M. Altunbaş

Bio: M. Altunbaş is an academic researcher from Karadeniz Technical University. The author has contributed to research in topics: Thin film & Annealing (metallurgy). The author has an hindex of 20, co-authored 40 publications receiving 1013 citations.

The effects of zinc nitrate, zinc acetate and zinc chloride precursors on investigation of structural and optical properties of ZnO thin films

Abstract: ZnO thin films were prepared using zinc chloride, zinc acetate and zinc nitrate precursors by spray pyrolysis technique on glass substrates at 550 °C. Structural and optical properties of ZnO films were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical transmittance spectra. Regardless of precursors, ZnO thin films are all in hexagonal crystallographic phase and have (0 0 2) preferred orientation. SEM images show completely different surface morphologies for each precursor in ZnO thin films. ZnO rod was observed only for zinc chloride precursor. The optical measurements reveal that films have a low transmittance and a direct band gap approximately 3.30 eV, which is very close to band gap of intrinsic ZnO.

Structural, optical and electrical properties of Al-doped ZnO microrods prepared by spray pyrolysis

Abstract: Al-doped ZnO thin films were obtained on glass substrates by spray pyrolysis in air atmosphere. The molar ratio of Al in the spray solution was changed in the range of 0–20 at.% in steps of 5 at.%. X-ray diffraction patterns of the films showed that the undoped and Al-doped ZnO films exhibited hexagonal wurtzite crystal structure with a preferred orientation along (002) direction. Surface morphology of the films obtained by scanning electron microscopy revealed that pure ZnO film grew as quasi-aligned hexagonal shaped microrods with diameters varying between 0.7 and 1.3 μm. However, Al doping resulted in pronounced changes in the morphology of the films such as the reduction in the rod diameter and deterioration in the surface quality of the rods. Nevertheless, the morphology of Al-doped samples still remained rod-like with a hexagonal cross-section. Flower-like structures in the films were observed due to rods slanting to each other when spray solution contained 20 at.% Al. Optical studies indicated that films had a low transmittance and the band gap decreased from 3.15 to 3.10 eV with the increasing Al molar ratio in the spray solution from 0 to 20 at.%.

Structural, optical and magnetic properties of Cr doped ZnO microrods prepared by spray pyrolysis method

Abstract: A series of Cr-doped ZnO micro-rod arrays were fabricated by a spray pyrolysis method. X-ray diffraction patterns of the samples showed that the undoped and Cr-doped ZnO microrods exhibit hexagonal crystal structure. Surface morphology analysis of the samples has revealed that pure ZnO sample has a hexagonal microrod morphology. From X-ray photoelectron spectroscopy studies, the Cr 2p3/2 binding energy is found to be 577.3 eV indicating that the electron binding energy of the Cr in ZnO is almost the same as the binding energy of Cr 3+ states in Cr 2 O 3 . The optical band gap E g decreases slightly from 3.26 to 3.15 eV with the increase of actual Cr molar fraction from x = 0.00 to 0.046 in ZnO. Photoluminescence studies at 10 K show that the incorporation of chromium leads to a relative increase of deep level band intensity. It was also observed that Cr doped samples clearly showed ferromagnetic behavior; however, 2.5 at.% Cr doped ZnO showed remnant magnetization higher than that of 1.1 at.% and 4.6 at.% Cr doped samples, while 4.6 at.% Cr doped ZnO samples had a coercive field higher than the other dopings.

Structural, optical and magnetic properties of Cd1−xCoxS thin films prepared by spray pyrolysis

Abstract: Structural, optical and magnetic properties of CdS thin films with the addition of Co prepared by (i) spray pyrolysis of Cd1−xCoxS (x⩽0.10) thin films (Type 1) and (ii) Co diffusion doped CdS films (Type 2) were investigated. The undoped film has a hexagonal structure with a strong (1 1 2) preferred orientation. As the Co concentration in CdS is increased, the preferred orientation changes from (1 1 2) to (0 0 2) direction. X-ray photoelectron spectroscopy (XPS) analysis shows that Co atoms on the surface of films are found to be bounded either to S atoms or O atoms. Although most of the bindings of Co atoms include Co–O bondings, some of them replace the Cd atoms by making chemical bounds with S atoms. The transmittance spectra indicate the four characteristic absorption maxima at the wavelengths of 680, 685, 729 and 744 nm, which were not observed for the undoped CdS film. Band gap energy Eg decreases from 2.43 to 2.37 eV with increasing Co content from x=0 to 0.10. The Co-doped Cd1−xCoxS films grown by spray pyrolysis (Type 1) didnot show any sign of ferromagnetic behavior. However, the Co diffused CdS films (Type 2) have clear ferromagnetic loops.

