Zinc Oxide Semiconductor Thin Films Research Articles

Characterization of Zinc Oxide Semiconductor Thin Film Treated with Cold Plasma

In this study, the photovoltaic properties of zinc oxides are investigated. Different stoichiometries of zinc oxide can be made using vacuum deposition. Thermally evaporated zinc produces thin films of ZnO composed of orthorhombic and tetragonal phases that define the material's characteristics and performance. On-thermal plasma has removed a very thin layer from the surface of the thin film, known as non-thermal plasma, and made a surface cleanup. Measurements of the Atomic Force Microscope (AFM) show that the value of the granular volume rate increases when the duration of exposure to non-heat plasma increases. Measurements of the Atomic Force Microscope (AFM) show that there is an increase in thin film surface roughness values (Roughness, Sq), as well as the square root of the average roughness of the thin film surface (RMS), and this increase in roughness appears as the duration of exposure to non-thermal plasma increases.

On-Substrate Joule Effect Heating by Printed Micro-Heater for the Preparation of ZnO Semiconductor Thin Film.

Fabrication of printed electronic devices along with other parts such as supporting structures is a major problem in modern additive fabrication. Solution-based inkjet printing of metal oxide semiconductor usually requires a heat treatment step to facilitate the formation of target material. The employment of external furnace introduces additional complexity in the fabrication scheme, which is supposed to be simplified by the additive manufacturing process. This work presents the fabrication and utilization of micro-heater on the same thermal resistive substrate with the printed precursor pattern to facilitate the formation of zinc oxide (ZnO) semiconductor. The ultraviolet (UV) photodetector fabricated by the proposed scheme was successfully demonstrated. The performance characterization of the printed devices shows that increasing input heating power can effectively improve the electrical properties owing to a better formation of ZnO. The proposed approach using the on-substrate heating element could be useful for the additive manufacturing of functional material by eliminating the necessity of external heating equipment, and it allows in-situ annealing for the printed semiconductor. Hence, the integration of the printed electronic device with printing processes of other materials could be made possible.

Investigating Zinc Ketoiminates as a New Class of Precursors for Solution Deposition of ZnO Thin Films.

Zinc oxide (ZnO) has been recognized as one of the most promising metal oxide semiconductor material for processing low-cost thin film transistors (TFTs). Within the scope of this work, we demonstrate a simple, stabilizer free and very efficient chemical solution deposition (CSD) route to grow high quality ZnO layers. The identification of a highly soluble zinc ketoiminate precursor that undergoes hydrolysis under ambient conditions with the facile cleavage of the ligands was the key to develop a simple and straightforward process for ZnO thin films under mild process conditions. Upon heat treatment at moderate temperatures, the precursor decomposes cleanly yielding polycrystalline ZnO thin films, which was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composition was investigated employing complementary techniques such as X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) which revealed high purity ZnO layers. The functional properties in terms of transparency and optical band gap were determined by ultraviolet-visible (UV-Vis) spectroscopy. The transparent ZnO semiconductor thin films serve as active channel layer of thin film transistors (TFT) which was demonstrated by spin coating of the precursor. Subsequent curing in ambient air, yields a 10 nm film that is sufficient to fabricate working TFTs test structures.

Effect of Al doping on crystallography and electro-optical properties of ZnO semiconductor thin films prepared by electrospinning

Zinc oxide (ZnO) thin film has in recent years emerged due to its unique physical, electrical and chemical properties. The microstructural and optical properties of nanocrystallite ZnO films fabricated using electrospinning and post-calcination, undoped and doped with aluminum, (AZO nanostructure films) were investigated in this study. The results indicated that the crystallized and monolithic AZO films comprised perfectly linked ZnO nanoparticles (NPs). Al incorporation deformed the lattice geometry (a and c axis) and crystallite size of (002) plane, and led to formation of zinc vacancies and Al interstitial/substituted sites. Functional molecule groups and optical properties of pristine ZnO and AZO films were studied by far-FTIR, PL and UV–Vis techniques. Our findings showed that doping ZnO with Al resulted in the Zn-O bond shifting towards higher energy levels, and it polarized the visible lights more than pure ZnO thin films. Furthermore, the formation of the large concentration of point defects in sub-atomic structure of AZO (6 wt% Al) reduced the optical band gap energy of ZnO from the 3.4 e.V to 3.05 eV. The optical transmittance of AZO films was higher than 83% in visible light range. The electrical conductivity of ZnO film was improved by Al incorporation. The results of present work indicated that the electrospinning is a promising method to fabricate the nanostructured AZO films for use in electro-optical applications such as solar cells.

