Electrical and optical properties of chemical solution deposited barium hafnate titanate thin films

We have investigated the electrical and optical properties of Ba(Hf_xTi_1 − x)O₃ (x = 0, 0.1, 0.2, 0.3, 0.4) (BHT) thin films deposited on platinized silicon and fused quartz substrates. Analyses of the X-ray diffraction patterns reveal that with the increase in Hf contents there is a systematic increase of the lattice constants of BHT films. Irrespective of the measurement frequencies the dielectric constants was found to be systematically decreased, whereas their frequency dispersion was found to be reduced with increasing Hf contents. The leakage current data measured using a metal-insulator–metal configuration reveal that the Schottky emission is the dominant leakage current mechanism in these films. BHT films, deposited on transparent fused quartz substrates, were also characterized in terms of their optical properties. For this purpose the transmittance of the undoped as well as Hf doped barium titanate thin films was measured as a function of wavelength in the range of 290 nm to 800 nm. The transmission spectra were analysed to estimate the wavelength dependence of the refractive indices/extinction coefficients as well as the variation of optical band gap of these films. With the increase of Hf contents, a systematic increase of the band gap [from 3.65 eV (undoped film) to 4.15 eV (40 at.% Hf doped barium titanate film)] was observed. The reduction of the leakage current with increasing hafnium substitution is discussed on the basis of an increasing Schottky barrier height and due to a simultaneous increase in the band gap of the material.     

Microstructural and optical properties of Ga-doped ZnO semiconductor thin films prepared by sol-gel process

Transparent thin films of Ga-doped ZnO (GZO), with Ga dopant levels that varied from 0 to 7 at.%, were deposited onto alkali-free glass substrates by a sol-gel process. Each spin-coated film was preheated at 300 °C for 10 min, and then annealed at 500 °C for 1 h under air ambiance. The effects of Ga dopant concentrations on crystallinity levels, microstructures, optical properties, and electrical resistivities of these ZnO thin films were systematically investigated. Photoluminescence spectra of GZO thin films were examined at room temperature. XRD results revealed that the undoped ZnO thin films exhibited a preferred orientation along the (002) plane and that the ZnO thin films doped with Ga showed degraded crystallinity. Experimental results also showed that Ga doping of ZnO thin films could markedly decrease surface roughness, improve transparency in the visible range, and produce finer microstructures than those of undoped ZnO thin films. The most promising films for transparent thin film transistor (TTFT) application produced in this study, were the 3 and 5 at.% Ga-doped ZnO thin films, both of which exhibited an average transmittance of 90.6% and an RMS roughness value of about 2.0 nm.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).     

Characterization on pulsed laser deposited nanocrystalline ZnO thin films

Nanocrystalline zinc oxide thin films were deposited on glass and silicon substrates by using pulsed laser deposition at different laser energy densities (1.5, 2, and 3 J/cm²). The film thickness, surface roughness, composition, optical and structural properties of the deposited films were studied using an α-step surface profilometer, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), optical transmittance, and X-ray diffraction (XRD), respectively. The film thickness was calculated as 244 nm. AFM analysis shows that the root-mean-square roughness increases with increasing laser energy density. XPS analysis shows that the interaction of zinc with oxygen atoms is greatly increased at high laser energy density. In the optical transmittance spectra, a shift of the absorption edge towards higher wavelength region confirms that the optical band gap increases with an increase in laser energy density. The particle size of the deposited films was measured by XRD, it is found to be in the range from 7.87 to 11.81 nm. It reveals that the particle size increases with an increase in laser energy density.     

Boron-doped transparent conducting nanodiamond films

Boron-doped nanodiamond (ND) films on silica substrates have been obtained by the method of microwave plasma-enhanced chemical vapor deposition (MWPECVD). Using special technological regimes ensuring the growth of boron-doped ND films after the deposition of an initial ND nucleation layer with small roughness (<15 nm) and a large number of diamond phase nucleation centers per unit surface area (>10¹⁰ cm⁻²), it is possible to obtain conducting ND films transparent in the UV spectral range. Dependence of the transparency and conductivity of the obtained films on the boron concentration and methane content in the working methane-hydrogen mixture has been studied.     

