S. Kahraman

Effect of heat treatment on the properties of Cd(OH)2 and CdO films grown by chemical bath deposition

Nanostructured cadmium hydroxide (Cd(OH)2) thin films have been fabricated on glass substrates by the chemical bath deposition method and converted into cadmium oxide (CdO) films by heat treatments. Some of the films were studied as-grown and the others were annealed in air at 150, 300 and 450 °C. The effects of various annealing processes on the structural, morphological and optical properties of the Cd(OH)2 and CdO films were studied. The band gaps of the films vary from 2.74 eV to 2.32 eV for different annealing temperatures. It was observed that there is a direct dependence of the structural, morphological and optical properties on the annealing temperature of the films. X-ray diffraction (XRD) measurements showed that as-grown and annealed film at 150 °C fully consist of Cd(OH)2 and the annealed films at 300 and 450 °C consist of CdO nanoparticles. The size of the nanoparticles, which were calculated from the scanning electron microscopy (SEM) figures by using a pixels program, was found to lie between 460 and 600 nm.

Polyethylene glycol-assisted growth of Cu2SnS3promising absorbers for thin film solar cell applications

In this paper, we report, for the first time, the results of the polyethylene glycol- (PEG) assisted preparation and characterization of high-quality and well-crystallized Cu2SnS3 (CTS) thin films obtained using sol–gel spin-coating method and a subsequent annealing in a sulphur atmosphere. Structural, morphological, compositional, electrical and optical investigations were carried out. The X-ray diffraction patterns of the samples proved the polycrystalline nature and preferred crystallization of the films. No peak referring to other binary or ternary phases were detected in the patterns. The intensity of the preferred orientation and crystallite size of the films increased with increasing PEG content. This trend yielded an improvement in photo-transient currents of the PEG-assisted growth of CTS films. The scanning electron microscopy images revealed that the CTS films have continuous, dense and agglomeration-like morphology. Through energy dispersive X-ray spectroscopy studies, it has been deduced that the samples consist of Cu, Sn and S of which atomic percentages were consistent with Cu/Sn and S/metal initial ratios. The agglomerated morphology of the samples has been attributed to increasing PEG content. A remarkable enhancement was observed in photo-transient currents of p-n junction of the produced films along with increasing PEG content. Through resistivity-temperature measurements, three impurity level electrical activation energy values for each film were found. Optical band gap values of the films were estimated via absorbance-wavelength behaviours and decreased with increasing PEG content. It has been revealed that PEG-assisted growth of CTS thin films is a promising way to improve its photovoltaic characteristics.

Characterisation of ZnO nanorod arrays grown by a low temperature hydrothermal method

In this paper, growth steps of well defined ZnO nanorod arrays deposited on seeded substrates were investigated. To obtain ZnO seed layer on glass substrates, a successive ionic layer adsorption and reaction (SILAR) method was used and then ZnO nanorods were grown on seed layer using a chemical bath deposition (CBD) method. The effects of seed layer and deposition time on morphology, crystallographic structure (e.g. grain size, microstrain and dislocation density) and electrical characteristics of ZnO nanorods were studied. From the SEM micrographs, it could be seen that the ZnO nanorods densely covered the substrate and were nearly perpendicular to the substrate surface. The XRD patterns showed that the ZnO nanorod arrays had a hexagonal wurtzite structure with a preferred orientation along the (002) plane. An increase in deposition time resulted in an increase in the intensity of the preferred orientation and grain size, but a decrease in microstrain and dislocation density. Electrical activation energies of the structures were calculated as 0.15–0.85 eV from current–temperature characteristics. It was concluded that the morphologies of the structures obtained in this study via a simple and fast solution method can provide high surface areas which are important in area-dependent applications, such as solar cells, hydrogen conversion devices, sensors, etc.