Thin film transistor performance of amorphous indium–zinc oxide semiconductor thin film prepared by ultraviolet photoassisted sol–gel processing

We have fabricated an amorphous indium–zinc oxide (IZO, In/Zn = 3/1) semiconductor thin-film transistor (AOS-TFT) by the sol–gel technique using ultraviolet (UV) photoirradiation and post-treatment in high-pressure O2 at 200 °C. The obtained TFT showed a hole carrier mobility of 0.02 cm2 V−1 s−1 and an on/off current ratio of 106. UV photoirradiation leads to the decomposition of the organic agents and hydroxide group in the IZO gel film. Furthermore, the post-treatment annealing at a high O2 pressure of more than 0.6 MPa leads to the filling of the oxygen vacancies in a poor metal–oxygen network in the IZO film.

Tunneling condition at high Schottky barrier and ambipolar transfer characteristics in zinc oxide semiconductor thin film transistor

This study investigates the behavior of SiOC as gate dielectric materials for zinc-based oxide semiconductor thin film transistors (TFTs). The SiOC with a high potential barrier due to a low ionic energy at a Poole–Frenkel (PF) contact was suitable for use as a gate dielectric material to support tunneling in ZnO/SiOC TFTs. The performance of the ZnO TFTs for the low-polarization SiOC improved by introducing a direct tunneling phenomenon in the minority carriers of the SiOC depletion layer due to the decrease in the activation energy and the very high Schottky barrier (SB) of the SiOC material. PF emission was achieved at a non-polar SiOC with a high SB, and the mobility-stability of the TFTs with the PF contact dramatically improved. The TFT of the PF contact with a high SB was free from a shift in the threshold voltage with a decrease of the drain voltage.

Interrelation between Chemical, Electronic, and Charge Transport Properties of Solution-Processed Indium–Zinc Oxide Semiconductor Thin Films

Solution-processed metal oxide semiconductors are of high interest for the preparation of high-mobility transparent metal oxide (TMO) semiconductor thin films and thin film transistors (TFTs). It has been shown that the charge transport properties of indium–zinc oxide (IZO) thin films from molecular precursor solutions depend strongly on the preparation conditions, in particular on the precursor conversion temperature Tpc and, to some surprise, also on the concentration of the precursor solution. Therefore, the chemical and the electronic structure of solution-processed IZO thin films have been studied in detail with X-ray photoelectron spectroscopy (XPS) under systematic variation of Tpc and the concentration of the precursor solution. A distinct spectral feature is observed in the valence band spectra close to the Fermi level at EB = 0.45 eV binding energy which correlates with the trends in the sheet resistivity, the field effect mobility μFE, and the optical gap Egopt from four-point-probe (4PP), TFT, and UV–vis measurements, respectively. A comprehensive model of the interrelation between the conditions during solution-processing, the chemical and electronic structure, and the charge transport properties is developed.

Characterization of low-temperature solution-processed indium–zinc oxide semiconductor thin films by KrF excimer laser annealing

We have employed KrF excimer laser annealing (ELA) treatment on sol–gel derived indium–zinc oxide (IZO) precursor films to develop a method of low thermal-budget processing. As-coated IZO sol–gel film was dried at 150°C and then annealed using KrF excimer laser irradiation under ambient air. The laser irradiation energy density was adjusted to 150, 250, 350, and 450mJ/cm2 to investigate the effects of laser irradiation energy density on the microstructure, surface morphology, optical transmittance, and electrical properties of laser annealed IZO thin films. Results of GIXRD and TEM-SAED indicated that the ELA IZO thin films had an amorphous phase structure. The surface characteristics and electrical properties of laser annealed IZO thin films were significantly affected by the laser irradiation energy density. It was found that the dried IZO sol–gel films irradiated with a laser energy density of 350mJ/cm2 exhibited the flattest surface, the highest average optical transmittance in the visible region, and the best electrical properties among all ELA samples.

