Preparation of cadmium stannate films by spray pyrolysis technique

Cadmium stannate thin films were prepared by spray pyrolysis technique using cadmium acetate and tin(II) chloride precursors at substrate temperatures 450 °C and 500 °C. XRD pattern confirms the formation of orthorhombic (1 1 1) cadmium stannate phase for the film prepared at substrate temperature of 500 °C, whereas, films prepared at 450 °C are amorphous. Film formation does not occur at substrate temperature from 300 to 375 °C. SEM images reveal that the surface of the prepared Cd₂SnO₄ film is smooth. The average optical transmittance of ∼86% is obtained for the film prepared at substrate temperature of 500 °C with the film thickness of 400 nm. The optical band gap value of the films varies from 2.7 to 2.94 eV. The film prepared at 500 °C shows a minimum resistivity of 35.6 × 10⁻⁴ Ω cm.     

Role of deposition temperature and Sn content on structural,optical & electrical properties of In2O3 thin films

High quality indium tin oxide (ITO) thin films (In_2−xSn_xO₃: x = 0, 0.1 and 0.2) have been grown by using pulsed laser deposition technique on quartz substrates. The structural, morphological, optical and electrical investigations of deposited films have been studied as a function of substrate deposition temperatures and the Sn compositions. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) patterns affirm that each film is polycrystalline in nature with cubic bixbyite single phase structure which preferentially oriented along (222) Miller plane. The existence of chemical bonding and functional groups was investigated by FTIR spectroscopy. The TEM micrograph of films (@450°C) for x = 0.1 and x = 0.2 reveal spherical morphology with average particle size 63 nm and 51 nm, respectively. The SEM and AFM images show uniform flower like surface morphology and well-demonstrated nanosized spherical particles, respectively. The widening of the band gap of all the films were exclusively defined by Burstein-Moss shift. The Hall measurement reveals that each film is degenerate with n-type semiconducting nature along with high mobility. Low resistivity (2.024 × 10⁻⁴ Ω-cm) and high transparency (92.58%) along with high carrier concentration (8.915 × 10²⁰ cm⁻³) were optimized for x = 0.1 film at 450°C deposition temperature.     

Development of sulphurized SnS thin film solar cells

Thin films of tin sulphide (SnS) have been grown by sulphurization of sputtered tin precursor layers in a closed chamber. The effect of sulphurization temperature (T_s) that varied in the range of 150–450 °C for a fixed sulphurization time of 120 min on SnS film was studied through various characterization techniques. X-ray photoelectron spectroscopy analysis demonstrated the transformation of metallic tin layers into SnS single phase for T_s between 300 °C and 350 °C. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. Raman analysis showed modes at 95 cm⁻¹, 189 cm⁻¹ and 218 cm⁻¹ are related to the A_g mode of SnS. AFM images revealed a granular change in the grain growth with the increase of T_s. The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.2 eV to 1.6 eV with T_s. The Hall effect measurements showed that all the films were p-type conducting nature and the layers grown at 350 °C showed a low electrical resistivity of 64 Ω-cm, a net carrier concentration of 2 × 10¹⁶ cm⁻³ and mobility of 41 cm² V⁻¹ s⁻¹. With the use of sprayed Zn_0.76Mg_0.24O as a buffer layer and the sputtered ZnO:Al as window layer, the SnS based thin film solar cell was developed that showed a conversion efficiency of 2.02%.     

Characterization of Cd1−xFexS diluted magnetic semiconductors grown at near phase conversion temperature

Fe-based cadmium sulfide alloy thin films have been grown on c-plane sapphire substrates by a low-pressure metalorganic chemical vapor deposition technique at different growth temperatures. From X-ray diffraction and absorption spectra of the samples, the evolutions with growth temperature show an inflexion at the growth temperature of 300 ^°C. This was attributed to the phase transformation from zinc-blende to wurtzite. With increasing growth temperature from 270 ^°C to 360 ^°C, Fe concentration in the films increases monotonously. The electronic states of Cd_1−xFe_xS were investigated by X-ray photoelectron spectroscopy. Magnetic measurement shows Van Vleck paramagnetism of the Cd_1−xFe_xS thin film in the temperature region below 7 K.     

