Influence of Pb doping on the structural,morphological and optical properties of sol–gel ZnO thin films

In this work, undoped and lead (Pb)-doped ZnO thin films were deposited on glass substrate using the sol–gel dip-coating process. The effects of different Pb doping concentrations on the structural, morphological, optical, electrical and photoluminescence properties of such films were investigated by X-ray diffraction (XRD), energy-dispersive X-rays (EDS), atomic force microscopy (AFM), UV–vis–NIR spectrophotometry, Hall effect measurement and Photoluminescence (PL) spectroscopy. XRD patterns of the synthesized films exhibited hexagonal wurtzite crystal structure with a c-axis preferred (002) orientation. AFM images showed that film morphology and surface roughness were influenced by the Pb doping level. Incorporation of Pb was confirmed from elemental analysis using EDS. The UV–vis–NIR spectroscopy characterizations demonstrated that all the films were highly transparent with average visible transmission values ranging from 75% to 85%. Electrical measurement shows that carrier concentration and resistivity are dependent on Pb content. Room temperature PL spectra clearly indicated a great dependence of the UV, green and red emissions on the Pb concentration. In particular, the red emission at 2 eV is quenched after introduction of Pb atoms.     

Effect of Chromium Doping on the Thermoelectric Properties of Bi2Te3: Cr x Bi2Te3 and Cr x Bi2−x Te3

The thermoelectric (TE) properties of Bi₂Te₃ compounds intercalated and substituted with Cr, namely Cr _x Bi₂Te₃ and Cr _x Bi_2?x Te₃, respectively, have been investigated to study the influence of chromium on the TE properties of Bi₂Te₃. The Seebeck coefficients were found to be positive for all the samples in the temperature range between 300 K and 550 K. Although no effective enhancement of the Seebeck coefficient was observed, doping with Cr by means of either substitution or intercalation clearly not only improved the electrical conductivity but also lowered the thermal conductivity of Bi₂Te₃. As a result of the improvement, the figure of merit ZT is increased up to 0.8 and 0.65 at 300 K for 1% intercalated and 1% substituted Bi₂Te₃, respectively.     

Influence of copper concentration on the opto-structural,morphological and electrical properties of novel MoSb2−xCuxSe2 thin films

In this work, MoSb_2−xCu_xSe₂ nanocrystalline thin films obtained for different copper concentrations (0.1, 0.2 and 0.3 M) on glass substrates by simple chemical bath deposition (CBD) method at room temperature. X-ray diffraction (XRD) patterns revealed the incorporation of copper content by the conversion of orthorhombic Sb₂Se₃ into orthorhombic Cu₃SbSe₃ with shift to higher angles. Average crystallite was found to be 24, 36 and 39 nm for the deposited films. FESEM analysis indicates that morphological transition from spherical grains with cylindrical nanorods to porous nanofibers for 0.3 M and HRTEM confirms the FESEM results with an average grain size of 200 nm for 0.1 M Cu concentration. EDS analysis confirmed the formation of MoSb_2−xCu_xSe₂ thin films. Current–Voltage (I–V) measurements clearly depicted the ohmic nature of the material in the entire region. Thickness of the films was found to be increased with increase in copper content. The band gap energy (E_g) of the film is in the range of 1.644–3.757 eV.     

Influence of substrate type on the structural,optical and electrical properties of CdxZn1−xS MSM thin films prepared by Spray Pyrolysis method

0.25 μm Cd_xZn_1−xS thin films were deposited on Si and glass substrates by using a chemical Spray Pyrolysis technique (CSP). Measurements of the absorption spectrum of the film were carried out. The values of band gaps (E_g) are calculated from the absorption spectrum. X-ray diffraction (XRD) of the Cd_xZn_1−xS thin films on Si and glass substrates was carried out. The full width at half-maximum (FWHM)) of diffraction peak was calculated to be about 0.640, which showed that it is a polycrystalline thin film. A Cd_xZn_1−xS Metal–Semiconductor–Metal (MSM) photodetector with nickel (Ni) contact electrodes was then fabricated. The electrical property of the Ni/Cd_xZn_1−xS/Si and Ni/Cd_xZn_1−xS/glass detectors was investigated using the current–voltage (I–V) measurements. The barrier heights ϕ_Β of Ni/Cd_xZn_1−xS/Ni MSM on Si and glass substrates were 0.551 eV and 0.593 eV, respectively with an applied bias voltage of 3 V.     

