Optimum packing density and crystal structure of tin-doped indium oxide thin films for high-temperature annealing processes

The influence of high-temperature annealing on the electrical properties and microstructure of tin-doped indium oxide (ITO) thin films was investigated as a function of oxygen gas flow ratio to argon gas during the sputtering deposition. The ITO thin films were annealed at 500 °C in air after the deposition. It was found that the ITO thin films, which were deposited in relatively low oxygen gas flow ratio, exhibited high Hall mobility and low-resistivity after the annealing. Furthermore, the X-ray reflectivity and diffraction measurement revealed that the ITO thin film with low-resistivity after annealing exhibited high packing density, smooth surface and low crystallization degree. It can be considered that the carrier electron scattering was suppressed with increasing in the packing density of the ITO thin film; as a result, the Hall mobility and resistivity were improved.     

Structural and optical properties of pulsed laser deposited SrBi2Nb2O9 thin films

SrBi₂Nb₂O₉ (SBN) thin films were prepared on fused quartz substrates at room temperature by pulsed laser deposition. The influence of deposition parameters such as target-to-substrate distance, oxygen pressure and annealing temperature on film crystallization behavior was investigated by X-ray diffraction. Results indicated that the films grown at the optimum processing conditions have polycrystalline structure with a single layered perovskite phase. The optical transmittance of the films prepared at various oxygen pressures was measured in the wavelength range 200–900 nm using UV–vis spectrophotometer. The results showed that there is a red shift in the optical absorption edge with a rise in the oxygen pressure. Refractive index as a function of wavelength and optical band gap of the films were determined from the optical transmittance spectra. The results indicated that the refractive index increases with increasing oxygen pressure at the same incident light wavelength, while the band gap reduces from 4.13 to 3.88 eV. It may be attributed to an increase in packing density and grain size, and decrease in oxygen defects.     

Surface and interface characteristics of TiO2–muscovite nanocomposites

The morphology and chemical characteristics of the surface and the interface of TiO₂–muscovite nanocomposites were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Our results clearly showed that TiO₂ grains formed on the TiO₂ thin film surface, whereas the presence of TiO₂ grains on the interface between TiO₂ thin films and the muscovite substrates was not obvious. While euhedral rutile grains were found in samples doped with Zn ions, none were found in samples doped with Sn ions. The XPS results showed that cations present in the muscovite substrates diffused into the TiO₂ thin films. Etching measurements revealed that diffusion abilities of cation impurities varied: Si and Al diffused more easily than K. The observed differences in chemical composition and oxidation of the elements, especially on the surface and the subsurface, may influence the different crystallization behaviors of elements in TiO₂ thin films and the different active degree of elements diffusing from muscovite substrates.     

Effect of annealing temperature on microstructure of chemically deposited calcium modified lead titanate thin films

Thin ferroelectric films of calcium modified lead titanate Pb_1−xCa_xTiO₃(PCT) have been prepared by chemical deposition process. The as deposited amorphous films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various amounts of calcium (Ca)-doping (0.20, 0.24, and 0.28) on indium tin oxide (ITO) coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out at various annealing temperatures (450, 550, and 650 °C). Characterization of these films by XRD shows that the films exhibit tetragonal phase with perovskite structure. Atomic force microscope images (AFM) are characterized by slight surface roughness with a uniform crack-free, densely-packed structure. Also, Fourier transform infrared spectra (FT-IR) of the as deposited film and annealed thin films (x=0.24) at 650 °C on silicon (Si) substrates were taken to get more information about the film formation. Dielectric studies of the films were carried out and reported.     

Cuprite, paramelaconite and tenorite films deposited by reactive magnetron sputtering

Copper oxides films (Cu₂O, Cu₄O₃ and CuO) have been deposited by magnetron sputtering of a copper target in various Ar–O₂ reactive mixtures. The films are characterized by X-ray diffraction, scanning electron microscopy, four-point probe method and UV-Vis spectrometry. The three defined compounds in the Cu---O binary system can be deposited by varying the oxygen flow rate introduced into the reactor. All the films are crystallized with a mean crystal size ranging from 10 to about 35 nm. They are highly resistive and present a direct optical band gap higher than 2 eV. The application of a bias voltage during the deposition phase modifies the texture of the Cu₂O films and also induces a preferential resputtering of oxygen from the Cu₄O₃ ones. This resputtering phenomenon leads firstly to the occurrence of the cuprite phase mixed with the paramelaconite one and secondly to the amorphisation of the films. Finally, the thermal stability in air of cuprite, paramelaconite and tenorite films has been investigated. The results show that the stability of Cu₂O and Cu₄O₃ films in air is influenced by the thickness and/or the texture of the films. Tenorite films with a low optical band gap (1.71 eV) can be formed after air annealing at 350 °C of an unbiased cuprite film.     