Investigation of Cu2ZnSnS4 solar cell buffer layer fabricated via spray pyrolysis

Copper zinc tin sulfide solar cells were fabricated by using spray pyrolysis from a window layer to an absorber layer. ZnS and In₂S₃ buffer layers were deposited on the TiO₂ layer, and the photovoltaic characteristics were investigated. The ZnS buffer demonstrated a poor photovoltaic performance because of its poor surface coverage and micro-cracks at fluorine-doped tin oxide/TiO₂ layers. The In₂S₃ buffer layer sprayed at low temperature (<360 °C) showed a large difference between photo and dark currents beyond the open-circuit voltage (V_OC). When the spraying temperature exceeded 390 °C, the devices showed high dark leakage currents at reverse biases because of the high conductivity of the buffer layer, resulting in decreased V_OC and short-circuit current density (J_SC). The optimum temperature for spraying In₂S₃ is 360 °C, and the best performing device showed 410 mV, 30.4 mA/cm², 35.3%, and 4.4% of V_OC, J_SC, fill factor, and efficiency, respectively.     

Effects of deposition temperature and post-annealing on structure and electrical properties in (La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>)CoO<Subscript>3</Subscript> films grown on silicon substrate

(La_0.5Sr_0.5)CoO₃ (LSCO) thin films have been fabricated on silicon substrate by the pulsed laser deposition method. The effects of substrate temperature and post-annealing condition on the structural and electrical properties are investigated. The samples grown above 650°C are fully crystalline with perovskite structure. The film deposited at 700°C has columnar growth with electrical resistivity of about 1.99×10⁻³ Ω cm. The amorphous films grown at 500°C were post-annealed at different conditions. The sample post-annealed at 700°C and 10⁻⁴ Pa has similar microstructure with the sample in situ grown at 700°C and 25 Pa. However, the electrical resistivity of the post-annealed sample is one magnitude higher than that of the in situ grown sample because of the effect of oxygen vacancy. The temperature dependence of resistivity exhibits semiconductor-like character. It was found that post-annealing by rapid thermal process will result in film cracks due to the thermal stress. The results are referential for the applications of LSCO in microelectronic devices.     

Photoluminescence study of nitrogen-doped p-type Mg x Zn1−x O nanocrystalline thin film grown by plasma-assisted molecular beam epitaxy

Tin sulfide thin films have been grown on glass substrates by chemical bath deposition technique (CBD) at room temperature and irradiated with UV light source of wavelength 355 nm. The effect of UV illumination on the physical properties of the films was compared with that of the as-prepared film. Though the thickness of the films was unaltered after illumination, the structural, optical and electrical properties changed considerably. Structural studies showed the polycrystalline nature of the UV-illuminated sample, whereas the as-prepared film was mono crystalline. Both films were orthorhombic structure with Sn₂S₃ phase. The optical properties of the films were systematically studied using the optical absorbance and reflection spectra. Studies on the reflection spectra showed higher reflectance in visible and infrared region for the UV-illuminated films and lower reflectance in the infrared region for the as-prepared one. The variation of the refractive index of the samples was also analyzed. The optical absorption coefficient and the optical band gap energy of the films were evaluated. The irradiated film exhibited lower band gap of 1.74 eV than the value of as-prepared film, i.e., 1.77 eV. The measured resistivity of the tin sulfide thin films was found to be of the order of 10⁸ and 10⁹ Ωcm for UV-illuminated and as-prepared films, respectively. The SEM images showed the presence of worm-like nanostructures with almost similar appearance in both the films.     

Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

The annealing effect on structural,optical and photoelectrical properties of CuInS2/In2S3 films

Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit the CuInS₂/In₂S₃ multilayer thin film structure at room temperature. The as-deposited film was annealed at 100, 200, 300, 400 and 500 °C for 30 min in nitrogen atmosphere and the annealing effect on structural, optical and photoelectrical properties of the film was investigated. X-ray diffraction (XRD) and optical absorption spectroscopy were used for structural and optical studies. Current–Voltage (I–V) measurements were performed in dark environment and under 15, 30 and 50 mW/cm² light intensity to investigate the photosensitivity of the structure. Also, the electrical resistivity of the film was determined in the temperature range of 300–470 K. It was found that annealing temperature drastically affects the structural, optical and photoelectrical properties of the CuInS₂/In₂S₃ films.     

Synthesis of tin oxides SnO2–x in the entire composition range (x = 0 to 1) by ion‐beam sputter‐deposition

Ion‐beam sputter‐deposition (IBSD) was used to reactively deposit tin oxide crystalline films at oxygen fluxes of 3–15 sccm and at substrate temperatures of 100–600 °C. Analysing the samples by X‐ray diffraction and Raman spectro‐ scopy yields a map of the crystalline structures in dependence on the growth parameters. In addition to SnO₂, pure SnO films of high quality and an intermediate phase such as Sn₂O₃ or Sn₃O₄ can be reproducibly obtained. Thus, IBSD is, to our knowledge, the only thin‐film deposition technique verified yet to reliably produce samples in the entire composition range of tin oxides. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Dopant distribution, oxygen stoichiometry and magnetism of nanoscale Sn0.99Co0.01O2

In recent work, we have shown that chemically synthesized Sn_1−xCo_xO₂ nanoscale powders with x≤0.01 are ferromagnetic at room temperature when prepared by annealing the reaction precipitate in the narrow temperature window of 350-600 ^°C. Combined high resolution x-ray photoelectron spectroscopy (on as-prepared and Ar⁺ ion sputtered samples), x-ray diffraction and magnetometry measurements showed that the Co distribution is more uniform throughout the individual Sn_0.99Co_0.01O₂ particles when prepared at lower annealing temperatures of 350-600 ^°C and this uniform dopant distribution is essential to produce stable high temperature ferromagnetism. However, surface segregation of the dopant atoms in samples annealed at >600 ^°C destroys the room-temperature ferromagnetic behavior and reduces the Curie temperature to <300 K.     

Microstructure control of low-resistivity tin-doped indium oxide films grown by photoreaction of nanoparticles using a KrF excimer laser at room temperature

A tin-doped indium oxide (ITO) film on a SiO₂ substrate was prepared by photo-irradiation of spin-coated nanoparticles using a Xe excimer lamp and a KrF excimer laser. The effects of the excimer lamp and the excimer laser on the resistivity, mobility, and carrier concentration of the film were investigated. To better understand how to control the microstructure of the film, we investigated the effect of thickness on the resistivity of a film prepared by the two-step process, and found that the resistivity was higher in a thicker film. Using two-step irradiation plus one-step KrF irradiation in N₂ at room temperature, we produced an ITO film with lowest resistivity of any in this study. The electrical resistivity of this film was 5.94×10⁻⁴ Ω cm. On the other hand, when using a simple thermal process, the resistivity of a film sintered at 500°C in N₂ was 4.10×10⁻³ Ω cm. The differences in resistivity are discussed on the basis of the microstructure of the films using atomic force microscopy and Hall measurements.     

A facile two-step preparation of compact and crystalline Sb2S3 thin film for efficient solar cells

The two-step preparation of compact and crystalline Sb₂S₃ thin films was firstly reported using the pyrolysis of the Sb-butyldithiocarbamate complex solution in DMF. The porous and amorphous Sb₂S₃ thin films were successfully prepared at 170 °C for 30 min, and then can be converted to compact and crystalline Sb₂S₃ thin films at 200 °C for 30 min or 300 °C for 2 min. The corresponding solar cells with the architecture of FTO/TiO₂ compact layer/Sb₂S₃/spiro-OMeTAD/Au achieved the photoelectric conversion efficiency of 4.16% at 200 °C and 5.05% at 300 °C. The two-step preparation of the compact and crystalline Sb₂S₃ thin films can provide the feasible approach for the fabrication of various microstructure thin film solar cells and the low preparation temperature of 200 °C was also attractive to assemble the flexible Sb₂S₃ thin film solar cells.     

