The Effect of Substrate Temperature on the Optical Properties of MoO3 Nano-crystals Prepared Using Spray Pyrolysis

In this study, thin films of molybdenum oxide were prepared by spray pyrolysis technique on glass substrates. The influence of substrate temperature on their crystallographic structure, surface morphology, and optical properties was studied. The formation of a MoO₃ film on the substrate was confirmed through XRD analysis. Furthermore, the presence of the two phases α and β in each of the films was evident. The percentage of phase α varied from 55 % for the film deposited at 200 °C up to 97 % for the film deposited at 400 °C. According to SEM images, MoO₃ films have a sponge-type structure on the order of nanometers. Both the optical gap and the refraction index strongly depend on substrate temperature. The optical gap decreases from 3.63 eV for the film deposited at 150 °C up to 3.30 eV for the one prepared at 400 °C. On the contrary, the refraction index measured at 800 nm increases from 1.54 up to 1.61 for the films prepared at 150 °C and 400 °C, respectively.     

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.     

Microstructural and surface morphological studies on Co doped ZnS diluted magnetic semiconductor thin films

Microstructural and surface morphological studies of Co (2.5%) doped ZnS thin films deposited at different substrate temperatures (T_S) of 200, 400 and 600 °C by means of pulsed laser deposition are presented. The deposited films are in wurtzite-hexagonal crystal structure as confirmed by X-ray diffraction and Raman spectroscopy techniques. The films deposited at higher T_S show columnar morphology, as evidence by transmission electron microscopy measurements. Images of the surface topography have been taken by atomic force microscopy (AFM) for the film deposited at different T_S. The film deposited at T_S of 200 °C shows cone-like structures while deposited at T_S of 400 and 600 °C show columnar structures. A fractal analysis has been performed on AFM images to understand the microstructure and surface morphology of thin film at different T_S. Fractal analysis also reveals the morphological changes in the film with increasing T_S. The observed ferromagnetism is correlated with columnar growth of the film which can be used as diluted magnetic semiconductor for spintronic applications.     

Structural,morphological, optical and electrical properties of CdS thin films simultaneously doped with magnesium and chlorine

CdS thin films simultaneously doped with Mg and Cl at different doping concentrations (0, 2, 4, 6 and 8 at%) were prepared on glass substrates by spray pyrolysis technique using perfume atomizer at 400 °C. The effect of Mg and Cl doping concentration on the structural, morphological, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy, UV–Vis spectroscopy and dc electrical measurements, respectively. XRD analysis showed that the undoped and doped CdS films exhibit hexagonal structure with a preferential orientation along the (0 0 2) plane. The 2θ angle position of the (0 0 2) peak of the doped films was shifted towards a higher angle with increasing Mg and Cl concentration. The UV–Vis–NIR absorption spectra of Mg and Cl doped thin films are measured and classical Tauc approach was employed to estimate their band gap energies. The increase in band gap energy from 2.46 to 2.73 eV with the reduction in crystallite size supports quantum size effect. Raman spectra implied that more defects existed in the doped samples. Electrical studies showed that all the films have resistivity in the order of 10¹ Ω-cm and the CdS film with 6 at% Mg and Cl concentration has a minimum resistivity of 1.332 × 10¹ Ω-cm.     

Formation and properties of cadmium sulfide buffer layer for CIGS solar cells grown using hot plate bath deposition

In the present study, cadmium sulfide (CdS) thin films were deposited on different substrates [soda glass, fluoride doped tin oxide, and tin doped indium oxide (ITO) coated glass] by a hot plate method. To control the thickness and the reproducibility of the sample production, the thin films were coated at different temperatures and deposition times. The CdS thin films were heated at 400 °C in air and forming gas (FG) atmosphere to investigate the effect of the annealing temperatures. The thickness of the samples, measured by ellipsometry, could be controlled by the deposition time and temperature of the hot plate. The phase formation and structural properties of CdS thin films were studied by X-ray diffraction and scanning electron microscopy, whereas the optical properties were obtained by UV–vis spectroscopy. A hexagonal crystal structure was observed for CdS thin films and the crystallinity improved upon annealing. The structural and optical properties of CdS thin films were also enhanced by annealing at 400 °C in FG atmosphere (95 % N₂, 5 % H₂). The optical band gap was changed from 2.25 to 2.40 eV at different annealing temperatures and gas atmospheres. A higher electrical conductivity, for the sample annealed at FG, was noticed. The samples deposited on ITO and annealed in FG atmosphere showed the best structural and electrical properties compared to the other samples. CdS thin films can be widely used for application as a buffer layer for copper–indium–gallium–selenide solar cells.     