Structural and optical properties of hexagonal MgxZn1−xO thin films

High-quality epitaxial magnesium zinc oxide (Mg_xZn_1-xO) alloy thin films were grown on sapphire (α-Al₂O₃ (0001)) substrates using pulsed laser deposition. The structural and optical properties of these hexagonal films were determined using transmission electron microscopy (TEM), x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), absorption, and photoluminescence measurements. XRD and TEM data reveal that magnesium zinc oxide alloy films, grown by domain matching epitaxy, exhibited the following relationships: MgZnO[0001] ∥ α-Al₂O₃ [0001] and MgZnO[01 0] ∥ α-Al₂O₃ [2 0]. RBS data demonstrate that a maximum magnesium content of x=0.34 can be obtained in hexagonal Zn_xMg_1-xO thin films. This value is significantly higher than the thermodynamic limitation of x=0.04. The absorption spectra of magnesium zinc oxide alloy films obtained at room temperature demonstrate significant excitonic behavior. The exciton binding energies have been extracted from the absorption data. Values of the exciton bandgap as a function of magnesium content were determined by fitting the bandgap energies using polynomial fitting. The Zn_xMg_1−xO alloy thin films demonstrate bright room-temperature luminescence and significant excitonic behavior. A shift in the excitonic emission peak as a function of magnesium content was observed.     

Investigations on the structural and optical properties of Li,N and (Li,N) co-doped ZnO thin films prepared by sol–gel technique

Pure and doped zinc oxide thin films have been deposited on sapphire substrates by using the sol–gel method and spin coating technique. The X-ray diffraction pattern showed that the deposited films exhibit hexagonal zinc oxide structure. Room temperature photoluminescence measurements show the presence of two emission bands. The predominant near band edge ultraviolet emission is at 3.28 eV and a suppressed broad band of deep level emission in the range of 2.1–2.5 eV. The incorporation of nitrogen is indicative of p-type behavior as observed from X-ray photoelectron spectrum of nitrogen in the doped samples. The p-type conduction of Li, N:ZnO may be attributed to the formation of a LiZn–N complex acceptor.     

Sigmoid-growth curve of lattice-constant against annealing-temperature of Cd1−xZnxTe thin films and its structural,optical and morphological characteristics

Stacked CdTe/Zn/CdTe layers were deposited on glass substrates. The vacuum-evaporated thin films were subsequently annealed in vacuum ambience at various temperatures. Change in lattice-constant of major Cd_1−xZn_xTe planes against temperature was plotted from the XRD results. The graphs followed sigmoid-growth model and were regressed well by standard Boltzmann and Logistic functions. Lattice-constant varied maximum in between 375–400 °C and 425–450 °C, giving two separate growth trends. Optical studies suggested that presence of charge impurities and defects reduced the transmittance and band-gap values of the samples. Such reduction occurred, despite of greater formation of Cd_1−xZn_xTe. Decreasing granularity was however associated with increasing band-gap for samples annealed at 425 and 450 °C. SEM micrographs showed that granularity decreased significantly for samples annealed at higher temperatures. EDX results were further used to co-relate the compositional characteristics with structural and optical features.     

Influence of substrate temperature on the deposition and structural properties of μc-Si: H thin films fabricated with VHF-PECVD

With in situ optical emission spectroscopy (OES) diagnosis on VHF-generated H₂+SiH₄ plasmas, and with the measurements of deposition rate and structure of μc-Si: H thin films fabricated with VHF-PECVD technique at different substracte temperature, influence of substrate temperature on the deposition of μc-Si: H thin film and on its structural properties have been investigated. The results show that with the increase of substrate temperature, the crystalline volume fraction Xc and average grain size d are enhanced monotonously, but the deposition rate increases firstly and then decreases. The optimized substrate temperature for (μc-Si: H thin films deposition under our current growth system is about 210 °C, at which deposition rate 0.8 nm/s of μc-Si: H thin film with Xc?60% and d?9 nm can be obtained.     

