Preparation of nanocrystalline PbS thin films and effect of Sn doping and annealing on their structural and optical properties

Nanocrystalline PbS and Sn doped PbS thin films were successfully deposited on suitably cleaned glass substrate at constant room temperature, using the chemical bath deposition technique. Before, adding Sn doping content, the pure PbS thin films were deposited at room temperature for several dipping times to optimize the deposition time. After deposition, the films were also annealed at 400 °C for 1 h in air. The crystal structures of the films were determined by X-ray diffraction studies. The films were adherent to the substrate and well crystallized according to cubic structure with the preferential orientation (2 0 0). The crystallite size of the pure PbS thin films at optimized deposition time 30 min was found to be 40.4 nm, which increased with Sn content in pure PbS thin film. The surface roughness was measured by AFM studies. The band gaps of the films were determined by transmission spectra. Experiments showed that the growth parameters, doping and annealing, influenced the crystal structure, and optical properties of the films.     

New natively textured surface Al-doped ZnO-TCOs for thin film solar cells via magnetron sputtering

Natively textured surface aluminum doped zinc oxide (ZnO:Al) thin films were directly deposited via pulsed direct current (DC) reactive magnetron sputtering on glass substrates. During the reactive sputtering process, the oxygen gas flow rate was varied from 8.5 sccm to 11.0 sccm. The influences of oxygen flow rate on the structural, electrical and optical properties of naturally textured ZnO:Al TCO thin films with milky surface were investigated in detail. Gradual oxygen growth (GOG) technique was developed in the reactive sputtering process for textured ZnO:Al thin films. The light-scattering ability and optical transmittance of the natively textured ZnO:Al TCO thin films can be improved through gradual oxygen growth method while maintaining a low sheet resistance. Typical natively textured ZnO:Al TCO thin film with crater-like surface exhibits low sheet resistance (R_s ～ 4 Ω), high transmittance (T_a > 85%) in visible optical region and high haze value (12.1%).     

Epitaxial growth of non-polar m-plane ZnO thin films by pulsed laser deposition

Non-polar ZnO thin films were deposited on m-plane sapphire substrates by pulsed laser deposition at various temperatures from 300 to 700 °C. The effects of growth temperature on surface morphology, structural, electrical, and optical properties of the films were investigated. All the films exhibited unique m-plane orientation indicated by X-ray diffraction and transmission electron microscopy. Based on the scanning electron microscopy and atomic force microscopy, the obtained films had smooth and highly anisotropic surface, and the root mean square roughness was less than 10 nm above 500 °C. The maximum electron mobility was ～18 cm²/V s, with resistivity of ～0.26 Ω cm for the film grown at 700 °C. Room temperature photoluminescence of the m-plane films was also investigated.     

Performance evaluation of ZnO–CuO hetero junction solid state room temperature ethanol sensor

A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response (S = R_air/R_alcohol) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R² of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature.     

Growth of p-type ZnO thin films by using an atomic layer epitaxy technique and NH3 as a doping source

Nitrogen-doped, p-type ZnO thin films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C₂H₅)₂ [Diethylzinc, DEZn], H₂O and NH₃ as a zinc precursor, an oxidant and a doping source gas, respectively. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 210 Ω cm with a hole concentration of 3.41 × 10¹⁶ cm^− 3. Low temperature-photoluminescence analysis results support that the nitrogen ZnO after annealing is a p-type semiconductor. Also a model for change from n-type ZnO to p-type ZnO by annealing is proposed.     

Room temperature ferromagnetism in Co doped ZnO within an optimal doping level of 5%

We report on the structural, micro-structural and magnetic properties of Zn_1?xCo_xO (0 ≤ x ≤ 0.1) system. Electron probe micro-structural analysis on 5% Co doped ZnO indicates the presence of segregated cobalt oxide which is also confirmed from the Co 2p core level X-ray photoelectron spectrum. The presence of oxygen defects in lower percentage of Co doped ZnO (≤5%) enhances the carrier mediated exchange interaction and thereby enhancing the room-temperature ferromagnetic behaviour. Higher doping percentage of cobalt (>5%) creates weak link between the grains and suppresses the carrier mediated exchange interaction. This is the reason why room temperature ferromagnetism is not observed in 7% and 10% Co doped ZnO.     

