Effect of the film thickness on the optical constants and dispersion parameters of chalcogenide Ge20Se70Ag10 thin film

Chalcogenide thin films of Ge₂₀Se₇₀Ag₁₀ of thicknesses 150, 300 and 450 nm are prepared by a thermal evaporation technique. The crystalline phases of the deposited film are identified by X-ray diffraction. The transmittance and reflectance of the films are measured in the wavelength range 200–2500 nm. The optical band gap decreases while the width of the localized states tail increases with increasing film thickness. Variation of refractive index and extinction coefficient with the film thickness is studied to analyze the optical efficiency of these films. Application of the single oscillator model to the films reveals that the oscillator energy decreases while the dispersion energy increases with increasing thickness. The variation of the optical constants suggests that the thickness change is a good choice to control the optical properties of Ge₂₀Se₇₀Ag₁₀ film.     

Investigation of strontium tantalate thin films for high-k gate dielectric applications

Strontium tantalate (STO) films were grown by liquid-delivery (LD) metalorganic chemical vapor deposition (MOCVD) using Sr[Ta(OEt)₅(OC₂H₄OMe)]₂ as precursor. The deposition of the films was investigated in dependence on process conditions, such as substrate temperature, pressure, and concentration of the precursor. The growth rate varied from 4 to 300 nm/h and the highest rates were observed at the higher process temperature, pressure, and concentration of the precursor. The films were annealed at temperatures ranging from 600 to 1000 °C. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and ellipsometry indicated that the as-deposited and the annealed films were uniform and amorphous and a thin (>2 nm) SiO₂ interlayer was found. Crystallization took place at temperatures of about 1000 °C. Annealing at moderate temperatures was found to improve the electrical characteristics despite different film thickness (effective dielectric constant up to 40, the leakage current up to 6×10⁻⁸ A/cm², and lowest midgap density value of 8×10¹⁰ eV⁻¹ cm⁻²) and did not change the uniformity of the STO films, while annealing at higher temperatures (1000 °C) created voids in the film and enhanced the SiO₂ interlayer thickness, which made the electrical properties worse. Thus, annealing temperatures of about 800 °C resulted in an optimum of the electrical properties of the STO films for gate dielectric applications.     

Thickness-dependent optoelectronic properties of CuCr0.93Mg0.07O2 thin films deposited by reactive magnetron sputtering

CuCr_0.93Mg_0.07O₂ thin films were successfully deposited by DC reactive magnetron sputtering at 1123 K from metallic targets. The influence of film thickness on the structural and optoelectronic properties of the films was investigated. X-ray diffraction (XRD) results revealed that all the films had a delafossite structure with no other phases. The optical and electrical properties were investigated by UV–VIS spectrophotometer and Hall measurement, respectively. It was found that the optoelectronic properties exhibited a thickness-dependent behavior. The optical band gap and the average transmittance of the films showed a monotonous decrease with respect to the increase in thickness. The average transmittance in the visible region decreased from 67% to 47% as the thickness increased from ~70 nm to ~280 nm. Simultaneously, the conductivity of the films fell from 1.40 S∙cm⁻¹ to 0.27 S∙cm⁻¹. According to Haacke's figure of merit (FOM), a film with a maximum FOM value of about 1.72×10⁻⁷ Ω⁻¹ can be achieved when the thickness is about 70 nm (σ≈ 1.40 S·cm⁻¹ and T_av. ≈67%).     

Evidence of interface dominated photovoltaic effect of Pt-sandwiched polycrystalline BiFeO3 thin film capacitors

Photovoltaic (PV) effects of Pt sandwiched polycrystalline BiFeO₃ (BFO) thin films deposited directly on Pt(111)/Ti/ SiO₂/Si(001) substrate at 550 °C by radio frequency magnetron sputtering are investigated under different BFO film thicknesses. It is found that both 300 and 450 nm thick BFO thin films do not exhibit obvious PV effects, which can be attributed to their large leakage current density. However, obvious PV effects are observed in the samples of 600 and 750 nm in thickness. It is found that not only the open circuit voltage but also the short circuit current density of the two samples decreases with the increasing annealing temperature on top Pt/BFO interfaces. The obtained PV results can be explained by the change of the interface state induced by the high temperature thermal treatment.     