Sol–gel derived undoped and boron-doped ZnO semiconductor thin films: Preparation and characterization

We report the influence of boron doping concentration on the microstructure, electrical and optical properties of solution-processed zinc oxide (ZnO) thin films. The B doping concentration in the resultant solutions was varied from 0 to 5 at%, and the pH value of each synthetic solution was adjusted to 7.0. XRD measurements, SEM observations, and SPM examinations revealed that boron doping produced ZnO thin films consisting of a fine grain structure with a flat surface morphology. Moreover, ZnO thin films doped with B raised the texture coefficient along the (002) plane. All B-doped ZnO (ZnO:B) thin films exhibited higher transparency than that of the undoped ZnO thin film in the wavelengths between 350 and 650 nm. The optical band gap and Urbach energy of the ZnO:B thin films were higher than those of the undoped thin film. According to electrical transport characteristics, the 1% B-doped ZnO thin film exhibited the highest Hall mobility of 17.9 cm2/V s, the highest electron concentration of 1.2×1015 cm−3, and the lowest electrical resistivity of 2.2×102 Ω cm among all of the ZnO:B thin films.

Mid-infrared surface plasmon resonance in zinc oxide semiconductor thin films

Surface plasmon resonance (SPR) in semiconducting materials at mid-infrared (mid-IR) energies offers the potential for new plasmonic functionalities and integration schemes. Mainstream semiconductors are transparent to mid-IR energies, thus a tightly integrated monolithic package for SPR sensing becomes feasible. We report mid-IR surface plasmon resonance in zinc oxide as a model material for semiconductors with 4 × 1019 to 8 × 1019 cm−3 carriers. The surface plasmon modes were characterized using spectroscopic IR-ellipsometry and compared to a reflectivity simulation. The data confirm the feasibility of mid-IR SPR, show a generic ability for plasmon tuning, and demonstrate the predictive power of the reflectivity model.

Photosensitivity n-channel ZnO phototransistor for optoelectronic applications: Modeling of ZnO TFT

The zinc oxide semiconductor thin film transistor was fabricated on a SiO 2/Si substrate by sol gel method. The ZnO film is consisted of nanofibers with the changing diameter along the fibers. Electrical characteristics of the zinc oxide transistor under dark and white light illuminations were analyzed. The mobility value of the ZnO TFT was found to be 1.86 × 10 −2 cm 2/V s. The ZnO thin film transistor works in an n-channel operational mode because the drain current increases with the positive gate voltages. A significant increase in the drain current of ZnO TFT is observed with a maximum photosensitivity of 100 under visible light illumination. It is concluded that the ZnO thin film transistor can be used in visible photo-detecting device applications.

The Effect of Operational Parameters on the Photocatalytic Degradation of C.I. Reactive Yellow 86 Textile Dye Using Manganese Zinc Oxide Nanocomposite Thin Films

AbstractManganese zinc oxide semiconductor thin films have been deposited by sol-gel process on glass substrate which was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and UV-Vis spectroscopy (UV-Vis). The as deposited thin films on glass are monophasic with good crystallinity and hexagonal wurtzite structure. In order to increase the photocatalytic efficiency of the zinc oxide coatings the authors optimized the sol-gel process and doped the coatings with manganese. By slightly doping the zinc oxide films with 2 at% manganese the photocatalytic performance is increased compared to pure zinc oxide semiconductor thin films. The photocatalytic performance of the manganese zinc oxide films was evaluated by the decomposition of a textile dye (C.I. Reactive Yellow 86) (RY86) with UV light irradiation. This investigation will give a new insight to understanding the industrial textile dye photodegradation in aquatic environment.

Indium zinc oxide semiconductor thin films deposited by dc magnetron sputtering at room temperature

Amorphous indium zinc oxide (IZO) thin films were prepared on glass substrates by dc magnetron sputtering at room temperature. The resistivity of IZO films could be controlled between 3.8 × 10 −3 and 2.5 × 10 6 Ω cm by varying the oxygen partial pressure during deposition, while keep the average transmittance over 83%. With IZO films as channel layers, whose surface root-mean-square roughness was less than 1 nm, thin film transistors were fabricated at room temperature, showing enhanced mode operation with good saturation characteristics, mobility of 5.2 cm 2 V −1 s −1, threshold voltage of 0.94 V and on/off ratio of ∼10 4.