Structure, morphology and electrical characterizations of direct current sputtered ZnO thin films

ZnO thin films were deposited on glass substrates by direct current (DC) sputtering technique at room temperature (RT) to 400 °C with a 99.999% pure ZnO target. Then the samples deposited at RT were annealed in air from the RT to 400 °C. The effects of substrate temperature (T_s) and annealing treatment (T_a) on the crystallization behavior and the morphology have been studied by X-ray diffraction and atomic force microscopy. We also compared the structural properties of samples deposited at 400 °C on glass to those deposited on Pt/silicon substrate. The resistivity, surface roughness and size of the grains have also been studied and correlated to the thickness of ZnO films deposited on Pt/Si substrates. The experimental results reveal that the substrate has a major influence on the structural and morphological properties. For the films deposited on glass, below 400 °C, T_s and T_a have a similar influence on the structure of the films. Moreover, the ZnO samples deposited at RT and annealed in air have poor electrical properties.     

Effect of substrate temperature on the structural,morphological and optical properties of copper bismuth sulfide thin films deposited by electron beam evaporation method

Copper bismuth sulfide thin films were deposited at 200 °C, 300 °C, 400 °C and 500 °C on the glass substrates by electron beam evaporation method. X-ray diffraction study revealed that the copper bismuth sulfide films of single and mixed phases were formed as a function of substrate temperatures. Substrate temperature of 300 °C and 400 °C formed single phase Cu₄Bi₄S₉ and Cu₄Bi₅S₁₀ films respectively whereas substrate temperature of 500 °C formed mixed phases of Cu₄Bi₄S₉ and Cu₄Bi₅S₁₀ film. Crystallite size, dislocation density and microstrain of the films were modified by the various substrate temperatures. Surface morphology of the film Cu₄Bi₅S₁₀ deposited at 400 °C examined by scanning electron microscopy showed the distribution of spherical shaped particles on the film surface. The presence of copper, bismuth and sulfur elements in the deposited films was confirmed using energy dispersive spectral studies. The calculated direct optical band gap energy of the films deposited at different substrate temperature varied from 1.47 to 1.64 eV and the absorption coefficient is in the order of 10⁶ cm^?1.     

Structural, photoluminescence and optical properties of chemically deposited (Cd1−xBix)S thin films as a function of dopant concentration

In this study, (Cd_1?xBi_x)S thin films were successfully deposited on suitably cleaned glass substrate at 60 °C temperature, using the chemical bath deposition technique. After deposition, the films were also annealed at 400 °C for 2 min in air. The structural properties of the deposited films were characterized using X-ray diffraction and AFM. Formation of cubic structure with preferential orientation along the (111) plane was confirmed together with BiS second phase from structural analysis. The interplanar spacing, lattice constant, and crystallite size of (Cd_1?xBi_x)S thin films were calculated by the XRD. The crystallite size of the un-doped CdS thin films was found to be 7.84 nm, which increased to 11.1 nm with increasing Bi content from 0 to 10 %. The surface roughness of the films was measured by AFM studies. The photoluminescence spectra were observed at red shifted band edge peak with increasing doping concentration of Bi from 0 to 5 % in the un-doped CdS thin films. The optical properties of the films are estimated using optical absorption and transmission spectra in the range of 400–800 nm using UV–VIS spectrophotometer. The optical band gap energy of the films was found to be decreased from 2.44 to 2.23 eV with the Bi content being from 0 to 5 %. After annealing, the band gap of these films further decreased.     

Electrical and optical properties of MoSe2 films prepared by r.f. magnetron sputtering

The electrical resistivity of MoSe₂ films prepared by r.f. magnetron sputtering was measured between 300 and 10 K. The main sputtering parameter governing the physical properties of the films was found to be the substrate temperature T_sub. The room temperature resistivity of the as-sputtered films increased from $\text{1.7 × 10}{}^{-1}\text{Ω}\text{cm}$(T_sub = -70 °C) to $\text{1.4 × 10}{}^1\text{Ω}\text{cm}\text{(T}{}_{\mathrm{<mtext>sub</mtext>}}\text{= 150 °}\text{C}\text{)}$. A check of the thermo-electrical response showed that the majority charge carriers are holes except for films deposited at T_sub = 150 °C which are n type. Hall effect measurements indicated very low Hall mobilities (3–5 cm² V^-1 s^-1). Thermal annealing increased the room temperature resistivities by more than one order of magnitude for the specimens sputtered at a low substrate temperature. The optical properties were weakly influenced by the process conditions. The optical gap was determined to be 1.06 eV.     