Effects of the sulfidation temperature on the structure,composition and optical properties of ZnS films prepared by sulfurizing ZnO films

Nanocrystalline ZnS films have been prepared by sulfidation of the reactive magnetron sputtered ZnO films. The structure, composition and optical properties of the sulfurized ZnO films as a function of the sulfidation temperature (T_S) have been systematically studied. It is found that at T_S ⩾ 400 °C ZnO is completely converted to ZnS with the hexagonal structure. The ZnS films have a strongly (0 0 2) preferred orientation and an optical transparency of about 80% in the visible region. In addition, at T_S < 444.6 °C (boiling point of sulfur), some residual sulfur decomposed from H₂S gas can adhere to the sulfurized film surface while at T_S = 580 °C a S/Zn ratio much higher than the ideal stoichiometric proportion of ZnS is obtained for the ZnS films. ZnS films with a minimum XRD FWHM value of 0.165° and a good S/Zn ratio of 0.99 are obtained at a temperature of 500 °C indicating the ZnS films to be suitable for use in the thin film solar cells.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

Evolution of different structural phases of TiO2 films with oxygen partial pressure and Fe doping and their electrical properties

We have studied the influence of oxygen partial pressure (OPP; 250 mTorr–1 × 10^?5 Torr) and Fe doping (2 and 4 at.%) on structural and electrical properties of TiO₂ thin films on LaAlO₃ substrates. X-ray photoelectron spectroscopy suggests that Fe is not in metal cluster form. It is found that the evolution of the three phases; anatase, rutile and brookite of TiO₂ as well as the magneli phase (Ti_nO_2n?1) strongly depends on the OPP and Fe doping concentration. All the films grown at 250 mTorr show insulating behavior, whereas films grown at 1 × 10^?2 and 1 × 10^?4 Torr reveal high temperature metallic to low temperature semiconducting transition. Interestingly, films deposited at 1 × 10^?5 Torr reveal charge ordering, which is contributed to the magneli phase of TiO₂. The present study suggests that functionality of TiO₂ thin film based devices can be tuned by properly selecting the OPP and dopant concentration.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Structural and optical analyses of polycrystalline Zn1−xSbxSe thin films prepared by resistive heating technique

Here we report the influence of Sb doping on the structural and optical properties of Zn_1−xSb_xSe (0 ⩽ x ⩾ 0.15) thin films prepared by thermal evaporation technique on glass substrate. Various characterization techniques such as X-ray diffraction (XRD), EDS, Raman spectroscopy and spectroscopic ellipsometer are employed to assess the structural and optical properties of the deposited films. XRD analysis reveals the formation of polycrystalline cubic structure having preferred growth orientation along (1 1 1) plane without any evidence of secondary phases. Crystallographic parameters like grain size, micro strain, dislocation density, number of crystallites per unit area and texture coefficient point out the structural modification in ZnSe films with Sb inclusion. Raman analysis shows the existence of three 1LO, 2LO and 3LO phonon modes at 251, 511 and 745 cm⁻¹ in pure ZnSe while 3LO mode disappears by the incorporation of Sb atoms in ZnSe matrix. Increase in FWHM of Raman peaks with Sb concentration also indicates the change in crystalline quality of ZnSe films which is in accordance with our XRD results. Spectroscopic ellipsometry results demonstrate a decreasing trend for the optical band gap energy (from 2.61 eV to 1.81 eV) with increasing Sb content.     

Room temperature ferromagnetism in sputtered Zn1 − xCrxO thin films

Cr doped ZnO (Zn_1 ? xCr_xO) thin films with different Cr concentrations (0.4, 1.5, and 8.9 at.%) were deposited on Si substrates using RF magnetron sputtering. Film crystal structure was characterized using X-ray diffraction, and vibrating sample magnetometer measurements were used to investigate their magnetic properties. Unstable ZnO structure is present at low Cr concentrations, while secondary phases appear at higher Cr concentrations. 8.9 at.% Zn_1 ? xCr_xO film exhibits room temperature ferromagnetism and high 325 K Curie temperature, even after 300 °C annealing for 1 h. This result is promising and demonstrates Cr doped ZnO film's potential use in practical applications.     

