Impact of growth temperature on the properties of SnS film prepared by thermal evaporation and its photovoltaic performance

Tin(II) sulfide (SnS) films are one of the most promising absorber materials for high efficiency solar cells without using rare metals. In this work, SnS films were deposited by the thermal evaporation on glass substrates under the variation of growth temperatures of 100–250 °C. It was revealed that the SnS thin film prepared under the temperature of 100 °C had relatively small crystal grains. On the other hand, the denser and larger crystal grains of the SnS films were obtained with the constant compositions, when the growth temperature increased to 225 °C. With the temperature of higher than 225 °C, the SnS began to be re-evaporated from the films. The highest Hall mobility of the films was obtained under the temperature of 200 °C. Ultimately, the results suggested that the optimized growth temperature of SnS by the evaporation is 200 °C, giving rise to compact and large crystal grains and the highest Hall mobility, thereby contributing to the 2.53%-efficient SnS thin-film solar cell.     

Structural and optical properties of Mn-doped ZnO nanocrystalline thin films with the different dopant concentrations

The transparent nanocrystalline thin films of undoped zinc oxide and Mn-doped (Zn_1−xMn_xO) have been deposited on glass substrates via the sol–gel technique using zinc acetate dehydrate and manganese chloride as precursor. The as-deposited films with the different manganese compositions in the range of 2.5–20 at% were pre-heated at 100 °C for 1 h and 200 °C for 2 h, respectively, and then crystallized in air at 560 °C for 2 h. The structural properties and morphologies of the undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/Vis spectroscopy. The analyzed results indicates that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn related phases. Room temperature photoluminescence is observed for the ZnO and Mn-doped ZnO thin films.     

Structural and optical properties of pulsed laser deposited ZnO thin films

Nanocrystalline ZnO thin films were grown by means of pulsed laser deposition. The ablation process was carried out at relatively low background oxygen gas pressure (10 Pa) and by varying the substrate temperature up to 600 °C. Information on the structural and morphological properties of the deposited thin films have been obtained by means of X-ray photoelectron, Raman spectroscopies, X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed that all the deposited films are sub-stoichiometric in oxygen and with a hexagonal wurtzite crystalline structure, characterized by features of some tens of nanometers in size. An improvement of the films' crystalline quality was observed for the deposition temperature of 300 °C while the further increase of the deposition temperature up to 600 °C induces a worsening of the material's structural properties with the development of a large amount of nanoparticle's clusters. The analysis of the XRD patterns shows a growth crystallographic preferential direction as a function of the deposition temperature, in agreement with the appearance of the only E₂ optical phonon mode in the Raman spectra. Such findings are compatible with the changes observed in the photoluminescent (PL) optical response and was related to the modification of the ZnO thin film structural quality.     

Nonlinear optical properties of erbium doped zinc oxide (EZO) thin films

Undoped and Erbium (Er) doped zinc oxide (EZO) thin films were deposited on glass substrate by sol–gel method using spin coating technique with different doping concentration. EZO films were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), UV–VIS-NIR transmission and single beam z scan method under illumination of frequency doubled Nd:YAG laser. The deposited films were found to be well crystallized with hexagonal wurtzite structure having a preferential growth orientation along the ZnO (002) plane. A blue-shift was observed in the band gap of EZO films with increasing Er concentration. All the films exhibited a negative value of nonlinear refractive index (n₂) at 532 nm which is attributed to the two photon absorption and weak free carrier absorption. Third order nonlinear optical susceptibility, χ⁽³⁾ values of EZO films were observed in the remarkable range of 10^? 6 esu. EZO (0.4 at.%) sample was found to be the best optical limiter with limiting threshold of 1.95 KJ/cm².     

Substitution mechanism of Ga for Zn site depending on deposition temperature for transparent conducting oxides

High quality transparent conductive gallium-doped zinc oxide (GZO) thin films were deposited on glass substrates using rf-magnetron sputtering system at the temperature ranging from room temperature (RT) to 500 °C. The temperature-dependence of Ga doping effect on the structural, optical and electrical properties in ZnO has been investigated. For the GZO thin films deposited at over 200 °C, (103) orientation was strongly observed by X-ray diffraction analysis, which is attributed to the substitution of Ga elements into Zn site. X-ray photoelectron spectroscopy measurements have confirmed that oxygen vacancies were generated at the temperature higher than 300 °C. This might be due to the effective substitution of Ga³⁺ for Zn site at higher temperature. It was also found that the optical band gap increases with deposition temperature. The optical transmittance of GZO thin films was above 87% in the visible region. The GZO thin films grown at 500 °C showed a low electrical resistivity of 4.50 × 10^?4 Ω cm, a carrier concentration of 6.38 × 10²⁰ cm^?3 and a carrier mobility of 21.69 cm²/V.     