Transparent conductive oxide thin films of CdTe-doped indium oxide prepared by pulsed-laser deposition

Transparent conducting oxide thin film CdTe-doped indium oxide (In₂O₃) has been grown by pulsed-laser deposition from a target of CdTe powder embedded in metallic indium. The electro-optical and structural properties were investigated as a function of oxygen partial pressure (PO₂) and substrate temperature (T_s). A film deposited at T_s=420 °C and PO₂=4 Pa shows the minimum resistivity 7.5×10⁻⁴ Ω cm, its optical transmission is 83% and the carrier concentration was 8.9×10²⁰ cm³. The optical band gap and the average roughness of that sample were 3.6 eV and 6.45 Å, respectively. X-ray diffraction studies indicated that the films were polycrystalline. This material is a good candidate for being used as transparent conductor in the CdTe–CdS solar cell.     

Ellipsometry investigation of the effects of annealing temperature on the optical properties of indium tin oxide thin films studied by Drude-Lorentz model

Float glass substrates covered by high quality ITO thin films (Balzers) were subjected for an hour to single thermal treatments at different temperature between 100 °C and 600 °C. In order to study the electric and optical properties of both annealed and not annealed ITO-covered float glasses, ellipsometry, spectrophotometry, impedance analysis, and X-ray measurements were performed. Moreover, variable angle spectroscopic ellipsometry provides relevant information on the electronic and optical properties of the samples. ITO film is modeled as a dense lower layer and a surface roughness layer. The estimated optical density for ITO and the optical density of the surface roughness ITO layer increases with the annealing temperature. In the near-IR range, the extinction coefficient decreases while the maximum of the absorption in the near UV range shift towards low photon energy as the annealing temperature increases. Spectrophotometry was used to estimate the optical band-gap energy of the samples. The thermal annealing changes strongly the structural and optical properties of ITO thin films, because during the thermal processes, the ITO thin film absorbs oxygen from air. This oxygen absorption decreases the oxygen vacancies therefore the defect densities in the crystalline structure of the ITO thin films also decrease, as confirmed both by ellipsometry and X-ray measurements.     

脉冲偏压电弧离子镀Cr-O薄膜结构及光学性能研究

采用脉冲偏压电弧离子镀技术在单晶硅基片及石英玻璃上制备了一系列均匀透明的Cr-O薄膜. 用场发射扫描电子显微镜、X射线衍射仪、X射线光电子谱、纳米压痕仪、紫外可见光分光光度计等方法对薄膜的表面形貌、膜厚、相结构、成分、元素的化学价态、硬度和光学性能等进行表征, 主要研究了偏压幅值对薄膜结构和性能的影响. 结果表明, 施加偏压可使薄膜的沉积质量明显提高, 其相结构由非晶态转变为晶体态, 并随着偏压幅值的增加, 由Cr₂O₃相向CrO相转变; 薄膜的硬度先增大后减小, 当偏压为-300 V时, 硬度达到最大值24.4 GPa; 薄膜具有良好的透光率, 最高可达72%; 当偏压为-200 V时, 薄膜的最大光学帯隙为1.88 eV.     

Growth and characterization of MOMBE grown HfO2

HfO₂ dielectric layers were grown directly on the p-type Si (1 0 0) by metalorganic molecular beam epitaxy (MOMBE). Hafnium tetra-butoxide was used as a Hf precursor and pure oxygen was introduced to form an oxide layer. The properties of the layers with different thicknesses were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and capacitance–voltage (C–V) and current–voltage (I–V) analyses. XRD and HRTEM results showed that the HfO₂ films thinner than 12 nm were amorphous while the films thicker than 12 nm began to crystallize in the tetragonal and the monoclinic phases. The XPS spectra of O 1s show that the O---Si binding energies shifted to the lower binding energy with increasing the HfO₂ layer thickness. Moreover, the snap back phenomenon is observed in accumulation capacitance. These changes are believed to be linked with the decomposition of SiO and the crystallization of HfO₂ layer during the film growth.     

Work function changes and surface chemistry of oxygen, hydrogen, and carbon on indium tin oxide

The surface chemistry of indium tin oxide (ITO) has been investigated with Auger electron spectroscopy (AES) and high resolution electron energy loss spectroscopy (HREELS). A vibrating Kelvin probe (KP) with a graphite reference was used to monitor the absolute work function (Φ) of ITO as a function of chemical modification. The ITO was exposed in situ to molecular hydrogen (H₂), hot-filament-activated oxygen (O₂^*), and hot-filament-activated deuterium (D₂^*). The initial Φ of ITO was determined to be 5.2 eV, and surface chemical changes had strong effects on this value, as seen by KP. Exposure of clean ITO to O₂^* increased Φ to 5.6 eV, but the increase was short-lived. The changes in Φ over time were correlated with the uptake of carbon impurities in ultra high vacuum (UHV), as monitored by AES.

The HREELS of ITO revealed significant hydrocarbon impurities. Chemical reduction of ITO produced a metallic surface and dehydrogenated the adsorbed hydrocarbons. Both re-oxidation of metallic ITO and oxidation of clean ITO temporarily removed adventitious carbon from the surface, but oxidized ITO adsorbed an even larger quantity of carbon over time.     

