CuO and ZnO thin films grow according to polycrystalline nature while ZnS films show a quasi-amorphous nature. The current voltage temperature ( I – V – T ) and capacitance voltage ( C – V ) characteristics reveal that CuO/ZnS is an abrupt junction, whereas the data of CuO/ZnO hetero-junctions suggest that the potential barrier heights are spatially non-uniform (junction not abrupt). The electrical behavior of the junction is strongly affected by the defect state distribution at the hetero-interface. The recombination process involving the interface states predominates at low forward bias ( V V >0.5 V) on the thin CuO side. The junction parameters (ideality factor, rectification ratio, built in potential etc…) are of the same order of magnitude for both heterojunction diodes i.e. ZnO/CuO and ZnS/CuO.

In this study we report on the photosensitivity of the electrical properties of a structure based on a thin film of hydrogenated amorphous silicon (a-Si:H) deposited onto a multilayer porous silicon (Bragg mirrors) formed in crystalline silicon (c-Si). We present the results obtained from dark and under illumination current–voltage (I–V) characteristics of Al/a-Si:H/PSi/c-Si structure. The aim of this study is to evaluate the influence of Bragg mirrors porous silicon at back-side on the electrical photosensitivity of a-Si:H. In this purpose, samples of monolayer and multilayer porous silicon have been formed in crystalline silicon by electrochemical etching method. The morphology and optical properties of monolayer samples have investigated by gravimetric analysis and reflectivity measurements, the Bragg mirrors are investigated by reflectivity measurements. The a-Si:H thin films were deposited by the DC magnetron sputtering technique in a mixture of argon and hydrogen atmosphere. These films were characterized by Fourier Transformed Infra Red spectroscopy and optical transmission. The I–V results obtained from dark show a decrease in current of Al/a-Si:H/PSi/c-Si structure compared with Al/a-Si:H/c-Si structure while there is enhancement of the photocurrent in the structure with Bragg mirrors back reflector. This result attests that the Bragg mirrors formed on crystalline silicon play an important role in the light trapping.

The present work is an investigation of the solution flow rate influence on copper oxide (CuO) thin film properties deposited by ultrasonic spray pyrolysis. A set of CuO thin films were deposited, with various solution flow rates, on glass substrate at 300 °C. The precursor solution is formed with copper salt dissolution in distilled water with 0.05 molarity. The solution flow rate was ranged from 10 to 30 ml/h. Films composition and structure were characterized by means of XRD (X Rays diffraction) and Raman scattering. The optical properties were studied using UV–visible spectroscopy. The electrical conductivity, carrier mobility and concentration were determined by Hall Effect measurements. The obtained results indicate that flow rate is a key parameter controlling CuO films growth mechanism and their physical properties. The prepared films are mainly composed with a CuO monophase, the crystallite size is reduced with increasing the flow rate. A ZnO/CuO heterojunction structure has been realized and its rectifying behavior is tested.

ZnO thin films, prepared by ultrasonic spray onto glass substrate, crystallize in the wurtzite structure. The XRD pattern shows preferential orientation along the [0 0 2] direction. The films deposited at 350 °C consist of 60 nm crystallites with an average thickness of ∼150 nm and SEM images show rough surface areas. The gap increases with increasing the temperature of the substrate and a value of 3.25 eV is obtained for films deposited at 350 °C. ZnO is nominally non-stochiometric and exhibits n-type conduction because of the native defects such as oxygen vacancies (VO) and/or interstitial zinc atom (Zni) which act as donor shallows. The conductivity is thermally activated and obeys to an exponential type law with activation energy of 57 meV and an electron mobility of 7 cm2 V−1 s−1. The capacitance-voltage (C−2 V) measurement in acid electrolyte (pH ∼ 3) shows a linear behavior with a positive slope, characteristic of n-type conduction. A flat band potential of −0.70 VSCE and a donors density of 5.30 × 1016 cm−3 are determined. The Nyquist plot exhibits two semicircles attributed to a capacitive behavior with a low density of surface states within the gap region. The centre is localized below the real axis with a depletion angle of 16° ascribed to a constant phase element (CPE) due to the roughness of the film. The energy band diagram assesses the potentiality of ZnO films for the photo-electrochemical conversion. As application, 94% of chromate (3.8 × 10−4 M) is reduced after 6 h under sunlight (AM 1) with a quantum yield of 0.06% and the oxidation follows a first order kinetic.

Heterojunction structures of n-ZnO/p-Si were prepared by growing undoped ZnO thin films onto p-type Si (1 0 0) substrates. ZnO films were deposited by ultrasonic spray method. The structural and optical properties of ZnO films were studied as a function of substrate temperature. The X-ray diffraction measurements showed that ZnO film has a nanocrystalline structure with (0 0 2) preferential orientation and grain sizes ranging from 25 to 70 nm. An increase in the deposition temperature enhances the (0 0 2) diffraction peak intensity. The transmittance measurements in the UV–vis wavelengths range indicated that the films optical gap increases with increase in substrate temperature. The heterojunction parameters were evaluated from the current–voltage (IV) and capacitance–voltage (CV) measurements carried out on the realized n-ZnO/p-Si heterostructure, in dark at different temperatures. From these measurements we inferred that the forward conduction is dominated by multi-step tunneling current at low bias voltage in the 0.2–0.5 V region. The ideality factor of the obtained heterojunction is larger than 2, the activation energy of saturation current is about 0.14 eV and the junction built-in potential deduced from C–V measurements is equal to 1.14 V at room temperature.

In the present work, zinc oxide (ZnO) thin films are deposited by the ultrasonic spray method. In order to study the influence of the nature of the precursor solution, zinc acetate and zinc nitrate salts dissolved in methanol are used respectively to prepare two non-aqueous starting solutions. The influence of substrate temperature on the structural growth kinetics and optical properties of ZnO films is also investigated. For this purpose, the substrate temperature is varied in the range of 250—400°C. X-ray diffraction (XRD) analysis reveals that at low temperature the films that are grown contain nanocrystallites with a privileged orientation depending on the nature of the starting precursor; these privileged orientations correspond to the plane (100) for the films deposited with zinc acetate and (002) for films prepared with zinc nitrate precursor. However, with increasing deposition temperature, the privileged orientation disappears. The growth kinetics is closely related to the substrate temperature and to the nature of the starting solution. The scanning electron microscopy (SEM) observations suggest that the liquid droplets react once they reach the substrate surface when zinc acetate precursor is used. However, in the case of zinc nitrate solution, the droplets spread first on the substrate surface followed by the subsequent surface reaction. This difference is explained in terms of the dissociation enthalpy of both solutions.

Experimental analysis of current –voltage and capacitance-voltage characteristics of n-ZnO/p-Si (100) heterostructures were presented. Undoped and In-doped ZnO films were deposited by the simple ultrasonic spray method on p-Si substrates (100) at varied substrate temperatures from 200 to 400°C. The structural and optical properties of ZnO films were investigated using X-ray diffraction (XRD) and transmission spectra respectively. The electrical conductivity is calculated from transport measurement in a two probes coplanar structure. It is found that the doped ZnO: In films have higher (002) diffraction peak than undoped ZnO. All films exhibit a high transparency about 85%. The maximum conductivity is observed at 350°C for doped films but increases with substrate temperature for undoped ones. Current–voltage (I-V) characteristics of all n-ZnO/p-Si heterojunctions exhibit non linear characteristics with a small current leakage in the reverse voltage. The obtained device shows a barrier height in the order of 0.65 eV, this is consistent with the theoretical value 0.67eV. The capacitance increases with increasing reverse bias in an approximately linear 1/C2-V relationship.