Step-Flow Homoepitaxial Growth of Zinc Oxide Semiconductor Thin Films with A Vapor-Growth Method

As a safe, simple, and low energy-consumption growth method of oxide semiconductors, we have developed a mist-chemical vapor deposition (CVD) technique. This technique has been applied to homoepitaxial growth of zinc oxide (ZnO) semiconductor thin films on ZnO bulk substrates. Step-flow growth has been achieved at the growth temperatures of 950∼1000°C. The step height was 0.26nm, that is, one molecular-layer height, in the initial growth stage (20∼50nm in ZnO epilayer thickness) and it is enhanced as 0.52nm, that is, two molecular-layers height, for the thicker (>200nm) films, due to coalescence of two terrace layers. Terrace shapes have been well interpreted in terms of the balance between incorporation and evaporation of adatoms at the terrace edges. The homoepitaxial ZnO layers exhibited good crystallinity comparable to that of substrates, but the inclusion of impurities, probably from the source materials due to their insufficient purity as semiconductor sources, remained as one of the most important problems to be overcome for future evolution of this unique growth technique.

Effect of Molarity of Precursor Solution on Nanocrystalline Zinc Oxide Thin Films

During the last two decades, the use of transparent conducting films of non-stoichiometric and doped metallic oxides for the conversion of solar energy into electrical energy has assumed great significance. A variety of materials, using various deposition techniques, has been tried for this purpose [1-3]. Among these various materials, zinc oxide (ZnO) is one of the prominent oxide semiconductors suitable for photovoltaic applications because of its high electrical conductivity and optical transmittance in the visible region of the solar spectrum [4]. Furthermore, thin films of ZnO have shown good chemical stability against hydrogen plasma, which is of prime importance in a-Si:H-based solar-cell fabrication. Thus, zinc oxide can serve as a good candidate for replacing SnO2 and indium tin oxide (ITO) films in Si:H-based solar cells. One of the outstanding features of ZnO is its large excitonic binding energy, i.e. 60meV, leading to the existence of excitons at room temperature and even at higher temperatures [5-8]. These unique characteristics have generated a wide range of applications of ZnO. For example, gas sensors [9], surface acoustic devices [10], transparent electrodes and solar cells. Many techniques are used for preparing the transparent conducting ZnO films, such as RF sputtering [11], evaporation [12], chemical vapour deposition [13], ion beam sputtering [14] and spray pyrolysis [15–18]. Among these, the spray pyrolysis technique has attracted considerable attention due to its simplicity and large-scale production combined with low-cost fabrication. By using this technique, one can produce large-area coatings without any need for ultra-high vacuum. Thus, the capital cost and the production cost of high-quality zinc oxide semiconductor thin films are lowest among all other techniques. In the present work, we have synthesized ZnO films by using the spray pyrolysis technique. A number of films have been prepared by changing the molarity of the precursor solution. The prepared films have been characterized with regard to their structural, morphological and electrical properties.

Hydrogenated aluminium-doped zinc oxide semiconductor thin films for polymeric light-emitting diodes

Highly conducting transparent thin films of aluminium(Al)-doped zinc oxide (ZnO:Al) were deposited by a radio frequency magnetron-sputtering technique using an argon and hydrogen gas mixture at room temperature. Hydrogen serves as a shallow donor and plays a critical role in improving the Al doping efficiency to enhance the conductivity of thin films. The effect of hydrogen partial pressure on the properties of ZnO:Al films was investigated in detail. Polycrystalline ZnO:Al films with a surface roughness of about 2 nm, conductivity of 1.97 × 103 S cm−1, transmittance of over 83% in the visible wavelength region and an optical band gap of 3.93 eV were achieved at a hydrogen partial pressure of 7.5 × 10−4 Pa. A ZnO:Al film with the desired properties was used as an anode contact in a bi-layer polymeric light-emitting diode. A polyethylene dioxythiophene–polystyrene sulfonate doped with poly(styrenesulfonic acid) (PEDOT: PSS) and phenyl-substituted poly(p-phenylene vinylene) (Ph-PPV) were employed as a hole transport layer and a light-emitting layer, respectively. The electro-luminescence performance of the aforementioned diode was studied and compared to a control device with an indium tin oxide anode.