厚度对TaN薄膜电性能的影响研究

采用直流反应磁控溅射法制备了TaN薄膜,研究了薄膜厚度对TaN薄膜微观结构及电性能的影响。结果表明,薄膜厚度对TaN薄膜的表面形貌和相结构都没有影响,但会显著影响TaN薄膜的电学性能。在87~424 nm的范围内,随着薄膜厚度的增大,所制TaN薄膜的电阻率从555×10–6.cm减小到285×10–6.cm,方阻从84/□减小到9/□,电阻温度系数(TCR)从–120×10–6/℃增加到+50×10–6/℃。可以通过调节薄膜的厚度调节TaN薄膜的电阻率和TCR。     

Growth of single unit-cell superconducting La2−xSrxCuO4 films

We have developed an approach to grow high quality ultra-thin films of La_2−xSr_xCuO₄ with molecular beam epitaxy, by adding a homoepitaxial buffer layer in order to minimize the degradation of the film structure at the interface. The advantage of this method is to enable a further reduction of the minimal thickness of a superconducting La_1.9Sr_0.1CuO₄ film. The main result of our work is that a single unit cell (only two copper oxide planes) grown on a SrLaAlO₄ substrate exhibits a superconducting transition at 12.5 K (zero resistance) and an in-plane magnetic penetration depth λ_ab(0)=535 nm.     

CuxS背接触层制备及在碲化镉薄膜太阳电池中应用研究

本文采用化学水浴法沉积CuxS薄膜,通过改变Cu元素比例研究其对碲化镉电池效率的影响。研究表明化学水浴法沉积的CuxS是非晶的,采用适当退火条件可以使其晶化,随着退火温度的提高,薄膜变得致密且结晶明显。CuxS薄膜厚度对电池性能有很大的影响,结果表明,随着CuxS薄膜厚度增加,电池性能先增加后减少。薄膜厚度为75nm时,CdS/CdTe电池性能最佳,达到了最高转化效率(η)为12.19%,填充因子(FF)为68.82%,开路电压(Voc)为820mV。     

Structural and the optical dispersion parameters of nano-CdTe thin film/flexible substrate

CdTe thin films of different thicknesses were deposited on polymer substrates for flexible optical devices applications. X-ray diffractogram of different thicknesses for CdTe films are measured and their patterns exhibit polycrystalline nature with a preferential orientation along the (111) plane. The optical constants of CdTe films were calculated based on the measured transmittance spectral data using Swanepoel's method in the wavelength range 400–2500 nm. The refractive index n and absorption index k were calculated and the refractive index exhibits a normal dispersion. The refractive index dispersion data followed the Wemple–DiDomenico model based on single oscillator. The oscillator dispersion parameters and the refractive index no. at zero photon energy were determined. The possible optical transition in these films is found to be allowed direct transition with energy gap increase from 1.46 to 1.60 eV with the increase in the film thickness. CdTe/flexible substrates are good candidates in optoelectronic devices     

Study on thermal solid-phase crystallization of amorphous ZnO thin films stacked on vanadium-doped ZnO films

Thermal solid-phase crystallization (SPC) of an amorphous ZnO film stacked on a vanadium-doped ZnO (VZO) film was investigated. ZnO films were deposited on 30-nm-thick amorphous VZO films on c-face sapphire substrates at room temperature by RF magnetron sputtering. Stacked film was subsequently calcined at 800 °C in a nitrogen atmosphere. ZnO film grew in an amorphous state up to about 150-nm thick on the amorphous VZO film, but self-orientation occurred in a thicker layer. Any secondary phase such as Zn₂VO₄ was not formed in the case of total film thickness (t_total) ≥100 nm. V concentration decreased by thermal diffusion of V through the ZnO layer from the VZO film, and thereby the formation of secondary phase was effectively avoided. The amorphous ZnO layer was crystallized from highly-aligned initial thin layer of VZO film when t_total ≤200 nm and crystal orientation of the stacked film was superior to single VZO film. However, the c-axis orientation was deteriorated drastically at t_total ≈400 nm due to SPC affected by the tilted regions existed in the as-deposited ZnO film. Therefore, it is suggested that careful selection of ZnO film thickness is necessary to obtain the high-quality ZnO films in this method.     