Effect of bottom electrodes on dielectric relaxation and defect analysis of (Ba0.47Sr0.53)TiO3 thin film capacitors

The dielectric relaxation and defect analysis of (Ba_0.47Sr_0.53)TiO₃ (BST) thin films deposited on various bottom electrodes, such as Pt, Ir, IrO₂/Ir, Ru, RuO₂/Ru before and after annealing in O₂ ambient was investigated. Through the measurement of dielectric dispersion as a function of frequency (100 Hz ≤ f ≤ 10 MHz) and temperature (27°C ≤ T ≤ 150°C), we studied the trapping dielectric relaxation and defect quantity of the films, and proposed an equivalent circuit on the basis of the capacitance, admittance and impedance spectra. A shallow trap level located at 0.005–0.01 eV below the conduction band was observed from the admittance spectral studies in the temperature range of 27–150°C. The origin of dielectric relaxation and defect concentration was attributed to the existence of the grain boundary defect, interface defect and shallow trap level in the films. An equivalent circuit was established which can well explain the AC response and identify the contribution of defects on electrical properties of BST thin film. From the viewpoint of trapping phenomena and dielectric relaxation analyses, we propose Ir as the optimum material for bottom electrode to withstand the post-annealing treatment.     

Effects of substrate parameters on structure and optical properties of ZnO thin films fabricated by pulsed laser deposition

Highly oriented zinc oxide thin films have been grown on quartz, Si (1 1 1) and sapphire substrates by pulsed laser deposition (PLD). The effect of temperature and substrate parameter on structural and optical properties of ZnO thin films has been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectra and PL spectra. The experimental results show that the best crystalline thin films grown on different substrate with hexagonal wurtzite structure were achieved at growth temperature 400–500 °C. The growth temperature of ZnO thin film deposited on Si (1 1 1) substrate is lower than that of sapphire and quartz. The band gaps are increasing from 3.2 to 3.31 eV for ZnO thin film fabricated on quartz substrate at growth temperature from 100 to 600 °C. The crystalline quality and UV emission of ZnO thin film grown on sapphire substrate are significantly higher than those of other ZnO thin films grown on different substrates.     

Elastic properties of Ca5−xAxNb2TiO12 (A = Mg,Zn) microwave ceramics

Microwave dielectrics in Ca_5−xA_xNb₂TiO₁₂ (A = Mg, Zn) system have been prepared for different values of x by conventional solid-state ceramic route. The elastic properties of the ceramics were investigated as a function of composition by ultrasonic techniques. X-ray diffraction studies revealed that the ceramics form phase pure compounds for 0 ≤ x ≤ 1 and form mixture phases beyond x = 1. The elastic properties were strongly affected by structural transformations. Magnesium-based compositions have better elastic properties compared with zinc-based system.     

Formation of F-doped ZnO transparent conductive films by sputtering of ZnF2

Fluorine-doped ZnO transparent conductive thin films were successfully deposited on glass substrate by radio frequency magnetron sputtering of ZnF₂. The effects of rapid thermal annealing in vacuum on the optical and electrical properties of fluorine-doped ZnO thin films have been investigated. X-ray diffraction spectra indicate that no fluorine compounds, such as ZnF₂, except ZnO were observed. The specimen annealed at 500 °C has the lowest resistivity of 6.65 × 10^? 4 Ω cm, the highest carrier concentration of 1.95 × 10²¹ cm^? 3, and the highest energy band gap of 3.46 eV. The average transmittance in the visible region of the F-doped ZnO thin films as-deposited and annealed is over 90%.     