Effect of annealing temperature on the characteristics of ZnO thin films

Effect of annealing temperature on characteristics of sol–gel driven ZnO thin film spin-coated on Si substrate was studied. The UV–visible transmittance of the sol decreased with the increase of the aging time and drastically reduced after 20 days aging time. Granular shape of ZnO crystallites was observed on the surface of the films annealed at 550, 650, and 750 °C, and the crystallite size increased with the increase of the annealing temperature. Consequently nodular shape of crystallites was formed upon increasing the annealing temperature to 850 °C and above. The current–voltage characteristics of the Schottky diodes fabricated with ZnO thin films with various annealing temperatures were measured and analyzed. It is found that, ZnO films showed the Schottky characteristics up to 750 °C annealing temperature. The Schottky diode characteristics were diminished upon increasing the annealing temperature above 850 °C. XPS analysis suggested that the absence of oxygen atoms in its oxidized state in stoichiometric surrounding, might be responsible for the diminished forward current of the Schottky diode when annealed above 850 °C.     

High c-axis preferred orientation ZnO thin films prepared by oxidation of metallic zinc

Thin films of zinc oxide were grown on glass substrates by thermal oxidation. The metallic zinc films were thermally oxidized at different temperatures ranging from 300 to 600 °C to yield ZnO thin films. The structural property of the thin films was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction measurements showed that the films oxidized at 300 °C were not oxidized entirely, and the films deposited at 600 °C had better crystalline quality than the rest. When the oxidation temperature increased above 400 °C, the films exhibited preferred orientation along (002) and high transmittance ranging from 85% to 98% in vis–near-infrared band. Meanwhile, the films showed a UV emission at about 377 nm and green emission. With the increasing of oxidation temperature, the intensity of green emission peak was enhanced, and then decreased, disappearing at 600 °C, and the case of UV emission increased. Furthermore, a strong green emission was observed in the film sintered in pure oxygen atmosphere.     

Optical properties of amorphous HF–In–Zn–O thin films estimated from transmission spectra

Amorphous and flat (<1 nm roughness) Hf–In–Zn–O thin films were prepared by radio frequency (rf) magnetron sputtering method at room temperature (RT) and at 300 °C substrate temperature. The crystal structure and surface morphology were investigated by high resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM), respectively. Optical properties of these films were obtained from the UV–VIS–NIR transmission spectra, at normal incidence, over the 200–2000 nm spectral range. Swanepoel's method was used to calculate the thickness and the refractive index of the films. The dispersion of refractive index was obtained in terms of the single-oscillator Wemple–DiDomenico model. The optical absorption edge was described using the direct transition model proposed by Tauc. The film deposited at higher substrate temperature had lower optical band gap, higher refractive index, higher oscillator strength and energy of the effective dispersion oscillator. Optical characterization shows that films become more stable, relaxed and rigid at higher substrate temperature.     

Influence of annealing temperature on optical properties of zinc oxide thin films analyzed by spectroscopic ellipsometry method

Zinc oxide (ZnO) thin films were sol–gel spin coated on glass substrates, annealed at various temperatures 300 °C, 400 °C and 500 °C and characterized by spectroscopic ellipsometry method. The optical properties of the films such as transmittance, refractive index, extinction coefficient, dielectric constant and optical band gap energy were determined from ellipsometric data recorded over the spectral range of 300–800 nm. The effect of annealing temperature in air on optical properties of the sol–gel derived ZnO thin films was studied. The transmission values of the annealed films were about 65% within the visible range. The optical band gap of the ZnO thin films were measured between 3.25 eV and 3.45 eV. Also the dispersion parameters such as single oscillator energy and dispersive energy were determined from the transmittance graph using the Wemple and DiDomenico model.     