The influence of substrate temperature on the morphology, optical and electrical properties of thermal-evaporated ZnSe thin films

Abstract: The structural, morphological, optical and electrical properties of ZnTe films deposited by evaporation were investigated as a function of substrate temperature (at −123 and 27 °C) and post-deposition annealing temperature (at 200, 300 and 400 °C). It was determined that films deposited at both substrate temperatures were polycrystalline in nature with zinc-blende structure and a strong (1 1 1) texture. A small Te peak was detected in XRD spectra for both substrate temperatures, indicating that as-deposited ZnTe films were slightly rich in Te. Larger grains and a tighter grain size distribution were obtained with increased substrate temperature. Scanning electron microscopy (SEM) studies showed that the microstructures of the as-deposited films agreed well with the expectations from structure zone model. Post-deposition annealing induced further grain growth and tightened the grain size distribution. Annealing at 400 °C resulted in randomization in the texture of films deposited at both substrate temperatures. Optical spectroscopy results of the films indicated that the optical band gap value increased from 2.13 to 2.16 eV with increased substrate temperature. Increasing the annealing temperature sharpened the band-edge. Resistivity measurements showed that the resistivity of films deposited at substrate temperatures of −123 and 27 °C were 32 Ω cm, and 1.0 × 104 Ω cm, respectively with corresponding carrier concentrations of 8.9 × 1015 cm−3 and 1.5 × 1014 cm−3. Annealing caused opposite changes in the film resistivity between the samples prepared at substrate temperatures of −123 and 27 °C.

Zinc Oxide-From Synthesis to Application: A Review.

Abstract: Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, sol-gel method, solvothermal and hydrothermal method, method using emulsion and microemulsion enviroment and other methods of obtaining zinc oxide were classified as chemical methods. In the next part of this review, the modification methods of ZnO were characterized. The modification with organic (carboxylic acid, silanes) and inroganic (metal oxides) compounds, and polymer matrices were mainly described. Finally, we present possible applications in various branches of industry: rubber, pharmaceutical, cosmetics, textile, electronic and electrotechnology, photocatalysis were introduced. This review provides useful information for specialist dealings with zinc oxide.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Abstract: Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6–20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS–CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Thin Film Deposition Methods for CuInSe2Solar Cells

Abstract: CuInSe2 and its alloys with Ga and/or S are among the most promising absorber materials for thin film solar cells. CuInSe2-based solar cells have shown long-term stability and the highest conversion efficiencies of all thin film solar cells, above 19%. Solar cells based on these materials are also very stable, thus allowing long operational lifetimes. The preparation of a thin film solar cell is a multistage process where every step affects the resulting cell performance and the production cost. CuInSe2 and other Cu chalcopyrites can be prepared by a variety of methods, ranging from physical vapor deposition methods such as evaporation and sputtering to low-temperature liquid phase methods such as electrodeposition. The present review discusses first the concept and operation principle of thin film solar cells, as well as the most important thin film solar cell materials. Next, the properties of CuInSe2 and related compounds, as well as features of solar cells made thereof are reviewed. The last ...

Wide Band Gap Chalcogenide Semiconductors.

Abstract: Wide band gap semiconductors are essential for today's electronic devices and energy applications because of their high optical transparency, controllable carrier concentration, and tunable electrical conductivity. The most intensively investigated wide band gap semiconductors are transparent conductive oxides (TCOs), such as tin-doped indium oxide (ITO) and amorphous In-Ga-Zn-O (IGZO), used in displays and solar cells, carbides (e.g., SiC) and nitrides (e.g., GaN) used in power electronics, and emerging halides (e.g., γ-CuI) and 2D electronic materials (e.g., graphene) used in various optoelectronic devices. Compared to these prominent materials families, chalcogen-based (Ch = S, Se, Te) wide band gap semiconductors are less heavily investigated but stand out because of their propensity for p-type doping, high mobilities, high valence band positions (i.e., low ionization potentials), and broad applications in electronic devices such as CdTe solar cells. This manuscript provides a review of wide band gap chalcogenide semiconductors. First, we outline general materials design parameters of high performing transparent semiconductors, as well as the theoretical and experimental underpinnings of the corresponding research methods. We proceed to summarize progress in wide band gap (EG > 2 eV) chalcogenide materials-namely, II-VI MCh binaries, CuMCh2 chalcopyrites, Cu3MCh4 sulvanites, mixed-anion layered CuMCh(O,F), and 2D materials-and discuss computational predictions of potential new candidates in this family, highlighting their optical and electrical properties. We finally review applications-for example, photovoltaic and photoelectrochemical solar cells, transistors, and light emitting diodes-that employ wide band gap chalcogenides as either an active or passive layer. By examining, categorizing, and discussing prospective directions in wide band gap chalcogenides, this Review aims to inspire continued research on this emerging class of transparent semiconductors and thereby enable future innovations for optoelectronic devices.