Cu2SnS3 absorber thin films prepared via successive ionic layer adsorption and reaction method

Abstract In this paper, we report the production of Cu2SnS3 thin films with high phase purity via successive ionic layer adsorption and reaction method on soda lime glass substrates. Structural, morphological, compositional, optical and electrical investigations were carried out. The X-ray diffraction patterns of the samples matched very well with the reference pattern and proved the polycrystalline nature of the films. As a secondary phase, one weak peak indicating covallite Cu2–xS phase was observed in the pattern of the sample deposited by using equimolar Cu and Sn. The surface morphologies of the films were found to be continuous and composed of homogeneously distributed large grains. From the reflectance and transmittance data, the optical absorption coefficient values of the films were found to be about 104 cm−1 and the films were found to be almost opaque in the wavelengths from 200 to 600 nm with a small reflectivity of about 10%. Band gap values of the films decreased from 1.45 to 1.35 eV with decreasing Cu content. Electrical characterization showed that the films were p-type semiconductor. Two different impurity levels for each film were found via resistivity-temperature characteristics.

A novel study on ZnO nanostructures: coumarin effect

This novel study reports the behaviour of coumarin during the ZnO chemical bath deposition (CBD) process. Scanning electron microscopy studies revealed that grain sizes of the ZnO nanostructures get smaller and become more uniform in size with increasing coumarin content. Length-to-diameter ratio of the structures increased with the incorporation of coumarin. From the X-Ray diffraction results, with increasing coumarin content, significant decrease in grain sizes was determined. It was found that resistivity values of the structures increased with increasing coumarin content. This increase is attributed with a decrease in carrier concentration originated by carrier traps at the grain boundaries. Through slopes of versus curves, impurity level ionization energy values were calculated as 0.16, 0.06 eV; 0.11, 0.02 eV; and 0.08, 0.06 eV for the structure growth in the solutions containing 0, 1 and 5 at.% coumarin, respectively.

Growth and Characterization of CuO Nanostructures on Si for the Fabrication of CuO/p-Si Schottky Diodes

CuO interlayers in the CuO/p-Si Schottky diodes were fabricated by using CBD and sol-gel methods. Deposited CuO layers were characterized by SEM and XRD techniques. From the SEM images, it was seen that the film grown by CBD method is denser than the film grown by sol-gel method. This result is compatible with XRD results which show that the crystallization in CBD method is higher than it is in sol-gel method. For the electrical investigations, current-voltage characteristics of the diodes have been studied at room temperature. Conventional I-V and Nordes methods were used in order to determine the ideality factor, barrier height, and series resistance values. It was seen that the morphological and structural analysis are compatible with the results of electrical investigations.

Characterization of Al/n-ZnO/p-Si/Al structure with low-cost solution-grown ZnO layer

We report the fabrication of Al/n-ZnO/p-Si/Al diode structures with a flower-like ZnO layer. The average grain size, microstrain and dislocation density in the ZnO layer were determined as 25 nm, 1.55 × 10−3 and 3.23 × 1013 cm−2, respectively. From absorption spectra, the optical band gap was found to be ∼3.17 eV. A red shift was attributed to non-stoichiometry arising from Zn+2 ions substituting for oxygen vacancies. The ideality factor was determined as 1.55. The barrier height was calculated as 0.71 eV from I–V characteristics and 0.73 eV using the Norde plots.

CBD grown ZnO nanostructures: effects of solution temperature

In the present study, textured and highly oriented nano-structured ZnO films were synthesized via chemical bath deposition. The effects of solution temperature have been investigated. It is concluded that the solution temperature is crucial to the crystallography, morphology, electrical and optical behaviors of the ZnO films. X-ray diffraction studies and scanning electron microscopy observations revealed that the structures grown at 95°C had a large aspect ratio, a faster c-axis growth and better vertical orientation than those obtained at relatively lower temperature. The variations depending on solution temperature have been provisionally explained theoretically. Electrical resistivity and activation energies of the films decreased with increasing solution temperature. The variation was attributed to enhancement in the crystallographic structure with increasing growth temperature and to delocalized phonon states. Through the optical absorption spectra a red shift was observed and attributed to crystal defects, non-stochiometry that Zn+2 ions substitute oxygen vacancies and delocalized phonon states.