Structural,optical, and electrical properties of tin sulfide thin films grown with electron-beam evaporation

The effect of growth temperature on the phase evolution and morphology change of tin sulfide thin films by electron-beam evaporation was investigated. Orthorhombic tin monosulfide (SnS) was dominant at low growth temperature of 25 °C, whereas a sulfur-rich phase of Sn₂S₃ coalesced as the growth temperature increased over 200 °C. Thin film growth ceased at 280 °C due to re-evaporation of the tin sulfide. The dependence of growth temperature on the phase evolution of tin sulfide was confirmed by X-ray diffraction, scanning electron microscopy, and UV–Vis spectrophotometry. The lowest electrical resistivity of ∼51 Ω cm, with a majority hole concentration of ∼10¹⁷ cm⁻³, was obtained for the film grown at 100 °C, and the resistivity drastically increased with increasing growth temperature. This behavior was correlated with the emergence of resistive sulfur-rich Sn₂S₃ phase at high temperatures.     

Characteristics of ZnO:In thin films prepared by RF magnetron sputtering

In-doped ZnO (ZnO:In) transparent conductive thin films were deposited on glass substrates by RF magnetron sputtering. The effect of substrate temperature on the structural, electrical and optical properties of the ZnO:In thin films was investigated. It was found that higher temperature improves the crystallinity of the films and promotes In substitution easily. ZnO:In thin films with the best crystal quality were fabricated at 300 °C, which exhibit a larger grain size of 29 nm and small tensile strain of 0.9%. The transmittance of all the films was revealed to be over 85% in the visible range independence of the substrate temperatures and the lowest resistivity of ZnO:In thin films is 2.4×10⁻³ Ω cm.     

Comparative study on structural and optical properties of ZnO thin films prepared by PLD using ZnO powder target and ceramic target

Zinc oxide thin films have been obtained in O₂ ambient at a pressure of 1.3 Pa by pulsed laser deposition (PLD) using ZnO powder target and ceramic target. The effect of temperature on structural and optical properties of ZnO thin films was investigated systematically by XRD, SEM, FTIR and PL spectra. The results show that the best structural and optical properties can be achieved for ZnO thin film fabricated at 700 °C using powder target and at 400 °C using ceramic target, respectively. The PL spectrum reveals that the efficiency of UV emission of ZnO thin film fabricated by using powder target is low, and the defect emission of ZnO thin film derived from Zn_i and O_i is high.     

Highly frequency-, temperature-, and bias-stable dielectric properties of 500 °C processed Bi2SiO5 thin films with low dielectric loss

Excellent dielectric frequency, bias, and temperature stability of bismuth silicate (Bi₂SiO₅, BSO) thin films with a low dielectric loss has been obtained in this study. The thin films were prepared on Pt/Ti/SiO₂/Si substrates by a chemical solution deposition method at a relatively low annealing temperature of 500 °C. The BSO films have a preferred growth along (200) orientation with dense fine-grained surface morphology. The dielectric constant and dielectric loss of the thin film annealed at 500 °C are 57 and 0.01, respectively, at 100 kHz, with little change between 1 kHz and 100 kHz and in the bias electric field range between −250 kV/cm and 250 kV/cm, indicating that the thin film exhibits a low dielectric loss as well as excellent frequency and bias field stability. The dielectric-temperature measurements confirmed that the BSO thin film annealed at 500 °C also has good temperature stability between 150 K and 450 K. Our results suggest that the BSO thin films have potential applications in the next-generation integrated capacitors.     

Structural and optical properties of ZnO thin films deposited on quartz glass by pulsed laser deposition

ZnO thin films with typical c-axis (0 0 2) orientation were successfully deposited on quartz glass substrates by pulse laser ablation of Zn target in oxygen atmosphere at a relatively low temperature range of 100-250 °C. The structural and optical properties of the films were studied. In photoluminescence (PL) spectra at room temperature, single ultraviolet emission (without deep-level emission) was obtained from ZnO film deposited at the temperature of 200 °C. This was attributed to its low intrinsic defects.     

Optical properties of PMN–PT thin films prepared using pulsed laser deposition

(1 ? x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–PT) thin films have been deposited on quartz substrates using pulsed laser deposition (PLD). Crystalline microstructure of the deposited PMN–PT thin films has been investigated with X-ray diffraction (XRD). Optical transmission spectroscopy and Raman spectroscopy are used to characterize optical properties of the deposited PMN–PT thin films. The results show that the PMN–PT thin films of perovskite structure have been formed, and the crystalline and optical properties of the PMN–PT thin films can be improved as increasing the annealing temperature to 750 °C, but further increasing the annealing temperature to 950 °C may lead to a degradation of the crystallinity and the optical properties of the PMN–PT thin films. In addition, a weak second harmonic intensity (SHG) has been observed for the PMN–PT thin film formed at the optimum annealing temperature of 750 °C according to Maker fringe method. All these suggest that the annealing temperature has significant effect on the structural and optical properties of the PMN–PT thin films.     