Tuning of charge carrier density of ZnO nanoparticle films by oxygen plasma treatment

In this work, the charge carrier density of ZnO nanoparticle films was modified after deposition and annealing by an oxygen plasma treatment. The respective films were utilized as active layers in thin film transistors. For a discussion of the plasma–surface interaction on the molecular level, the electrical behavior of the layers was investigated which in general is highly sensitive to low level variations in defect or doping densities. A treatment with remote oxygen plasma at 400 W for 10 s led to a shift of the turn-on voltage from ?12 to 4 V and a reduction of the off-current by more than two orders of magnitude. A model for the influence of oxygen species adsorbed to ZnO nanoparticle surfaces on electrical characteristics of ZnO nanoparticle thin film transistors is introduced.     

Deposition of nanocrystalline ZnO by wire explosion technique and characterization of the films' properties

ZnO films deposited on glass, quartz and Al on silicon mono-crystal Si (100) substrates by using the wire explosion technique were investigated by X-ray diffraction (XRD), UV–VIS spectroscopy, scanning electron (SEM) and atomic force microscopy (AFM) measurements. X-ray diffraction measurements have shown that ZnO films are mainly composed of (100), (002) and (101) orientation crystallites. The post-deposition thermal treatment at 600 °C temperature in air has shown that the composite of Zn/ZnO film was fully oxidized to ZnO film. The XRD spectra of the film deposited in oxygen atmosphere at room temperature present high intensity dominating peak at 2h = 36, 32° corresponding to the (101) ZnO diffraction peak. The small fraction of the film (7%) corresponds to the (002) peak intensity at 2h = 34, 42°. This result indicates the good crystal quality of the film and hexagonal wurtzite-type structure deposited by zinc wire explosion. The optical absorption spectra shows the bands at 374, 373 and 371 nm corresponding to deposition conditions. The SEM analysis shows that ZnO films presented different morphologies from fractal network to porous films depending on deposition conditions. AFM analysis revealed the grain size ranges from 50 nm to 500 nm. The nanoneedles up to 300 nm in length were found as typical structures in the film. It was demonstrated that the wire explosion technique is a feasible method to produce ZnO crystalline thin films and nanostructures.     

Effect of substrate temperature on the properties of pyrolytically deposited nitrogen-doped zinc oxide thin films

The effect of substrate temperature (T_s) on the properties of pyrolytically deposited nitrogen (N) doped zinc oxide (ZnO) thin films was investigated. The T_s was varied from 300 °C to 500 °C, with a step of 50 °C. The positive sign of Hall coefficient confirmed the p-type conductivity in the films deposited at 450 °C and 500 °C. X-ray diffraction studies confirmed the ZnO structure with a dominant peak from (1 0 0) crystal plane, irrespective of the variation in T_s. The presence of N in the ZnO structure was evidenced through X-ray photoelectron spectroscopy (XPS) analysis. The obtained high N concentration reveals that the 450 °C is the optimal T_s. Atomic force microscope (AFM) analysis showed that the surface roughness was increased with the increasing T_s until 400 °C but then decreased. It is found that the transmittance of the deposited films is increased with the increasing T_s. The optical band gap calculated from the absorption edge showed that the films deposited with T_s of 300 °C and 350 °C possess higher values than those deposited at higher T_s.     

Effect of Nd3+ incorporation on the microstructure and chemical structure of RF sputtered ZnO thin films

The present work aims at investigating the effects that different levels of Nd atoms incorporation can have on the microstructure and chemical structure of ZnO thin films. Undoped and Nd-doped ZnO films were deposited by RF co-sputtering from pure ZnO and metallic Nd targets in Ar plasma onto Si, quartz and glass substrates. The Nd concentration in the ZnO host matrix was varied in the range 0–26 at.% by varying the bias applied to the Nd target. A comprehensive characterization of the films properties was performed by X-ray photoelectron and Auger electron spectroscopies, X-ray fluorescence analysis, X-ray diffraction and scanning electron microscopy. At low Nd atomic concentration (Nd/Zn < 0.07) Nd atoms were successfully incorporated into the ZnO matrix, whose crystalline structure was preserved. A deterioration of the ZnO würtzite phase was observed on the contrary with increasing Nd content in the films together with the precipitation of a second phase, identified as Nd₂O₃.