Low-temperature Au-induced crystallization of hydrogenated amorphous Si0.5Ge0.5 thin films using Au solution

Low-temperature (∼400 °C) metal-induced crystallization of hydrogenated amorphous Si_0.5Ge_0.5 thin films using Au solution has been investigated by X-ray diffraction, Raman spectra, scanning electron microscopy and atomic force microscopy. It was shown that Au solution significantly promotes the crystallization of the films at low temperatures. The effects of annealing temperature and concentration of the Au solution on the structure and morphology of the films were analyzed. The increase in crystallinity was observed with increasing the annealing temperature. The Raman shifts of Ge–Ge and Si–Ge peaks with the annealing temperature were also discussed.     

Role of thermal annealing on SiGe thin films fabricated by PECVD

Amorphous Silicon Germanium (a-SiGe) thin films of 500 nm thickness are deposited on silicon substrates using Plasma Enhanced Chemical Vapour Deposition (PECVD). To obtain polycrystalline nature of films, thermal annealing is done at various temperature (450–600 °C) and time (1–10 h). The surface morphology of the pre- and post-annealed films is investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The crystallographic structure of the film is obtained by X-ray diffraction method. Raman spectroscopy is carried out to quantify the Ge concentration and the degree of strain relaxation in the film. Nano-indentation is performed to obtain the mechanical properties of the film. It is found that annealing reduces the surface roughness of the film and increases the Ge concentration in the film. The grain size of the film increases with increase in annealing temperature. The grain size is found to decrease with increase in annealing time up to 5 h and then increased. The results show that 550 °C for 5 h is the critical annealing condition for variation of structural and mechanical properties of the film. Recrystallization starts at this condition and results in finer grains. An increase in hardness value of 7–8 GPa has been observed. Grain growth occurs above this critical annealing condition and degrades the mechanical properties of the film. The strain in the film is only relaxed to about 55% even for 10 h of annealing at 600 °C. Transmission Electron Microscopy (TEM) observations show that the strain relaxation occurs by forming misfit dislocations and these dislocations are confined to the SiGe/Si interface.     

Effect of annealing temperature on optical and electrical properties of lead sulfide thin films

Lead sulfide (PbS) thin films with 150 nm thickness were prepared onto ultra-clean quartz substrate by the RF-sputtering deposition method. Deposited thin films of PbS were annealed at different temperatures 100 °C, 150 °C, 200 °C, 250 °C and 300 °C. X-ray diffraction pattern of thin films revealed that thin films crystallized at 150 °C. Crystalline thin films had cubic phase and rock salt structure. The average crystallite size of crystalline thin films was 22 nm, 28 nm and 29 nm for 150 °C, 200 °C and 250 °C respectively. From 150 °C to 250 °C increase in annealing temperature leads to increase in crystallite arrangement. FESEM images of thin films revealed that crystallite arrangement improved by increasing annealing temperature up to 250 °C. Increase in DC electrical conductivity by increasing temperature confirmed the semiconductor nature of crystalline thin films. Increase in dark current by increasing annealing temperature showed the effect of crystallite arrangement on carrier transport. Photosensitivity decreased by increasing annealing temperature for crystalline thin films that it was explained at the base of thermal quenching of photoconductivity and adsorption of oxygen at the surface of thin films that leads to the formation of PbO at higher temperatures.     

Effect of Ag photo-doping on structural,optical and phase change properties of GeTe chalcogenide films

This paper reports the effect of Ag photo-doping on optical, electrical and structural properties of GeTe:Ag thin films. The absence of sharp diffraction peak confirms the amorphous nature of as-deposited and photo-doped films. The decrease in reflectance of GeTe:Ag bilayer films with photo-doping reaction time has been observed. The RAMAN spectrum showed the characteristic Raman bands for GeTe₄ (127 cm⁻¹), long chain interactions of Te–Te chains (145 cm⁻¹) and a broad peak for Ge–Ge vibrations (275 cm⁻¹) without appreciable change in their position/shape with photodoped Ag concentration. The electrical resistivity measurement shows that photo-doping of Ag led to sharp amorphous-crystalline phase transition along with an increase in transition temperature and resistivity value in both amorphous as well as crystalline state. The annealing of photo-doped GeTe:Ag samples showed an enhancement in the crystallinity of GeTe phase without any segregation of Ag phases in annealed samples. The preferential formation of GeTe (200) phase upon crystallization has been observed for GeTe:Ag films. Different optical parameters have been calculated for photo-doped and annealed samples and are discussed in conjunction with the modification of network structure of GeTe with inclusion of photo-doped Ag content.     