Effects of growth temperature on electrical and structural properties of sputtered GaN films with a cermet target

GaN films have been deposited at 100–400 °C substrate temperature on Si (100) and sapphire (0001) substrates by RF reactive sputtering in an (Ar + N₂) atmosphere. A (Ga + GaN) cermet target for sputtering was made by hot pressing the mixed powders of metallic Ga and ceramic GaN. The effects of substrate temperature on the GaN formation and its properties were investigated. The diffraction results showed that GaN films with a preferential (10–10) growth plane had a wurtzite crystalline structure. GaN films became smoother at higher substrate temperature. The Hall effect measurements showed the electron concentration and mobility were 1.04 × 10¹⁸ cm^?3 and 7.1 cm² V^?1 s^?1, respectively, for GaN deposited at 400 °C. GaN films were tested for its thermal stability at 900 °C in the N₂ atmosphere. Electrical properties slightly degraded after annealing. The smaller bandgap of ~3.0 eV is explained in terms of intrinsic defects and lattice distortion.     

The compositional and structural properties of sprayed SnO2:F thin films

Thin films of SnO₂ doped with fluorine were produced by the conventional spraying method using Corning 7059 glass substrates. The electrical and optical properties of these films were determined as a function of the substrate temperature T_s and dopant concentration in the basic spraying solution. The visible and near-IR transmittance as well as the electrical resistivity of the films decreased with an increase in the fluorine concentration. The best electro-optical properties (an average transmittance of 75% and an electrical resistivity of 10⁻³ Ω cm) were achieved for 250°C⩽T_s⩽350°C and fluorine concentrations (relative to tin) in the spraying solution of around 2 at.%. The surface texture of the films was investigated by scanning electron microscopy and optical microscopy. The fluorine content of the samples was analysed by secondary ion mass spectroscopy, Auger electron spectroscopy and electron spectroscopy for chemical analysis. Structural changes were studied using X-ray diffractometry. A systematic change in the intensity of the X-ray diffraction lines as a function of the fluorine content was observed. Theoretical calculations of the structure factors associated with the SnO₂ lattice if fluorine atoms are introduced into substitutional and interstitial positions were performed.     

The epitaxial growth of germanium and silicon on an Ag(111) film on a mica substrate

With the aim of finding a method of obtaining self-supporting single-crystal films of silicon for solar cells we studied the epitaxial growth of silicon and germanium prepared by evaporation in ultrahigh vacuum onto an Ag(111) film evaporated in situ onto a mica substrate cleaved in air. The films were examined mainly by reflection high energy electron diffraction. Silicon and germanium films 50–200 Å thick were composed of crystallites with two main orientations relative to the substrate and unoriented crystallites in varying proportions depending on the substrate temperature T_s and the previous heat treatment temperature T_H of the mica. Nearly single-crystal films of silicon could be obtained for T_s = 350 °C and T_H = 250 °C. The sticking coefficient for silicon on silver was found to decrease almost to zero for T_s = 420 °C with T_H = 250 °C. No single-crystal films of germanium were obtained.     

Characterization and photocatalytic activity of boron-doped TiO<Subscript>2</Subscript> thin films prepared by liquid phase deposition technique

Boron doped TiO₂ thin films have been successfully deposited on glass substrate and silicon wafer at 30°C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F ⁻ scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500°C. The EDAX and XRD data confirm the existence of boron atom in TiO₂ matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO₂ thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO₂ thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concentration of boron.     

Properties of electron-beam-evaporated tin oxide films

Transparent conducting thin films of tin oxide were prepared by electron beam evaporation of sintered pellets of SnO₂ under controlled conditions. Variations in such parameters as the substrate temperature T_s and the post-deposition annealing temperature T_A and time t_A were studied. Structural, electrical and optical properties were measured to characterize the films. The film structure changed gradually from amorphous to crystalline (SnO phase) as T_S was varied from 150 to 350 °C. A sharp decrease in the room temperature resistivity together with the growth of a crystalline phase occured in the as-deposited films at T_S ≈ 250°C. On annealing in air (T_A = 550°C, t_A = 2 h) a radical structural transformation from amorphous to crystalline occurred with a sharp fall in resistivity for T_S ⩽ 225°C. For T_S = 350°C the lowest resistivity achieved for the undoped annealed films was 6.6×10^-3 Ω cm, the average visible transmittance was about 90% and the structure was characteristic of pure SnO₂.     