Effects of preannealing temperature of ZnO thin films on the performance of dye-sensitized solar cells

The preferred (002) orientation zinc oxide (ZnO) nanocrystalline thin films have been deposited on FTO-coated glass substrates by sol–gel spin-coating technology and rapid thermal annealing for use in dye-sensitized solar cells (DSSC). The effects of preannealing temperature (100 and 300°C) on the microstructure, morphology and optical properties of ZnO thin films were studied. The ZnO thin films were characterized by X-ray diffraction (XRD), scanning electron microscopic (SEM) and Brunauer–Emmett–Teller (BET) analysis. The photoelectric performance of DSSC was studied by I–V curve and the incident photon-to-current conversion efficiency (IPCE), respectively. From the results, the intensities of (002) peaks of ZnO thin films increases with increasing preannealing temperature from 100°C to 300°C. The increase in pore size and surface area of ZnO films crystallized at the increased preannealing temperature contributed to the improvement on the absorption of N3 dye onto the films, the short-circuit photocurrent (J _sc) and open-circuit voltage (V _oc) of DSSC. The higher efficiency (η) of 2.5% with J _sc and V _oc of 8.2 mA/cm² and 0.64 V, respectively, was obtained by the ZnO film preannealed at 300°C.     

Raman characterization before and after rapid thermal annealing of CeO2 thin films grown by rf sputtering on (111) Si

We investigated by Raman spectroscopy (RS) the crystalline quality of CeO₂ thin films radio frequency magnetron sputtered on n‐type (111) Si substrates from CeO₂ target. The deposition temperature was in the range of 200–800 °C. We also realized structural investigations on CeO₂ layers after Rapid Thermal Annealing (RTA) performed in the range of 750–1000 °C for 30 s under nitrogen atmosphere. So this study displays that a high‐growth temperature and a high post‐growth‐RTA temperature improves the crystalline structure of the film. In fact, the best crystalline quality, which is close to the CeO₂ target taken as a reference, is obtained for a CeO₂ layer deposited at 800 °C and post‐annealed at 1000 °C for 30 s. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface morphology of ZnO buffer layer and its effects on the growth of GaN films on Si substrates by magnetron sputtering

ZnO thin films were first prepared on Si(111) substrates using a radio frequency magnetron sputtering system. Then the as-grown ZnO films were annealed in oxygen ambient at temperatures of 700, 800, 900, and 1000°C , respectively. The morphologies of ZnO films were studied by an atom force microscope (AFM). Subsequently, GaN epilayers about 500 nm thick were deposited on the ZnO buffer layers. The GaN/ZnO films were annealed in NH₃ ambient at 900°C. The microstructure, morphology and optical properties of GaN films were studied by x-ray diffraction (XRD), AFM, scanning electron microscopy (SEM) and photoluminescence (PL). The results are shown, their properties having been investigated particularly as a function of the ZnO layers. For better growth of the GaN films, the optimal annealing temperature of the ZnO buffer layers was 900°C.     

The reason of degradation in electrical properties of ZnO:Al thin films annealed with various post-annealing temperature

ZnO:Al (AZO) thin films were deposited on glass substrates by RF magnetron sputtering at room temperature and post-annealed in rapid thermal annealing (RTA) system. The effect of post-annealing temperature on the structural, optical, and electrical properties was investigated. As the post-annealing temperature increased, electrical conductivity is deteriorated due to a decrease in the mobility or carrier concentration, gradually. According to X-ray photoelectron spectroscopy (XPS) analysis, the behavior of mobility and carrier concentration is attributed to increase the O₂ absorption on film surface, which act as rising the barrier potential at the low post-annealing temperature (200 °C) and reducing the density of donor-like defects at the high post-annealing temperature (400 °C). In case of post-annealing, the minimization of O₂ absorption is a very important factor to obtain better electrical properties.     

Nitrogen incorporation in homoepitaxial ZnO CVD epilayers

ZnO:N thin films have been deposited on oxygen and zinc terminated polar surfaces of ZnO. The nitrogen incorporation in the epilayers, using NH₃ as doping source, was investigated as a function of the growth temperature in the range between 380 °C and 580 °C. We used Raman spectroscopy and low temperature photoluminescence to investigate the doping properties. It turned out that the nitrogen incorporation strongly depends on both, the surface polarity of the epitaxial films and the applied growth temperatures. In our CVD process low growth temperatures and Zn‐terminated substrate surfaces clearly favour the nitrogen incorporation in the ZnO thin films. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)