Epitaxial growth of Ge thin film on Si (001) by DC magnetron sputtering

We have demonstrated that sub-10 nm-thick heteroepitaxial Ge films on Si (001) having smooth surfaces can be obtained by DC magnetron sputtering. Ge films grown at 350 °C preserve the smooth surfaces with a roughness root mean square (RMS) of 0.39 nm, whereas, the Ge films grown at 500 °C show significant roughness with an island-like morphology. In samples grown at 350 °C, it is confirmed that the Ge films are grown epitaxially by cross-section transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements. Rapid thermal annealing (RTA) at 720 °C is effective in improving the crystalline quality and the degradation in the roughness is negligible. Raman spectra and an XRD reciprocal space map reveal that the epitaxial Ge grown at 350 °C show an in-plane compressive strain and that the strain continues to remain after a 720 °C RTA.     

Ge-rich SiGe thin film deposition by co-sputtering in in-situ and ex-situ solid phase crystallization for photovoltaic applications

This study investigates the properties of high Ge content silicon-germanium thin films in the non-hydrogenated state (Ge-rich SiGe) deposited on glass by RF magnetron co-sputtering in both in-situ and ex-situ solid phase crystallization (SPC) at various temperatures, such as RT to 550 °C. The structural and optical characteristics of SiGe films have been explored systematically by optimizing growth temperature. Atomic composition of films was determined by EDX, which showed up to 77 at% of Ge. Structural properties were characterized by XRD, which revealed all samples to be in amorphous nature. The results from Raman and UV–VIS–IR transmittance measurements showed that the properties of amorphous Si_0.23Ge_0.77 films improved at 450 °C in both in-situ and ex-situ SPC processes. In addition, EDX exposed an advantage of in-situ process over ex-situ due to the incorporation of oxygen during ex-situ thermal annealing. Possible deposition at low substrate temperature as found here suggests that these Si_0.23Ge_0.77 films have a substantial potential to be used in thin film Si-based solar cells.     

Effect of annealing on the structural and optical properties of laser ablated nanostructured barium tungstate thin films

High quality BaWO₄ thin films are successfully deposited on quartz substrate for a duration of 30 min using pulsed laser ablation technique and using a laser radiation of wavelength 355 nm and the effect of thermal annealing on the structural and optical properties is studied by using techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, micro-Raman, FTIR and UV–visible spectroscopy. All the films show monoclinic crystalline structure with (2 0 2) plane as the preferred orientation of crystal growth. From the XRD analysis it is found that the optimum annealing temperature for better crystallization of the BaWO₄ film is 700 °C and there is no phase change observed with annealing temperature. The presence of the characteristic bands for the BaWO₄ in the Raman spectra of the films suggests the formation of BaWO₄ crystalline phase in all the films. SEM and AFM analyses show that as the annealing temperature increases the connectivity between individual grains increases and shows an ordered packing. The geometrical optimization and energy calculation of the title compound were done using the Gaussian 09 software package and the calculations were carried out using the CAM-B3LYP functional combined with standard Lanl2Dz basis set. The thickness of the films was calculated using lateral SEM images and also from optical transmission spectral data using PUMA software.     

Effect of annealing temperature on structural,electrical and optical properties of spray pyrolytic nanocrystalline CdO thin films

Nanocrystalline CdO thin films were prepared onto a glass substrate at substrate temperature of 300 °C by a spray pyrolysis technique. Grown films were annealed at 250, 350, 450 and 550 °C for 2.5 h and studied by the X-ray diffraction, Hall voltage measurement, UV-spectroscopy, and scanning electron microscope. The X-ray diffraction study confirms the cubic structure of as-deposited and annealed films. The grain size increases whereas the dislocation density decreases with increasing annealing temperature. The Hall measurement confirms that CdO is an n-type semiconductor. The carrier density and mobility increase with increasing annealing temperature up to 450 °C. The temperature dependent dc resistivity of as-deposited film shows metallic behavior from room temperature to 370 K after which it is semiconducting in nature. The metallic behavior completely washed out by annealing the samples at different temperatures. Optical transmittance and band gap energy of the films are found to decrease with increasing annealing temperature and the highest transmittance is found in near infrared region. The refractive index and optical conductivity of the CdO thin films enhanced by annealing. Scanning electron microscopy confirms formation of nano-structured CdO thin films with clear grain boundary.     

