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.     

Spray pyrolysis deposition of Cu–Zn–In–S solid-solution thin films with tunable compositions and band gaps

Cu–Zn–In–S solid solution thin films with tunable compositions and band gaps were deposited on glass substrates using a chemical spray pyrolysis approach. XRD results reveal the cubic-structured Cu–Zn–In–S films without detectable impurities. The successive shift of XRD patterns toward high-angle side of ZnS with increasing ZnS molar fraction in products proves a formation of Cu–Zn–In–S solid solutions. SEM images and EDAX analyses demonstrate homogeneous surface morphologies and adjustable compositions of Cu–Zn–In–S films, which results in film band gaps broadly tunable from 1.54 eV to 3.61 eV. These sprayed Cu–Zn–In–S solid solution thin films may find potential uses in photovoltaics and photocatalysis.     

Effect of Isothermal Aging on the Long-Term Reliability of Fine-Pitch Sn–Ag–Cu and Sn–Ag Solder Interconnects With and Without Board-Side Ni Surface Finish

The combined effects on long-term reliability of isothermal aging and chemically balanced or unbalanced surface finish have been investigated for fine-pitch ball grid array packages with Sn–3.0Ag–0.5Cu (SAC305) (wt.%) and Sn–3.5Ag (SnAg) (wt.%) solder ball interconnects. Two different printed circuit board surface finishes were selected to compare the effects of chemically balanced and unbalanced structure interconnects with and without board-side Ni surface finish. NiAu/solder/Cu and NiAu/solder/NiAu interconnects were isothermally aged and thermally cycled to evaluate long-term thermal fatigue reliability. Weibull plots of the combined effects of each aging condition and each surface finish revealed lifetime for NiAu/SAC305/Cu was reduced by approximately 40% by aging at 150°C; less degradation was observed for NiAu/SAC305/NiAu. Further reduction of characteristic life-cycle number was observed for NiAu/SnAg/NiAu joints. Microstructure was studied, focusing on its evolution near the board and package-side interfaces. Different mechanisms of aging were apparent under the different joint configurations. Their effects on the fatigue life of solder joints are discussed.     

Synthesis and characterization of the as-deposited Cd1 ? x Pb x S thin films prepared by spray pyrolysis technique

Cd_{1 ? x} Pb _x S thin films were prepared by spray pyrolysis technique onto glass substrate at 300°C temperatures. The prepared films were characterized elemental, structural and optical properties by energy dispersive X-ray, scanning electron microscopy, X-ray diffraction and UV-VIS spectrophotometer. Energy dispersive X-ray confirmed the presence of Cd, S and Pb in the films. SEM images show that the deposition covered the substrate well uniformly and incorporation of Pb. Crystal structure was found hexagonal and the estimated grain size was lies in between 9 to 49 nm. The optical band gap was decreased from 2.43 to 2.07 eV.     

Phase transformation kinetics and optical properties of Ga–Se–Sb phase-change thin films

Phase transformation kinetics in Ga₂₅Se_75?xSb_x glasses have been determined by non-isothermal differential scanning calorimetric measurements at heating rates of 5, 10, 15, 20 and 25 K/min. The values of glass transition (T_g) and crystallization temperature (T_c) are found to be composition and heating rate dependent. The activation energy of crystallization and glass transition have been determined from the dependence of T_c and T_g on the heating rate. Thin films of Ga₂₅Se_75?xSb_x glasses have been prepared by vacuum evaporation technique with thickness 400 nm. These thin films were crystallized by thermal annealing and laser-irradiation. The phase change phenomena have been studied by measuring optical absorption of as-prepared and crystallized thin films in the wave length region 400–900 nm. The optical absorption data indicate that the absorption mechanism is non-direct transition. Optical band gap values decrease with increase in Sb contents in Ga–Se as well as with increase in annealing temperature and laser-irradiation time. The optical band gap is shifted due to crystallization by annealing/laser-irradiation. As the phase of the films changes from amorphous to crystalline, a non sharp change of the optical band gap is observed. This gradual decrease in optical band gap was explained to be a result of an amorphous–crystalline phase transformation.     