Development of conductive transparent indium tin oxide (ITO) thin films deposited by direct current (DC) magnetron sputtering for photon-STM applications

Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95% indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10^-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range 3.0–5.7×10^-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities in the range 2.9–4.0×10^-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C, and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h. Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing time have been investigated. Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001     

The room-temperature ferromagnetism of defect-rich ZnMgO semiconductor thin films

The positive temperature coefficient of resistance (PTCR) characteristics of Na₂Ti₆O₁₃ (NT)-doped 0.94BaTiO₃–0.06(Bi_0.5Na_0.5)TiO₃ (BBNT) ceramics were investigated in order to evaluate the effect of NT as a new additive for lead-free PTCR thermistor application. The BBNT ceramic sintered at 1325°C exhibited a relatively high Curie temperature (T _C ) of 158°C while its PTCR characteristic was not satisfactory for thermistor application. However, doping with NT significantly influenced the PTCR behavior of BBNT ceramic. It is considered that NT was responsible for grain growth of the BBNT by forming a liquid phase during sintering due to its low melting temperature of 1300°C. The grain growth resulted in the enhanced PTCR characteristics of BBNT ceramic. In particular, 0.1 mol% NT doped BBNT ceramic exhibited excellent PTCR performance of low resistivity at room temperature (1.6×10² Ω cm), resistivity increase near T _C (1.28×10⁴) and high T _C of 158°C, suitable for lead-free PTCR thermistor application.     

Influence of substrate temperature on the electrical behaviour of zinc stannate thin films deposited by electron beam evaporation technique

Summary  A series of zinc stannate (Zn₂ SnO₄) thin films were prepared at four different substrate temperatures; namely, room-temperature (25°C), 50°C, 100°C and 200°C. Direct-current resistivity measurements were performed on these samples in the temperature range from room temperature (∼290 K) up to about 500 K. A phase transition (of positive temperature coefficient (PTC) of resistance) was observed in the thin film grown at room temperature at about 385 K. Other investigated samples showed a semiconducting behaviour of three distinct conduction mechanisms extending from intrinsic to thermal freeze-out conduction. The width of the band gapE _g was found to depend on the substrate temperature and was discussed in terms of a formation of a band tailing. Thermal freeze-out was dominant at the lower temperature region. On leave from Department of Physics, Faculty of Science, Alexandria University, Alexandria, Egypt.     

Electrical performance of Ti/Pt thin films on glass-ceramic substrates after high temperature loading

In this study, the influence of post-deposition annealings (PDA) up to temperatures of T _PDA=700°C on the room-temperature resistivity of e-beam evaporated titanium/platinum (Ti/Pt) bi-layers on low temperature co-fired (LTCC) substrates covered with a glass encapsulate is investigated. The thickness of the platinum top layer is varied between 24 and 95 nm (titanium film thickness: 5 nm) and between 23 and 90 nm (titanium film thickness: 15 nm), respectively. In the “as-deposited” state and up to post-deposition annealing temperatures of T _PDA=450°C, the film resistivity is linearly correlated with the reciprocal value of the platinum film thickness according to the size effect. When applying, however, solely the Fuchs-Sondheimer model for evaluation, the effective mean free path for electrons is substantially above the value reported for crystalline platinum at room temperature. Compared to similar investigations on smooth Si/SiO₂ substrates yielding interpretable results within this theoretical approach, this is due to the increase of the thickness-dependent fraction in film resistivity which is strongly affected by the enhanced LTCC/glass surface roughness. At T _PDA>600°C, diffusion of titanium into the platinum top layer and the roughening of the LTCC/glass substrate dominate the electrical behavior, both causing an increase in film resistivity above average. In contrast to Si/SiO₂ substrates, thermal induced grooving effects in the Pt top layer play a minor role as the temperature coefficients of expansion of metallization and glass-ceramic substrate match better and the effective temperature difference for stress generation is lower due a glass softening temperature of about 450°C.     