Microstructure evolution of amorphous silicon thin films upon annealing studied by positron annihilation

Amorphous silicon (a-Si) thin films were prepared on glass substrates by plasma enhanced chemical vapor deposition (PECVD). Influence of annealing temperature on the microstructure, surface morphology, and defects evolution of the films were studied by X-ray diffraction (XRD), atomic force microscope (AFM) and positron annihilation Doppler broadening spectroscopy (DBS) based on a slow positron beam, respectively. The S parameter of the as-deposited a-Si thin film is high, indicative of amorphous state of Si film with many defects. The a-Si gradually grows into polycrystalline silicon with increasing temperature to 650 °C. For the films annealed below ~450 °C, positron diffusion lengths are rather small because most positrons are trapped in the defects of the a-Si films and annihilated there. With further rising the temperature to 600 °C, the diffusion length of positrons increases significantly due to the removal of vacancy-type defects upon annealing at a high temperature. The results indicate that the coalescence of small vacancy-type defects in a-Si thin film and the crystallization of a-Si occur around 450 °C and 650 °C, respectively.     

Effect of thermal annealing on physical properties of vacuum evaporated In2S3 buffer layer for eco-friendly photovoltaic applications

The present communication reports the effect of thermal annealing on the physical properties of In₂S₃ thin films for eco-friendly buffer layer photovoltaic applications. The thin films of thickness 150 nm were deposited on glass and indium tin oxide (ITO) coated glass substrates employing thermal vacuum evaporation technique followed by post-deposition thermal annealing in air atmosphere within a low temperature range 150–450 °C. These as-deposited and annealed films were subjected to the X-ray diffraction (XRD), UV–vis spectrophotometer, current–voltage tests and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of as-deposited film is also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the as-deposited and annealed films (≤300 °C) have amorphous nature while films annealed at 450 °C show tetragonal phase of β-In₂S₃ with preferred orientation (109) and polycrystalline in nature. The crystallographic parameters like lattice constant, inter-planner spacing, grain size, internal strain, dislocation density and number of crystallites per unit area are calculated for thermally annealed (450 °C) thin films. The optical band gap was found in the range 2.84–3.04 eV and observed to increase with annealing temperature. The current–voltage characteristics show that the as-deposited and annealed films exhibit linear ohmic behavior. The SEM studies show that the as-deposited and annealed films are uniform, homogeneous and free from crystal defects and voids. The grains in the thin films are similar in size and densely packed and observed to increase with thermal annealing. The experimental results reveal that the thermal annealing play significant role in the structural, optical, electrical and morphological properties of deposited In₂S₃ thin films and may be used as cadmium-free eco-friendly buffer layer for thin films solar cells applications.     

Variation of the structural,optical and electrical properties of CBD CdO with processing temperature

Nanostructures of CdO thin films are prepared by chemical bath deposition (CBD) technique. The synthesized film is annealed in static air by using the hotplate at 373, 473, 573 and 673 K for 10 min. The effect of annealing temperature on structural, morphological, optical and electrical properties of CdO thin films has been investigated. The prepared thin films are characterised by X-ray diffraction (XRD), atomic force microscope (AFM), optical reflection microscope (ORM), UV–Visible Spectrophotometer and electrical resistivity. XRD shows the emergence of the cubic phase of CdO film in a preferred orientation (111) plane at 573 K. The AFM and ORM show that CdO films have smooth homogeneous surface in the formula with the emergence of nanoclusters gathering as nanoparticles with the average of grain size about 100 nm at 573 K. The optical properties prove that deposited films have high transparency within the visible range of the spectrum that reaches to more than 85% with a wide band gap that extends from 2.42 eV to 2.7 eV. The electrical properties of the CdO films show that resistivity decreases with increased annealing temperatures. In addition, it is proved that more than one activation energy appears and they change according to the temperature of annealing and this comes as a result of the polycrystalline structure. This study indicates that the properties of CdO thin films could be improved with annealing temperature and these films can be used in many technological applications.     

Structural and optoelectronic properties of nanostructured TiO2 thin films with annealing

About 480 nm thick titanium oxide (TiO₂) thin films have been deposited by electron beam evaporation followed by annealing in air at 300–600 °C with a step of 100 °C for a period of 2 h. Optical, electrical and structural properties are studied as a function of annealing temperature. All the films are crystalline (having tetragonal anatase structure) with small amount of amorphous phase. Crystallinity of the films improves with annealing at elevated temperatures. XRD and FESEM results suggest that the films are composed of nanoparticles of 25–35 nm. Raman analysis and optical measurements suggest quantum confinement effects since Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk TiO₂ Optical band gap energy of the as-deposited TiO₂ film is 3.24 eV, which decreases to about 3.09 eV after annealing at 600 °C. Refractive index of the as-deposited TiO₂ film is 2.26, which increases to about 2.32 after annealing at 600 °C. However the films annealed at 500 °C present peculiar behavior as their band gap increases to the highest value of 3.27 eV whereas refractive index, RMS roughness and dc-resistance illustrate a drop as compared to all other films. Illumination to sunlight decreases the dc-resistance of the as-deposited and annealed films as compared to dark measurements possibly due to charge carrier enhancement by photon absorption.     