Influence of substrate temperature on the deposition and structural properties of μc-Si:H thin films fabricated with VHF-PECVD

Inordertoimprovetheefficiency,stabilityofsilicon basesolarcells,andtoloweritscosts,tandemstruc ture[1]andlight traptechnique[2]havebeenwidelyem ployed.Recently,moreandmoreattentionshavebeenpaidtomicrocrystallinesiliconμc Si:H4filmdeposited atlowtemperaturebecauseofitspromisingapplication tostablehighefficiencysolarcells,andsomeremarkableprogresseshavebeenmadeinμc Si:Hthinfilmdeposi tionanditsapplicationinsolarcells[3 7].Ingeneral,VHF PECVDtechnique,basedonVHF generatedplasma,ismorec…     

Effect of Co2+ ions on structural,morphological and optical properties of ZnO nanoparticles synthesized by sol–gel auto combustion method

Undoped and Co²⁺ doped ZnO nanoparticles have been successfully synthesized by sol–gel auto combustion method. The ratio of metal nitrates to citric acid was taken at 1:1.11. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared and Uv–visible spectroscopy techniques. The X-ray powder diffraction analysis revealed the formation of single phase having hexagonal wurtzite structure. The lattice constant ‘a’ increases while ‘c’ decreases as Co²⁺ concentration ‘x’ increases. The average crystallite size obtained from XRD data is in the range of 19–15 nm. The X-ray density, atomic packing factor, strain, surface area to volume ratio, etc was obtained using XRD data. SEM analysis showed that the prepared nanoparticles are in nano regime, nearly spherical and loosely agglomerates. EDAX analysis showed that composition obtained is near stoichiometries. In order to understand functional group and vibrational frequency band position of synthesized nanoparticles FTIR technique was used. FTIR analysis results observed that vibrational frequency band position of Zn–O shifted to higher frequency band with Co²⁺ ion increasing host semiconductor nanoparticles. Uv–visible absorption spectra showed that absorption edge shifted to higher wavelength with increasing Co²⁺ concentration while corresponding energy band gap of semiconductor nanoparticles decreases with increasing Co²⁺ concentration.     

Effect of bath temperature on the properties of CuIn_χGa_(1-χ)Se_2 thin films grown by the electrodeposition technique

Electrodeposition is a promising and low cost method to synthesize CuIn_xGa_(1-x)Se_2(CIGS)thin films as an absorber layer for solar cells.The effect of bath temperature on the properties of CIGS thin films was investigated in this paper.CIGS films of 1μm thickness were electrodeposited potentiostatically from aqueous solution,containing trisodium citrate as a complexing agent,on Mo/glass substrate under a voltage of-0.75 V,and bath temperatures were varied from 20 to 60℃.The effects of bath temperature ...     

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.     

Effect of compositional disorder on the optical properties of Cd1−xZnxTe

Time-resolved as well as time-integrated luminescence of a bulk grown undoped Cd_0.12Zn_0.88Te crystal is measured to investigate the effect of compositional disorder on the recombination dynamics. The temporal behavior of the neutral-donor-bound exciton emission is well expressed by a simple exponential rise and decay. However, non-exponential rise and decay are observed for the acceptor-bound-exciton emission. It is shown that by introducing an intermediate state for the transition, the temporal behavior, especially the rising edge, of the acceptor bound exciton emission can well be described by a rate equation model.     

Effect of Se Substitution on Structural and Electrical Transport Properties of Bi0.4Sb1.6Se3x Te3(1−x) Hexagonal Rods

In the current study, novel hexagonal rods based on Bi_0.4Sb_1.6Te₃ ingots dispersed with x amount of Se (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in the form Bi_0.4Sb_1.6Se_3x Te_3(1?x) were synthesized via a standard solid-state microwave route. The morphologies of these rods were explored using field-emission scanning electron microscopy (FESEM). The crystal structure of the powders was examined by x-ray diffraction (XRD) analysis, which showed that powders of the 0.0 ≤ x ≤ 0.8 samples could be indexed to the rhombohedral phase, whereas the sample with x = 1.0 had an orthorhombic phase structure. The influence of variations in the Se content on the thermoelectric properties was studied in the temperature range from 300 K to 523 K. Alloying of Se into Bi_0.4Sb_1.6Te₃ effectively caused a decrease in the hole concentration and, thus, a decrease in the electrical conductivity and an increase in the Seebeck coefficient. The maximal power factor measured in the present work was 7.47 mW/mK² at 373 K for the x = 0.8 sample.     