Morphological and electrical characterization of SixCryCzBv thin films

Si_xCr_yC_zB_v thin films with several compositions have been studied for integration of high precision resistors in 0.8 μm BICMOS technology. These resistors, integrated in the back-end of line, have the advantage to provide high level of integration and attractive electrical behavior in temperature, for analog devices. The film morphology and the structure have been investigated through transmission electron microscopy analysis and have been then related to the electrical properties on the base of the percolation theory. According to this theory, and in agreement with experimental results, negative thermal coefficient of resistance (TCR) has been obtained for samples with low Cr content, corresponding to a crystalline volume fraction below the percolation threshold.Samples with higher Cr content exhibit, instead, a variation of the TCR as a function of film thickness: negative TCR values are obtained for thickness lower than 5 nm, corresponding to a crystalline volume fraction below the percolation threshold; positive TCR are obtained for larger thickness, indicating the establishment of a continuous conductive path between the Cr rich grains. This property seems to be determinant in order to assure the possibility to obtain thin film resistors almost independent on the temperature.     

Effect of the deposition rate on the phase transition in silver telluride thin films

Silver telluride thin films of thickness 50 nm have been deposited at different deposition rates on glass substrates at room temperature and at a pressure of 2×10⁻⁵ mbar. The electrical resistivity was measured in the temperature range 300–430 K. The temperature dependence of the electrical resistance of Ag₂Te thin films shows structural phase transition and coexistence of low temperature monoclinic phase and high temperature cubic phase. The effect of deposition rate on the phase transition and the electrical resistivity of silver telluride thin films in relation to carrier concentration and mobility are discussed.     

Structural,surface morphology and optical properties of sputter-coated CaCu3Ti4O12 thin film: Influence of RF magnetron sputtering power

This study focusses on the investigation of RF power variations (100–300 W) effects on structural, morphological and optical properties of CaCu₃Ti₄O₁₂ thin film deposited on ITO/glass substrate in a non-reactive atmosphere (Ar). The increase of RF power from 100 W to 300 W led to evolution of (112), (022), (033), and (224) of CCTO XRD peaks. The results indicated that all the films were polycrystalline nature with cubic structure. The crystallite size increased from 20 nm to 25 nm with increasing RF power. FESEM revealed that the films deposited were uniform, porous with granular form, while the grain size increased from 30 to 50 nm. AFM analysis confirmed the increment in surface roughness from 1.6 to 2.3 nm with increasing film grain size. Besides, optical transmittance values decreased to minimum 70% with increasing RF power while optical energy bandgap increased from 3.20 eV to 3.44 eV. Therefore, favorable CCTO thin film properties can be possibly obtained for certain application by controlling RF magnetron sputtering power.     

Thickness Dependence Study of Electron Beam Evaporated LBMO Manganite Thin Films for Bolometer Applications

La_0.7Ba_0.3MnO₃ (LBMO) thin films with different thicknesses were deposited on Si substrates using an electron beam evaporation technique for bolometer applications. To evaluate the influence of the thickness on their structural, compositional, morphological, and electrical properties, the LBMO thin films were characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy, atomic force microscopy, and a four-probe method. XRD measurements showed that the crystal quality of the LBMO films improved with increasing thickness. The surface morphology revealed that the grain size and surface roughness of the films increased with increasing thickness. The resistivity increased with increasing thickness of the film. The temperature coefficient of resistance of the LBMO films decreased from 5.15%/K to 4.12%/K with increase of the film thickness from 20 nm to 100 nm.     