Insight into the charge transport and degradation mechanisms in organic transistors operating at elevated temperatures in air

Operational stability of organic devices at above-room-temperatures in ambient environment is of imminent practical importance. In this report, we have investigated the charge transport and degradation mechanisms in pentacene based organic field effect transistors (OFETs) operating in the temperatures ranging from 25 °C to 150 °C under ambient conditions. The thin film characterizations techniques (X-ray photoelectron spectroscopy, X-ray diffraction and atomic force microscopy) were used to establish the structural and chemical stability of pentacene thin films at temperatures up to 150 °C in ambient conditions. The electrical behavior of OFETs varies differently in different temperature bracket. Mobility, at temperatures below 110 °C, is found to be thermally activated in presence of traps and temperature independent in absence of traps. At temperatures above 110 °C mobility degrades due to polymorphism in pentacene or interfacial properties. The degradation of mobility is compensated with the decrease in threshold voltage at high temperatures and OFETs are operational at temperatures as high as 190 °C. 70 °C has been identified as the optimum temperature of operation for our OFETs where both device behavior and material properties are stable enough to ensure sustainable performance.     

Raman spectroscopic study of In2S3 films prepared by spray pyrolysis

Indium sulfide (In₂S₃) thin films are of interest as buffer layers in chalcopyrite absorber based solar cells; and as media providing two-photon absorption for intermediate-band solar cells. We investigated the suitability of chemical spray pyrolysis (CSP) for growing In₂S₃ thin films in a structural order where indium atoms are preferentially in the octahedral sites. We sprayed aqueous or alcoholic solutions of indium chloride (InCl₃) and thiourea (SC(NH₂)₂) precursors onto a substrate with surface temperatures (T_S) of 205, 230, 275 and 320 °C. The as-deposited films grown from aqueous solutions were annealed in 5% H₂S containing atmosphere at 500 °C. We used Raman spectroscopy, X-ray diffraction and Energy Dispersive X-ray spectroscopy to evaluate the effect of growth temperature and the effect of annealing on the film structure and stoichiometry. The use of alcoholic solvent instead of aqueous allows us to use much lower T_S while preserving the quality of the β-In₂S₃ films obtained. Similarly, films with increased stoichiometry and quality are present at a higher T_S; and when annealed. The annealing of the films grown at T_S of 205 °C results in a much higher gain of the crystal quality compared to the gain when annealing the films grown at T_S of 320 °C, although the quality remain higher when deposited at T_S of 320 °C. Simultaneously with the increase of the film quality, there is a sign of increased quality of the crystal ordering with indium in the octahedral sites. Such a crystal ordering favor the use of CSP deposited In₂S₃ films in the intermediate band solar cells.     

Behavior of chemically deposited PbS thin films subjected to two different routes of post deposition annealing

Lead sulfide (PbS) thin films were prepared on soda lime glass substrates at room temperature by Chemical Bath Deposition (CBD) technique. This paper reports a comparative study of characteristic properties of as-prepared PbS thin films after thermal treatment through two different routes. Studies were carried out for as-prepared as well as rapidly and gradually annealed samples at 100, 200 and 300 °C. The characterizations of the films were carried out using X-ray diffraction, scanning electron microscopy and optical measurement techniques. The structural studies confirmed the polycrystalline nature and the cubic structure of the films. As-deposited films partly transformed to Pb₂O₃ when gradually annealed to 300 °C. The presence of nano crystallites was revealed by structural and optical absorption measurements. The values of average crystallite size were found to be in the range 18–20 nm. The variation in the microstructure, thickness, grain size, micro strain and optical band gap on two types of annealing were compared and analyzed. Data showed that post deposition parameters and thermal treatment strongly influence the optical properties of PbS films. Optical band gap of the film gets modified remarkably on annealing. Direct band gap energy values for rapidly and gradually annealed samples varied in the range of 1.68–2.01 eV and 1.68–2.12 eV respectively. Thus we were succeeded in tailoring direct band gap energies by post deposition annealing method.     