Low indium content In–Zn–O system towards transparent conductive films: structure,properties and comparison with AZO and GZO

In this work, low content indium doped zinc oxide (IZO) thin films were deposited on glass substrates by RF magnetron sputtering using IZO ceramic targets with the In₂O₃ doping content of 2, 6, and 10 wt%, respectively. The influences of In₂O₃ doping content and substrate temperature on the structure and morphology, electrical and optical properties, and environmental stability of IZO thin films were investigated. It was found that the 6 wt% doped IZO thin film deposited at 150?°C exhibited the best crystal quality and the lowest resistivity of 9.87?×?10^?4 Ω cm. The corresponding Hall mobility and carrier densities were 9.20 cm² V^?1 s^?1 and 6.90?×?10²⁰ cm^?3, respectively. Compared with 2 wt% Al₂O₃ doped ZnO and 5 wt% Ga₂O₃ doped ZnO thin films, IZO thin film with the In₂O₃ doping content of 6 wt% featured the lowest surface roughness of 1.3 nm. It also showed the smallest degradation with the sheet resistance increased only about 4.4% at a temperature of 121?°C, a relative humidity of 97% for 30 h. IZO thin film with 6 wt% In₂O₃ doping also showed the smallest deterioration with the sheet resistance increased only about 2.8 times after heating at 500?°C for 30 min in air. The results suggested that low indium content doped ZnO thin films might meet practical requirement in environmental stability needed optoelectronic devices.     

Intrinsic defects and structural phase of ZnS nanocrystalline thin films: effects of substrate temperature

Fabrications of ZnS nanocrystalline thin films at different substrate temperatures (T_S) of 200, 300 and 400 °C by means of pulsed laser deposition are presented. Thin film deposited at T_S of 200 °C is in cubic zinc-blende (ZB) structure while those deposited at T_S of 300 and 400 °C are in hexagonal wurtzite (W) phase. The grain size, surface roughness and bandgap of the films increases with increasing T_S. The zinc vacancies and interstitials in the films increases while sulfur vacancies decreases with increasing T_S. The variation of zinc and sulfur vacancies in ZnS films with T_S is responsible for structural phase transition from ZB to W which causes the change in energy bandgap.     

Substrate temperature dependent physical properties of sprayed Zn0.76Mg0.24O films

The composition, microstructural and opto-electronic properties of Zn_1?x Mg _x O thin films grown by spray pyrolysis have been studied. The films were prepared on glass substrates at different substrate temperatures in the range, 200–350 °C for a fixed magnesium composition of x = 0.24. The films showed the predominant (002) reflection corresponding to the hexagonal wurtzite structure of ZnO. The preferred orientation doesn’t change with the deposition temperature. The films prepared at 300 °C showed good crystallinity with an average surface roughness of 6.2 nm. The optical studies revealed that the optical transmittance increased slightly with the increase of substrate temperature of the films. The variation of energy band gap, photoluminescence and electrical resistivity of the grown layers was also studied.     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

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

The effect of the substrate temperature on the properties of spray-deposited SnO₂:F thin films is investigated. X-ray diffraction patterns show that the crystallinity of the films is enhanced with the increasing of substrate temperature. Comparing the SEM images, both the particle size and density are increased at a higher deposition temperature. The lowest sheet resistance of 8.43 Ω/□ is obtained at the substrate temperature of 350 °C. In addition, the average optical transmittance of the three films reaches up to 85 % in the visible range. The absorption coefficient is the lowest at 350 °C. The band gap increases from 3.36 to 3.61 eV while the electrical resistivity of SnO₂:F thin films decreases from 8.51 × 10^?3 to 9.86 × 10^?4 Ω cm as elevating the substrate temperature from 250 to 350 °C.     

Dependence of structural, optical and electrical properties on substrate temperature for hexagonal MgxZn1−xO films

Single hexagonal-phase Mg_xZn_1?xO films were deposited on glass substrates by pulsed laser deposition from a ZnO target mixed with MgO. The effect of substrate temperature on the structural, electrical and optical properties was investigated by X-ray diffraction and the transmittance measurements. It was observed that Mg incorporation lead to a clear shift of the (002) peak position to lower angle with reference to pure ZnO films due to the residual stress change with deposition temperature. It was also found that Mg doping increased the resistivity by 2 orders of magnitude and the maximum resistivity was 0.072 Ω·cm at 550 °C with the carrier concentration of 1.1 × 10¹⁹ cm^?3. The visible transmittance of above 80 % was obtain in the alloy films, which optical band gap was observed to increase with the substrate temperature, attaining 3.85 eV at 600 °C. The possible mechanism was discussed.