Optical and electrical characterization of the electron beam gun evaporated TiO2 film

We report measured evolutions of the optical band gap, refractive index and relative dielectric constant of TiO₂ films obtained by electron beam gun evaporation and annealed in an oxygen environment. A negative shift of the flat band voltage with increasing annealing temperatures, for any film thickness, is observed. A dramatic reduction of the leakage current by about four orders of magnitude to 5×10⁻⁶ A cm⁻² (at 1 MV cm⁻¹) after 700°C and 60 min annealing is found for films thinner than 15 nm. The basic carrier transport mechanisms at different ranges of applied voltage such as hopping, space charge limited current and Fowler–Nordheim is established. An equivalent SiO₂ thickness in order of 3.5 nm is demonstrated.     

Effects of silver substrates on the visible light photocatalytic activities of copper-doped titanium dioxide thin films

Novel copper-doped titanium dioxide (Cu-doped TiO₂) thin films on silver (Ag) substrates with different thicknesses were prepared by sol–gel and magnetron sputtering methods. The influences of the Ag substrate thickness on the morphology and performance of the films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV–visible spectroscopy, and photocatalytic degradation testing with methylene blue aqueous solution under visible light irradiation. The results indicated that Ag substrates with an optimal thickness of 30 nm not only maintained the tiny nanocrystals but also greatly improved dispersion of the nanoparticles on the surface of the nanofilms. Furthermore, during the calcination process, part of the Ag atoms diffused from the substrates into the Cu–TiO₂ films and substituted for the Cu ions to form Ag–TiO₂. A proper Ag substrate thickness (30 nm) greatly improved the photocatalytic properties of TiO₂ with photocatalytic efficiency, reaching approximately 86% in 300 minutes under visible light irradiation. However, an excess of Ag substrate not only led to the Cu ion separating out in the form of CuO but also resulted in the agglomeration of TiO₂ particles on the surface, which were detrimental to photocatalytic activities.     

The correlation of γ-irradiation,particle size and their effects on physical properties of AgInSe2 nanostructure thin films

In this work the effect of γ-irradiation on the optical and electrical properties of near stoichiometric AgInSe₂ nanostructure thin films have been characterized. The XRD pattern of ingot AgInSe₂ powder prepared by solid state reaction showed tetragonal polycrystalline single-phase structure. The thin films of thickness 75 nm were prepared by inert gas condensation (IGC) technique at using constant Ar flow and substrate temperature of 300 K.Thin films were exposed to annealing process at 473 K for 2 h in vacuum of 10⁻² Torr. The amorphous and tetragonal nanocrystalline structures were detected for as-deposited and annealed films respectively by grazing incident in-plane X-ray diffraction (GIIXD) technique. The structure and average particle size of annealed irradiated films by different γ-doses from 0 to 4 Mrad were determined using high resolution transmission electron microscope (HRTEM). Optical transmission, reflection and absorption spectra were studied for both annealed unirradiated and irradiated films. Two optical transitions for each annealed unirradiated and film exposed to γ-irradiation doses from 0 to 4 Mrad were observed. The evaluated E_g1 due to 1^st transition have decreased from 1.52 to 1.44 eV and E_g2 due to 2^nd transition have decreased from 2.83 to 2.30 eV as the particle size increased from 7.3 to 9.5 nm by raising the irradiation dose up to 1 Mrad. The behavior of d.c. electrical conductivity with temperature that measured under vacuum was examined for all films under investigation. The evaluated activation energies due to irradiation doses are ranging from 0.58 to 0.68 eV.     