Effect of the substrate temperature on the electrical and structural properties of spray-deposited SnO2:F thin films

SnO₂:F thin films were prepared by the spray pyrolysis (SP) technique at substrate temperature in the range 360–480 °C. The effect of varying the substrate temperature on the electrical and structural properties of the films was investigated by studying the I–V characteristics, the X-ray diffraction patterns (XRD), and the scanning electron microscope images (SEM). The I–V characteristics of the films were improved by increasing the substrate temperature, i.e. the resistivity of the films had decreased from 98 to 0.22 Ω cm. The X-ray diffraction patterns taken at 400 and 480 °C showed that the films are polycrystalline and two directions of crystal growth appeared in the difractogram of the film deposited at the lower substrate temperature, which correspond to the reflections from the (1 1 0) and (2 0 0) planes. With the increase in the substrate temperature a new direction of crystal growth appeared, which corresponds to the reflection from the (1 0 1) plane. Also the (1 1 0) and (2 0 0) lines were slightly grown at the higher substrate temperature, which means the crystal growth was enhanced and the grain size had increased. The SEM images confirmed these results and showed larger grains and more crystallization for the higher substrate temperature too.     

Optical and electrical measurement of FeSe2 thin films obtained at low temperature

FeSe₂ thin films were prepared at low temperature by thermal annealing at 350 °C during 6 h of sequentially evaporated iron and selenium films under selenium atmosphere. The structural, optical and electrical characteristics were investigated. The roughness of films (~76 nm) was confirmed by AFM images. Moreover, optical band gap of FeSe₂, which was evaluated as nearly 1.11 eV and confirmed by the electrical study which yielded a value in the order of 1.08 eV. The electrical conductivity, conduction mechanism, dielectric properties and relaxation model of theses thin films were studied using impedance spectroscopy technique in the frequency range 5 Hz–13 MHz under various temperatures (180–300 °C). Besides, complex impedance and AC conductivity have been investigated on the basis of frequency and temperature dependence.     

Preparation and characterization of TiO2 thin film by thermal oxidation of sputtered Ti film

Titanium dioxide (TiO₂) thin films were successfully prepared on quartz substrate by thermal oxidation of sputtered titanium film in air. The structure, composition, morphology and optical properties of oxidized TiO₂ films were characterized by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and UV-visible spectroscopy. Meanwhile, the photocatalytic activity of the films was evaluated on the basis of the degradation of methyl orange solution under UV irradiation. Ti films after oxidation present mainly in TiO₂ form with a larger amount of adsorbed O₂, and oxidation temperature has a strong impact on the crystal structure and properties of the films. A phase transformation of anatase to rutile for oxidized TiO₂ films occurred in the temperature range of 700–800 °C. The energy band gap of oxidized TiO₂ films decreased first and then increased with annealing temperature. Furthermore, TiO₂ film oxidized at 600 °C exhibited the best photocatalytic activity due to suitable crystal phase and size. These results might contribute to the synthesis of metal oxide thin films with expectant structural morphology and properties by thermal oxidation methods.     

Effect of annealing on structural,optical and electrical properties of pulse electrodeposited tin sulfide films

Polycrystalline tin sulfide (SnS) thin films were grown on conducting glass substrates by pulse electrodeposition. The effect of annealing on the physical properties such as structure, morphology, optical, and opto-electronic properties were evaluated to understand the effect of post-deposition treatment for SnS films. Annealing at temperatures higher than 250 °°C resulted in the formation of SnS₂ as a second phase, however, no significant grain growth or morphological changes were observed for films after annealing at 350 °C. A small change in band gap of 0.1 eV observed for films annealed at 350 °C was interpreted as due to the formation of SnS₂ rather than due to morphological changes. This interpretation was supported by X-ray diffractometry, scanning electron microscopy, and Raman spectral data. The electric conduction in the films is controlled by three shallow trap levels with activation energies 0.1, 0.05, and 0.03 eV. The trap with energy 0.03 eV disappeared after annealing at higher temperature, however, the other two traps were unaffected by annealing.     

Investigation of optical and electronic properties in Al–Sn co-doped ZnO thin films

Al-Sn co-doped ZnO thin films were deposited onto quartz substrates by sol-gel processing. The surface morphology and electrical and optical properties were investigated at different annealing temperatures. The surface morphology showed a closely packed arrangement of crystallites in all the doped films. As prepared co-doped films show a preferred orientation along an (0 0 2) plane. This preferred orientation was enhanced by increasing the annealing temperature to between 400 °C and 500 °C, but there was a shift to the (1 0 1) plane when the annealing temperature rose above 500 °C. These samples show, on average, 91.2% optical transmittance in the visible range. In this study, the optical band gap of all the doped films was broadened compared with pure ZnO, regardless of the different annealing temperature. The carrier concentration and carrier mobility of the thin films were also investigated.