Effect of negatively charged species on the growth behavior of silicon films in hot wire chemical vapor deposition

The deposition behavior of silicon in hot wire chemical vapor deposition was investigated, focusing on the generation of negatively charged species in the gas phase using a gas mixture of 20% SiH₄ and 80% H₂ at a 450 °C substrate temperature under a working pressure of 66.7 Pa. A negative current of 6–21 µA/cm² was measured on the substrate at all processing conditions, and its absolute value increased with increasing wire temperature in the range of 1400 °C–1900 °C. The surface roughness of the films deposited on the silicon wafers increased with increasing wire temperature in the range of 1510 °C–1800 °C. The film growth rate on the positively biased substrates (+ 100 V, + 200 V) was higher than that on the neutral (0 V) and negatively biased substrates (− 100 V, − 200 V, − 300 V). These results indicate that the negatively charged species are generated in the gas phase and contribute to deposition. The surface roughness evolved during deposition was attributed to the electrostatic interaction between these negatively charged species and the negatively charged growing surface.     

Effects of Al content on the properties of ZnO:Al films prepared by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ZnO co-sputtering

Aluminum doped zinc oxide (AZO) films were deposited on quartz substrates by radio-frequency magnetron co-sputtering method with ZnO and Al₂O₃ ceramic targets. The structural, optical and electrical properties of these films as a function of the Al content were investigated. XRD results reveal that the AZO films are wurtzite structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in a wide wavelength range from 400 to 1,500 nm. The band gap energy, calculated from their optical absorption spectra, is in the range of 3.50–3.66 eV depending on the Al content. Doping of Al³⁺ in the ZnO makes the film surface roughness decrease. The dopant Al³⁺ acts as electron donor by which the electrical conductivity and carrier concentration of the films are obviously increased until the Al³⁺ reaches its saturation content of about 4.50 at.%.     

Pulsed laser deposition of conductive indium tin oxide thin films

Thin indium tin oxide (ITO) films have been grown on quartz glass substrates by pulsed laser deposition. The influence of ablation target composition and deposition conditions on the growth rate, optical transmission spectra, and carrier mobility and concentration of the films has been examined. The average surface roughness of the ITO films grown at substrate temperatures above 300°C is 2 nm. The films grown at an oxygen partial pressure of 5 mTorr using ablation targets with Sn/(In + Sn) = 5% possess high transmission (85-95%) in the visible range and low resistivity (1.8 × 10⁻⁴ Ω cm).     

Ammonia-free chemical bath deposition of nanocrystalline ZnS thin film buffer layer for solar cells

In this work, we prepared zinc sulfide thin films on glass substrates by ammonia-free chemical bath deposition method using thioacetamide as the sulfide source and Ethylene Diamine Tetra Acetic Acid disodium salt as the complexing agent in a solution of pH = 6.0. Thin films of ZnS with different thicknesses of 18–450 nm were prepared. The effect of film thickness and annealing temperature in atmospheric air, on optical properties, band gap energy and grain size of nanocrystals were studied. The X-ray diffraction analysis showed a cubic zinc blend structure and a diameter of about 2–5 nm for ZnS nanocrystals. The Fourier Transform Infrared spectrum of films revealed no peaks due to impurities. The as-deposited ZnS films had more than 70% transmittance in the visible region. The direct band gap of as-deposited films ranged from 3.68 to 3.78 eV and those of annealed films varied from 3.60 to 3.70 eV.     

Ultra-shallow junctions formed by quasi-epitaxial growth of boron and phosphorous-doped silicon films at 175 °C by rf-PECVD

In this paper, we use in-situ and ex-situ spectroscopic ellipsometry as an optical tool to optimize the process conditions that lead to epitaxial growth of undoped and doped silicon films in a standard radio-frequency Plasma Enhanced Chemical Vapor Deposition (rf-PECVD) reactor at temperatures below 200 °C. The influence of the plasma conditions (such as pressure, inter-electrode distance, hydrogen dilution and dopant precursor gas concentration) on the nature of the films is studied. This optimization allows us to achieve epitaxial growth of phosphorous-doped and boron-doped silicon films at temperatures as low as 175 °C and 140 °C, respectively. The epitaxial films possess thicknesses on the order of a few tens of nanometers, and sheet resistance values below 150 Ω/□. Annealing in air at 275 °C helps to further improve the conductivity of boron-doped layers. Four-point probe sheet resistance measurements and secondary ion mass spectrometry profiles are used to assess the dopant profile in the epitaxial layers. The junctions thus obtained are also characterized through their application in a solar cell, resulting in a fill factor over 76% and an efficiency exceeding 14%.     