Observation of Meyer–Neldel rule in CdS thin films

A study of electrical transport in CdS thin films is reported. We have observed, for the first time, that CdS thin film conductivity obeys the Meyer–Neldel rule (MNR). This was deduced from linking the conductivity pre-exponential factor to the activation energy variation. CdS films were deposited by chemical bath deposition at different solution temperatures in order to vary the electrical activation energy of the films. A correlation between the MNR rule and the disorder in the film network is highlighted. The multi-trapping process in the band tail-localized states governs the conductivity in CdS films. This explains the MNR observation in CdS films. The variation of the electrical conductivity pre-exponential factor and activation energy are correlated to the disorder in the film network; this was explained in terms of polaron formation and phonon–electron coupling with disorder.     

Composition effect on the structure and optical parameters of Ge–Se–Te thin films

The present work reported the influence of Ge content variation on the optical properties of Ge_xSe₅₀Te_50-x (x=0, 5, 15, 20, 35 at%). Vacuum thermal evaporation technique was employed to prepare amorphous Ge_xSe₅₀Te_50−x thin films. The stoichiometry of the chemical composition was checked by energy dispersive X-ray spectroscopy (EDX), whereas the thin films structure was determined by an X-ray diffraction and a scanning electron microscope (SEM). The optical absorption measurements were performed at room temperature in the wavelength range of 200–900 nm. Many optical constants were calculated for the studied thin films utilizing the optical absorption data. It was observed that the optical absorption mechanism follows the rule of the allowed direct transition. The optical band gap was found to increase from 2.31 to 2.60 eV as the Ge content increases from 0 to 35 at%. This result was explained in terms of the chemical bond approach.     

Microwave properties and applications of Y–Ba–Cu–O thin films grown on various substrates

Microwave properties of YBa₂Cu₃O_7-δ (YBCO) films grown on (100) LaAlO₃ (LAO), (110) NdGaO₃ (NGO) and (001) SrLaAlO₄ (SLAO) substrates were studied in the form of a microstrip ring resonator at temperatures above 20 K. The YBCO resonator on a SLAO substrate showed microwave properties better than or comparable to other YBCO resonators on LAO substrates. For the YBCO resonators on LAO and SLAO substrates, both Q_U and f₀ appeared to decrease as the temperature was raised. Meanwhile the resonator on a NGO substrate showed different behaviors with Q_U showing a peak at ∼70 K, which are attributed to the unique temperature dependence of the loss tangent of the NGO substrate. An X-band oscillator with a YBCO ring resonator coupled to the circuit was prepared and its properties were investigated at low temperatures. The frequency of the oscillator signal appeared to change from 7.925 GHz at 30 K to 7.878 GHz at 77 K, which was mostly attributed to the change in f₀ of the YBCO ring resonator. The signal power appeared to be more than 4.5 mW at 30 K and 2.1 mW at 77 K, respectively. At 55 K, the frequency of the oscillator signal was 7.917 GHz with the 3 dB-linewidth of 450 Hz.     

Electrical and optical properties of very thin gold films †

The electrical and optical properties of discontinuous and semi-continuous gold films evaporated on to dielectric substrates in a high vacuum have been measured. The electrical properties of the films were characterized by DC conductivity and by the temperature coefficient of resistance: the reflectance and transmittance at near-infrared wavelengths were the optical properties considered. Special attention was given to the films in the vicinity of the percolation threshold.     

Post-annealing effects on structural and magnetic properties of Mn–N codoped ZnO thin films

The sputtered ZnO:Mn thin films were implanted with nitrogen ions (N⁺) and subsequently annealed at different temperatures up to 800 °C in N₂ atmosphere. The structural and magnetic properties of the samples were systematically investigated. Both x-ray diffraction and Raman analyses reveal that all the films are of the wurtzite structure of ZnO with no distinct evidence of secondary phases. X-ray photoelectron spectroscopy studies indicate that both Mn²⁺ and N³⁻ ions were incorporated into ZnO lattice successfully. While the films without nitrogen ions show paramagnetic behavior, ferromagnetism with clear hysteresis at 300 K is observed in Mn–N codoped ZnO films. Most importantly, we also found that the magnetic behavior of the codoped ZnO is very sensitive to the annealing temperature due to its effect on the activation of nitrogen ions. The strongest ferromagnetism is obtained in the films with the highest amount of nitrogen ions acceptors. Our results support the predication that the ferromagnetic ZnO:Mn²⁺ should be more stable of a hole-rich environment by theory.     