Structure,stability and electrical properties of the La(2−x)SrxMnO4±δ solid solution series

Single phase materials of the La_(2−x)Sr_xMnO_4±δ (0.6 ≤ x ≤ 2.0) solid solution series were prepared via solid state reaction. The structure of each material was examined at room temperature and determined to be tetragonal for all phases examined. An expansion in lattice volume was observed on increasing lanthanum content. The stability and thermal expansion of each member of the solid solution series was determined via the use of in situ high temperature X-ray diffraction. It was found that all materials remained stable up to a temperature of 800 °C. Thermal expansion coefficients were found to be in the region of 15 × 10^− 6 K^− 1 for La_(2−x)Sr_xMnO_4±δ compounds where x > 1.4. The electrical conductivity of each phase was also determined over a similar temperature range with a maximum value of ∼6 Scm^− 1 at 900 °C for the x = 1.8 phase.     

Damp heat and thermal cycling-induced degradation mechanism of AZO and CIGS films in Cu(In,Ga)Se2 photovoltaic modules

This paper characterizes and compares the degradation mechanisms of Cu(In,Ga)Se₂ (CIGS)-based thin film photovoltaic (PV) modules during exposure to damp heat (85 °C/85% RH) for 1000 h and thermal cycling (−40 °C/85 °C) for 1000 cycles. After damp heat (DH) exposure, the efficiency of the PV modules was reduced from the initial value of ∼12.5 ± 0.1% to 10.5 ± 0.2% due to increase of the resistivity in the AZO and CIGS layers. The optical band gap was also decreased from the initial value of 3.60 eV–3.54 eV after 1000-h DH exposure. This behavior was associated with oxygen adsorption and the generation of hydroxides in the AZO layer. The efficiency of the PV modules after subjection to thermal cycling (TC) was decreased to 11.4 ± 0.2% due to increase of the resistivity of the AZO and CIGS layers. The increase in the resistivity was interpreted as being due to oxygen adsorption, as well as the formation of micro-cracks in the AZO films.     

Measurement of surface resistivity and surface conductivity of anodised aluminium by optical interferometry techniques

Optical interferometry techniques were used for the first time to measure the surface resistivity and surface conductivity of anodised aluminium samples in aqueous solution, without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out in different sulphuric acid solutions (1.0–2.5% H₂SO₄), by the technique of electrochemical impedance spectroscopy (EIS), at room temperature. In the mean time, the real-time holographic interferometric was carried out to measure the thickness of anodised (oxide) film of the aluminium samples during the anodization process. Then, the alternating current (AC) impedance (resistance) of the anodised aluminium samples was determined by the technique of electrochemical impedance spectroscopy (EIS) in different sulphuric acid solutions (1.0–2.5% H₂SO₄) at room temperature. In addition, a mathematical model was derived in order to correlate between the AC impedance (resistance) and to the surface (orthogonal) displacement of the samples in solutions. In other words, a proportionality constant (surface resistivity or surface conductivity=1/surface resistivity) between the determined AC impedance (by EIS technique) and the orthogonal displacement (by the optical interferometry techniques) was obtained. Consequently the surface resistivity (ρ) and surface conductivity (σ) of the aluminium samples in solutions were obtained. Also, electrical resistivity values (ρ) from other source were used for comparison sake with the calculated values of this investigation. This study revealed that the measured values of the resistivity for the anodised aluminium samples were 2.8×10⁹, 7×10¹², 2.5×10¹³, and 1.4×10¹²  Ω cm in 1.0%, 1.5%, 2.0%, and 2.5% H₂SO₄ solutions, respectively. In fact, the determined value range of the resistivity is in a good agreement with the one found in literature for the aluminium oxide, 85% Al₂O₃ (5×10¹⁰ Ω cm in air at temperature 30 °C), 96% Al₂O₃ (1×10¹⁴  Ω cm in air at temperature 30 °C), and 99.7% Al₂O₃ (>1×10¹⁴ Ω cm in air at temperature 30 °C).