脉冲激光沉积ZrW2O8薄膜的制备和性能

采用脉冲激光沉积法在石英基片上沉积制备了ZrW2O8薄膜.用X射线衍射仪(XRD)、原子力显微镜(AFM)研究了不同衬底温度对薄膜结构组分、表面粗糙度和形貌的影响,用台阶仪和分光光度计测量薄膜的厚度和不同衬底温度下制备薄膜的透射曲线,用变温XRD分析了ZrW2O8薄膜的负热膨胀特性.实验结果表明:在衬底温度为室温、550℃和650℃下脉冲激光沉积的ZrW2O8薄膜均为非晶态,非晶膜在1200℃保温3min后淬火得到立方相ZrW2O8薄膜;随着衬底温度的升高,ZrW2O8薄膜的表面粗糙度明显降低;透光率均约为80%,在20～600℃温度区间内,脉冲激光沉积制备的ZrW2O8薄膜的负热膨胀系数为-11.378×10-6 K-1.     

Optical properties of SnO2:F films deposited by atmospheric pressure CVD

Atmospheric pressure chemical vapor deposition (APCVD) system, designed for the deposition of F-doped SnO₂ thin films, is compatible with industrial requirements such as high process speed, scaling to wide substrate widths and low costs. Precise method for measuring the optical absorptance in the spectral range 300–1700 nm combines transmittance, reflectance and photothermal deflection (PDS) spectra measured on the same spot of the sample immersed in the transparent liquid with a relatively high index of refraction. The effects of the film thickness, doping gas addition and the susceptor temperature on the optical absorptance and electrical resistivity of the TCO films are assessed. We show that the doping gas concentration and the susceptor temperature influence both the incorporation ratio of dopants into SnO₂ film as well as the defect concentration. The SnO₂ films growth at optimum APCVD conditions have thickness 0.7 µm, average surface roughness about 40 nm, sheet electrical resistance 10 Ω/sq and the optical absorption 1% at 500 nm and about 5% at 1000 nm.     

Polycrystalline AlN films with preferential orientation by plasma enhanced chemical vapor deposition

AlN thin films for acoustic wave devices were prepared by Microwave Plasma Enhanced Chemical Vapor Deposition under different process conditions, employing Si (100) and Pt (111)/SiO₂/Si (100) substrates. The films were characterized by X-ray diffraction, Fourier transform infrared transmission spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The values of the distance between the plasma and the tri-methyl-aluminum precursor injector, the radiofrequency bias potential, and the substrate temperature were central in the development of polycrystalline films. The choice of the chamber total pressure during deposition allowed for the development of two different crystallographic orientations, i.e., <0001> or <1010>. The film microstructures exhibited in general a column-like growth with rounded tops, an average grain size of about 40 nm, and a surface roughness lower than 20 nm under the best conditions.     

偏压对ITO薄膜生长模式和光电性能的影响

为明确溅射偏压对ITO薄膜性质的影响,用射频磁控溅射法于室温在玻璃衬底制备出ITO透明导电薄膜,研究了不同偏压下ITO薄膜的生长模式、光学和电学性能.结果表明:随着偏压的增加,薄膜沉积模式经历了沉积、沉积和扩散、表面脱附3种方式;AFM和SEM显示,偏压为100 V时,膜层表面光洁、均匀,粗糙度最小,均方根粗糙度为1.61 nm;XRD分析表明偏压会影响与薄膜的择优取向,偏压为100 V时,薄膜晶粒取向为(222)面;薄膜偏压为120 V时,薄膜的光电性能最佳,电阻率最低为2.59×10-4Ω.cm,可见光区的平均透过率在85%以上;偏压的大小使薄膜的吸收边发生了"蓝移"或"红移".     

Growth properties of AlN films on sapphire substrates by reactive sputtering

Aluminum nitride (AlN) films were grown on sapphire substrates by radio frequency (RF) magnetron sputtering in plasma containing a mixture of argon and nitrogen, using a pure aluminum target. The effect of RF power was investigated with respect to growth rate, surface roughness, and transmittance of AlN films. As the RF power increases, the growth rate increases and the root mean square of surface roughness decreases while the absorption edge shifts to longer wavelength. This shift is believed to be due to the defects induced by ion bombardment.     

F-doped SnO2 thin films grown on flexible substrates at low temperatures by pulsed laser deposition

Fluorine-doped tin oxide (SnO₂:F) films were deposited on polyethersulfone plastic substrates by pulsed laser deposition. The electrical and optical properties of the SnO₂:F films were investigated as a function of deposition conditions such as substrate temperature and oxygen partial pressure during deposition. High quality SnO₂:F films were achieved under an optimum oxygen pressure range (7.4-8 Pa) at relatively low growth temperatures (25-150 °C). As-deposited films exhibited low electrical resistivities of 1-7 mΩ-cm, high optical transmittance of 80-90% in the visible range, and optical band-gap energies of 3.87-3.96 eV. Atomic force microscopy measurements revealed a reduced root mean square surface roughness of the SnO₂:F films compared to that of the bare substrates indicating planarization of the underlying substrate.     