Implication of molecular orientation on charge transport and gas sensing characteristics of cobalt–phthalocyanine thin films

Charge transport and gas sensing characteristics of cobalt phthalocyanine films deposited along (ATB) and perpendicular (PTB) to the natural twin boundaries of (0 0 1) LaAlO₃ substrate have been investigated. The charge carrier mobility of ATB films (∼5 cm² V⁻¹ s⁻¹) is five orders of magnitude higher compared to that of PTB films (∼7 × 10⁻⁵ cm² V⁻¹ s⁻¹), suggesting that twin boundaries acts like a template for ordering of molecules. The ATB films on exposure to ammonia showed a reversible increase of resistance, with fast response and recovery. In contrast PTB films showed same sensitivity, but exhibits base resistance drift along with sluggish response.     

Thickness dependence of microwave surface resistance and critical current density in Ag–YBa2Cu3O7−x thin films

Microwave surface resistance and critical current density are measured in Ag-doped YBa₂Cu₃O_7−x thin films as a function of thickness of the film. The microwave surface resistance decreases monotonically as the thickness of the film is increased to an optimum thickness of 3000 Å. Beyond this optimum thickness the microstructure of the film deteriorates and the surface resistance increases as the thickness is further increased. Critical current density also increases as the thickness of the film is increased to the optimum thickness. The decrease in the value of surface resistance and an enhancement of J_c up to optimum thickness has been explained in terms of defects formed in the films during growth.     

Microstructure and magnetic properties of In1−xCrxN thin films

Microstructure and magnetic properties of In_1−xCr_xN thin films grown on GaN-on-sapphire templates by molecular beam epitaxy are investigated. Optimized growth conditions are identified for the In_1−xCr_xN thin films at reduced growth temperature. The In_1−xCr_xN thin films on the top of the InGaN buffer layers exhibit high crystalline-quality. The magnetic properties of In_1−xCr_xN thin films show a ferromagnetic behavior even at room temperature.     

Characterization of ZrTiO4 thin films prepared by sol–gel method

The electrical properties, memory switching behavior, and microstructures of ZrTiO₄ thin films prepared by sol–gel method at different annealing temperatures were investigated. All films exhibited ZrTiO₄ (111) and (101) orientations perpendicular to the substrate surface, and the grain size increased with increasing annealing temperature. A low leakage current density of 1.47×10^?6 A/cm² was obtained for the prepared films. The I–V characteristics of ZrTiO₄ capacitors can be explained in terms of ohmic conduction in the low electric field region and Schottky emission in the high electric field region. An on/off ratio of 10² was measured in our glass/ITO/ZrTiO₄/Pt structure with an annealing temperature of 600 °C. Considering the primary memory switching behavior of ZrTiO₄, ReRAM based on ZrTiO₄ shows promise for future nonvolatile memory applications.     

Microstructure and electrical properties of nitrogen doped 3C–SiC thin films deposited using methyltrichlorosilane

The growth, microstructure and electrical properties of in-situ nitrogen doped 3C–SiC (111) thin films for sensor applications are presented in this paper. These thin films are deposited at a pressure of 2.5 mbar and temperature of 1040 °C on thermally oxidized Si (100) substrates from methyltrichlorosilane (MTS) precursor using a hot wall vertical low pressure chemical vapor deposition (LPCVD) reactor. Ammonia (NH₃) is used as the nitrogen doping gas. The sensor response depends on chemical composition, structure, morphology and operating temperature. The above properties are investigated for all in situ nitrogen doped (0, 9, 17 and 30 at% of nitrogen) 3C–SiC thin films using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and four probe method. The XRD patterns of the 3C–SiC thin films show a decrease in the crystallinity and intensity of the peak with increase in dopant concentration from 0 to 17 at%. AFM investigations show an improvement in the grain size of the nitrogen doped 3C–SiC thin films with increase in nitrogen concentration from 0 to 17 at%. The sheet resistance of nitrogen doped 3C–SiC thin films is measured by the four probe technique and it is found to decrease with increase in temperature in the range of 40–550 °C. The resistivity and average temperature coefficient of resistance (TCR) of doped 3C–SiC thin film deposited with 17 at% of nitrogen concentration are found to be 0.14 Ω cm and −103 ppm/°C, respectively and this can be used as a sensing material for high temperature applications.     