Dielectric properties of Fe-doped BaxSr1−xTiO3 thin films on polycrystalline substrates at temperatures between −35 and +85 °C

Large-area Ba_xSr_1−xTiO₃ (BSTO-x) thin films, partially Fe-doped, have been grown by pulsed laser deposition (PLD) on technically relevant polycrystalline alumina based ceramics. The capacity (dielectric constant _r) and Q-factor of planar Pt/BTO:Fe/Pt capacitors were investigated within a temperature range from −35 to +85 °C. The applied DC-bias voltages were up to 10 V and the measurement frequency was 1 kHz.Although operating in the ferroelectric state below the Curie temperature, pure BaTiO₃ (BTO) thin films showed the smallest variation of _r within the temperature range from −35 to +85 °C compared to BSTO-0.6 and BSTO-0.8. The temperature dependence of _r below the Curie temperature (ferroelectric state) seems to be smaller than above the Curie temperature (paraelectric state) for the BSTO-x system. A homogeneous tunability of the capacity of about 60% was achieved for applied electrical DC voltages resulting in electrical field strengths between 0 and 5 V/μm within the whole temperature range. The Q-factor of 2 μm thick BTO films increases with increasing DC bias voltage. Furthermore, by Fe-doping of BTO films Q-factors could be increased by a factor of three up to about 70 compared to the not doped films. In addition, the temperature dependence of capacity is considerably influenced by Fe-doping.At a microwave frequency of 30 GHz high _r values of about 1500 were measured for large-area BSTO-0.45 films at room temperature deposited directly on microwave ceramic substrates. Low values of tanδ of about 0.003 were measured for the PLD-BSTO-0.45 films which corresponds to a Q-factor of more than 300. The results show the potential of ferroelectric BTO thin films for applications as tunable electronic devices in a wide temperature range.     

MOCVD of ferroelectric thin films

A low-pressure chemical vapor deposition system for growing ferroelectric thin PZT films has been developed. It consists of a dispensing and vaporizing system for up to four liquid metal precursors and a cold wall reactor, where the reactions are carried out at pressures below 1 Torr and at temperatures between 330 and 500°C. The thickness of the deposited films ranged from 10 nm to 1 μm. The investigated films in this report are lead-titanate, PbTiO₃, and lead-zirconate-titanate, Pb(Zr,Ti)O₃.     

Deposition of aluminum oxide-doped zinc oxide transparent nano-films on glass substrates for electrostatic discharge applications

Aluminum oxide-doped zinc oxide (ZnO:Al₂O₃) transparent thin films were deposited by DC magnetron sputtering on glass substrates; film thickness can be correlated with deposition time. The effect of ZnO:Al₂O₃ film thickness on electrical properties, ultraviolet (UV) transmission, surface morphology and structure, solvent resistance, and scratch hardness was investigated. The surface roughness and crystallite size of deposited films increased from 0.75 to 2.22 nm and from 14 to 57 nm, respectively, as the film thickness was increased from 18 to 112 nm. In contrast, the percent UV transmission (% T) of ZnO:Al₂O₃ deposited glass plates at a wavelength of 365 nm increased when the film thickness was decreased. The electrical properties of nano-film deposited glass plates such as electrical resistance, tribo-charge voltage, and decay time were in the range of electrostatic discharge (ESD) specifications. The ZnO:Al₂O₃ nano-film deposited glass substrate possessed good acetone and iso-propanol resistance as well as high scratch hardness. This work opens up the possibility of using the ZnO:Al₂O₃ transparent ultra-thin film on glass substrate in ESD applications based on their excellent properties in terms of the relatively thin and adjustable ZnO:Al₂O₃ film thickness needed.     

Investigation of the optical and structural properties of thermally evaporated cadmium sulphide thin films on polyethylene terephthalate substrate

Cadmium sulphide (CdS) thin films of different thicknesses ranging from 100 to 400 nm were prepared on polyethylene terephthalate (PET) substrates at room temperature by thermal evaporation technique in vacuum of about 3×10⁻⁵ Torr. The structural characterisation was carried out by X-ray diffraction (XRD). These studies confirm the proper phase formation of the cadmium sulphide structure. The root mean square (RMS) roughness of the films was measured using atomic-force microscopy. The root mean square roughness of the films increases as the film thickness increases. The energy gap of CdS on PET substrates was determined through the optical transmission method using an ultraviolet–visible spectrophotometer. The optical band gap values of CdS thin films slightly increase as the film thickness increases. The optical band gap energy was found to be in the range of 2.41–2.56 eV.