Europium incorporated barium titanate thin films for optical applications

BaTiO₃:Eu (BT:Eu) thin films were deposited onto quartz substrates by RF magnetron sputtering. The effect on structural, morphological, optical and photoluminescence (PL) properties in the films with different Eu concentrations (0–5 wt%) were investigated. The X-ray diffraction (XRD) pattern of the undoped BT thin film revealed a tetragonal (T) phase with orientations along (101) plane. From XRD pattern, the crystallinity of the films increased with increase in Eu concentration. The SEM images revealed that the films exhibited tetragonal shape, crack free and good adherence to the substrate. Atomic force microscopy studies showed an increase of grain growth with doping concentration. The rms roughness value increased with increase in Eu concentration and the film surface revealed positive skewness and high value of kurtosis which make them suitable for tribological applications. X-ray photoelectron spectroscopy revealed the presence of barium, titanium, europium and oxygen in BT:Eu film. An average transmittance of >80 % (in visible region) was observed for all the films. Optical band gap of Eu doped BT films decreased from 3.86 to 3.53 eV. Such films with optical properties such as high transparency, decrease in band gap and high refractive index are suitable for optoelectronic applications. PL properties showed a sharp line at 625 nm and a broad line at 552 nm due to europium (Eu³⁺) transitions. PL phenomena were observed, owing to the electronic structure of Eu³⁺ ions as well as BT nanocrystallites in the films. The sharp and intense red luminescence is useful for photoelectric devices and optical communications.     

Optical properties of porous anodic aluminum oxide thin films on quartz substrates

Porous anodic aluminum oxide (AAO) thin films on quartz substrates were fabricated via evaporation of a 100-nm thick Al, followed by anodization with different durations and pore widening and Al removal by chemical etching. The transmittance and reflectance of AAO films on quartz substrates were measured by optical spectrophotometry. The microstructure and morphology were examined by scanning electron microscopy. The pore diameter of AAO films after pore widening and Al removal is 60 ± 4 nm and the interpore distance is 88 ± 5 nm. It is found that the reflectance decreases and the transmittance increases with the increase of the anodization time and pore widening. Compared to a bare substrate, the transmittance of AAO films after pore widening and Al removal is about 3.0% higher, while the reflectance is about 3.0% lower over a wide wavelength range. Additionally, after pore widening and Al removal, when AAO films are prepared on both sides of the quartz substrate, the highest transmittance is about 99.0% in the wavelength range 570-680 nm. The optical constants and thickness of AAO films after pore widening and Al removal were retrieved from normal incidence transmittance data. Results show that the refractive index is lower than 1.25 in the visible optical region and that the porosity is about 0.70.     

Enhanced deposition of cubic boron nitride films on roughened silicon and tungsten carbide-cobalt surfaces

We report the influence of substrate surface roughness on cubic boron nitride (cBN) film deposition under low-energy ion bombardment in an inductively coupled plasma. Silicon and cemented tungsten carbide-cobalt (WC-Co) surfaces are roughened by low-energy ion-assisted etching in a hydrogen plasma, followed by deposition in a fluorine-containing plasma. Infrared absorption coefficients are measured to be 22,000 cm⁻¹ and 17,000 cm⁻¹ for sp²-bonded BN and cBN phases, respectively, for our films. For the silicon substrates, the film growth rate and the cBN content in the film increase with increasing the surface roughness, while the amount of sp²BN phase in the film shows only a small increase. A larger surface roughness of the substrate results in a smaller contact angle of water, indicating that a higher surface free energy of the substrate contributes to enhancing growth of the cBN film. For the WC-Co substrates, the film growth rate and the cBN content in the film increase similarly by roughening the surface.     

由红外透过谱确定金刚石膜的光学常数及相关因素

结合金刚石膜的具体情况,考虑到色散效应、膜的微结构、表面粗糙度及样品中自由载流子和C-H的吸收等多种因素对红外透过谱的影响,在无吸收单层膜透过率模型的基础上进行了修正,给出了自支撑金刚石薄膜透过率的数学模型.并对不同制备方法和工艺参数下沉积的金刚石膜的红外透过谱用Levenberg-Mar-quardt算法进行非线性最小二乘拟合,从而确定出样品的红外光学常数和其它影响透过率的因素.这些结果对正确分析金刚石薄膜的红外光学性质是很重要的.