Effect of sodium doping on graded Cu(In1−xGax)Se2 thin films prepared by chemical spray pyrolysis

In the present work we have studied the effect of Na on the properties of graded Cu(In_1−xGa_x)Se₂ (CIGS) layer. Graded CIGS structures were prepared by chemical spray pyrolysis at a substrate temperature of 350 °C on soda lime glass. Sodium chloride is used as a dopant along with metal (Cu/In/Ga) chlorides and n, n-dimethyl selenourea precursors. The addition of Na exhibited better crystallinity with chalcopyrite phase and an improvement in preferential orientation along the (112) plane. Energy dispersive analysis of X-rays (line/point mapping) revealed a graded nature of the film and percentage incorporation of Na (0.86 at%). Raman studies showed that the film without sodium doping consists of mixed phase of chalcopyrite and CuAu ordering. Influence of sodium showed a remarkable decrease in electrical resistivity (0.49–0.087 Ω cm) as well as an increase in carrier concentration (3.0×10¹⁸–2.5×10¹⁹ cm⁻³) compared to the un-doped films. As carrier concentration increased after sodium doping, the band gap shifted from 1.32 eV to 1.20 eV. Activation energies for un-doped and Na doped films from modified Arrhenius plot were calculated to be 0.49 eV and 0.20 eV, respectively. Extremely short carrier lifetimes in the CIGS thin films were measured by a novel, non-destructive, noncontact method (transmission modulated photoconductive decay). Minority carrier lifetimes of graded CIGS layers without and with external Na doping are found to be 3.0 and 5.6 ns, respectively.     

Effect of Fe doping on structural and magnetic properties of La2/3Ca1/3Mn1−yFeyO3 (y=0–0.03) thin films

We have characterized the magnetic and structural properties of pure and ⁵⁷Fe-doped La_2/3Ca_1/3MnO₃ thin films and targets, substituted with 1% and 3% of ⁵⁷Fe on the Mn site. The films were prepared via high O₂-pressure (500 mTorr) by DC magnetron sputtering on (1 0 0) SrTiO₃ and (1 0 0) LaAlO₃ single-crystal substrates. Mössbauer spectra measured at room temperature confirm the presence of Fe³⁺ with octahedral coordination, thus indicating that Fe is incorporated into the structure by substituting Mn. Structural analysis by X-ray diffraction (XRD) shows that the films are single phase and c-axis oriented and that the Fe doping gives rise to a relaxation of the epitaxial strain. Interestingly, the Curie temperature and the magnetoresistance (MR) show a non-monotonic behavior with Fe doping. This indicates that initially the strain relaxation induced by the Fe doping is more important than the reduction of ferromagnetic coupling due to the Fe incorporation.     

Growth of high quality YbBa2Cu3O7−δ thin films by pulsed laser deposition

YbBa₂Cu₃O_7−δ (Yb-123) films are deposited for the first time using Pulsed Laser Deposition (PLD) method at three different substrate temperatures, viz. 675°C, 700°C and 725°C. Films are characterized using XRD, dc electrical resistivity, critical current density (J_c) and microstructural study by Atomic Force Microscopy (AFM) techniques. It is found that 700°C is the optimum growth temperature for growing high quality Yb-123 films. The best T_c and J_c values obtained at optimum growth conditions are 88 K and 2.6×10⁶ A cm⁻² at 77 K, respectively. AFM photographs provide evidence in confirming the relation between growth temperature and superconducting properties.     

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.     

Structural and optical properties of (Al,K)-co-doped ZnO thin films deposited by a sol–gel technique

Thin films of Al-doped ZnO (AZO) and (Al, K)-co-doped ZnO (AKZO) were synthesized by sol–gel spin coating and their structural and optical properties were investigated. All the films had a preferential orientation in which the c-axis was perpendicular to the substrate. The optical bandgap increased after Al doping, but decreased after K doping at a given Al doping concentration. UV emission and a broad visible emission band were observed in photoluminescence (PL) spectra. The intensity of both emission bands decreased after Al and K co-doping. PL excitation (PLE) spectra of the blue emission band indicate that the initial state is possibly the same for all the samples and a similar case occurs for the orange–red emission band. The green emission can be attributed to electronic transitions involving oxygen vacancies. A possible process for the orange–red emission of the thin films is radiative recombination of an electron trapped in a zinc interstitial defect with a hole deeply trapped in interstitial oxygen.