Effect of solder resist dissolution on the joint reliability of ENIG surface and Sn–Ag–Cu solder

The electroless nickel immersion gold (ENIG) process results in surface defects, such as pinholes and black pads, which weaken the solder joint and eventually degrade the reliability of the PCB. Contamination of the plating solutions, including dissolution of the solder resist (SR), can be a cause of the pinholes and black pads. This study examined the effects of SR dissolution on the solder joint reliability and electroless Ni plating properties. Electroless Ni plating was performed by adding 1 to 10 ppm hardener (melamine) to the fresh Ni solution. Many black pads were observed in the 7 and 10 ppm hardener-added surfaces. In addition, the content of P was highest when 7 and 10 ppm hardener was added. The ball shear tests were carried out to confirm the joint reliability between the ENIG surface with hardener-added and the Sn-3.0Ag-0.5Cu solder (SAC 305). The ball shear strength decreased with increasing dissolution of the hardener. In particular, the shear strength was the lowest at 7 and 10 ppm hardener addition. In addition, the failure mode of the solder joint was changed from ductile to brittle mode with increasing hardener addition. That is, as the hardener additive increases, intermetallic compound (IMC) phases were changed from (Cu,Ni)₆Sn₅ to (Cu,Ni)₃Sn₄ and Cu₆Sn₅ (brittle structure).     

Optical and electrical properties of nickel oxide thin films synthesized by sol–gel spin coating

Nickel oxide thin films were prepared by the sol–gel technique combined with spin coating onto glass substrates. The as-deposited films were pre-heated at 275 °C for 15 min and then annealed in air at different temperatures. The effects of the annealing temperature on the structural and optical properties of the films are studied. The results show that 600 °C is the optimum annealing temperature for preparation of NiO films with p-type conductivity and high optical transparency. Then, by using these optimized deposition parameters, NiO thin films of various thicknesses were deposited at the same experimental conditions and annealed under different atmospheres. Surface morphology of the films was investigated by atomic force microscopy. The surface morphology of the films varies with the annealing atmosphere. Optical transmission was studied by UV–vis spectrophotometer. The transmittance of films decreased as the thickness of films increased. The electrical resistivity, obtained by four-point probe measurements, was improved when NiO layers were annealed in N₂ atmosphere at 600 °C.     

Optical and electrochemical gas sensing properties of yttrium–silver co-doped lithium iron phosphate thin films

The new sensing material, LiFe_0.995Y_0.0025Ag_0.0025PO₄ was synthesized using hydro-thermal methods, and characterized by X-ray diffraction, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The as prepared products were subsequently utilized in a self assembled optical waveguide gases testing apparatus and a WS-30A electro-chemical gas sensing apparatus for xylene detection. A glass optical waveguide gas sensor was fabricated by spin-coating a LiFe_0.995Y_0.0025Ag_0.0025PO₄ thin film on the surface of single-mode tin-diffused glass Optical Waveguide. The sensing elements for electro-chemical gas sensor were made by dip-coating a LiFe_0.995Y_0.0025Ag_0.0025PO₄ thin film on the surface of an alumina ceramic tube, assembled with platinum wire. The experimental results indicated that, at room temperature, LiFe_0.995Y_0.0025Ag_0.0025PO₄ thin film/tin-diffused optical waveguide sensing element exhibited higher response to xylene in the range of 0.1–100 ppm; at an optimum operating temperature (300 °C), the response (S_r) of LiFe_0.995Y_0.0025Ag_0.0025PO₄ to 100 ppm of xylene was 5.29, as measured by the WS-30A electro-chemical gases sensing apparatus.