Chemical and structural analysis of low-temperature excimer-laser annealing in indium-tin oxide sol-gel films

We investigated the influence of excimer-laser annealing (ELA) on the electrical, chemical, and structural properties of indium–tin oxide (ITO) films prepared by a solution process. The ITO film was prepared by the sol-gel method and annealed by excimer-laser pulses with an energy density up to 240?mJ/cm². Hall measurements showed that the ELA substantially enhanced the electrical properties of the ITO films, including their resistivity, carrier density, and mobility, as increasing the laser energy density. In-depth x-ray photoelectron spectroscopy analysis of the chemical states in the film surface showed that the ELA reduced carbon species and promoted both an oxidation and crystallization. These changes were consistent with results of x-ray diffraction and transmission electron microscopy measurements, where expansions in the microcrystal growth were observed for higher laser energy density. We comprehensively understand that the chemical rearrangement and concomitant crystallization are the main factors for achieving the electrical properties during the ELA. These results suggest the potential of the ELA-treated sol-gel films for providing high-quality ITO films at low temperatures toward the flexible device applications.     

Strain effects in epitaxially grown La0.7Sr0.3MnO3 thin films

We report here on an X-ray absorption study of La_0.7Sr_0.3MnO₃ films epitaxially grown on SrTiO₃ substrate. The local organization around Mn in oriented films with 600 Å in thickness was investigated by polarized Extended X-ray Absorption Fine Structure. The angle between electric field vector and film surface was set equal to 5° and 70° to investigate almost independently the contribution of the manganese neighbors situated in and out of the film plane. The first neighboring shell oxygen is found to be the same in both geometries, but small changes in the next neighboring contribution are observed. These changes are associated with variation in the Mn–Mn bond length. A small in-plane elongation (3%) is observed in the constrained films with respect to the unconstrained case.     

Co/Co3O4/PZT多铁复合薄膜的交换偏置效应及其磁电耦合特性

本文采用溶胶-凝胶工艺并结合脉冲激光沉积技术, 在Pt/Ti/SiO₂/Si衬底上制备了Co/Co₃O₄/PZT多铁复合薄膜. 对复合薄膜的微结构和组分进行了表征, 并系统研究了复合薄膜中的交换偏置效应及其对磁电耦合作用的影响. 研究结果表明, 复合薄膜在77 K具有明显的交换偏置效应, 交换偏置场达到80 Oe, 且交换偏置场及矫顽场均随温度降低而增大. 当温度降低到10 K时, 交换偏置场增至160 Oe. X射线光电子能谱(XPS)测试结果证实在Co和Co₃O₄界面处存在约5 nm厚的CoO层, 表明77 K下的交换偏置效应源自反铁磁的CoO层对Co的钉扎作用. 观察到复合薄膜的电容-温度曲线随着外加磁场大小和方向的改变而呈现出规律性的变化, 表明复合薄膜存在磁电耦合效应. 进一步研究发现, 在低温下复合薄膜呈现出各向异性的磁电容效应, 与磁场大小和方向密切相关. 复合薄膜的这种磁电耦合特性主要与复合体系的交换偏置效应及基于界面应力传递的磁电耦合作用有关, 本文对其中的物理机理进行了详细讨论与分析.     

In_2O_3:Sn中间层改善B掺杂ZnO薄膜的性能及其应用研究

金属有机化学气相沉积(MOCVD)法生长的掺硼氧化锌(BZO)薄膜,具有天然的"类金字塔"绒面结构,作为硅基薄膜太阳电池的前电极具有良好的陷光效果.但直接获得的BZO薄膜表面形貌过于尖锐,影响后续硅基薄膜材料生长质量及太阳电池的光电转换效率.本文设计了以一层超薄In2O3:Sn(ITO)薄膜(～4 nm厚度)作为中间层的多层膜,并通过对顶层BZO薄膜的厚度调制,改善BZO薄膜的表面特性,薄膜结构为:glass/底层BZO/ITO/顶层BZO.合适厚度的顶层BZO薄膜有助于获得类似"菜花状"形貌特征,尖锐的表面趋于"柔和",而较厚的顶层BZO薄膜仍然保持"类金字塔状"结构."柔和"的BZO薄膜表面结构有助于提高后续生长薄膜电池的结晶质量.将获得的新型"三明治"结构多层膜应用于p-i-n型氢化微晶硅(μc-Si:H)薄膜太阳电池,相比传统的BZO薄膜,电池的量子效率QE在500—800 nm波长范围提高了～10%,并且电池的Jsc和Voc均有所提高.     

Effects of substitution of Ti for Fe in BiFeO3 films prepared by sol–gel process

Ti substituted BiFe_1−xTi_xO_3+δ films have been prepared on indium–tin oxide (ITO)/glass substrates by the sol–gel process. The films with x=0.00–0.20 were prepared at an annealing temperature of 600 °C. X-ray diffraction patterns indicate that all films adopt R3m structure and the films with x=0 and 0.10 show pure perovskite phase. Cross-section scanning shows the thickness of the films is about 300 nm. Through 0.05 Ti substitution, the 2P_r increases to 8.30 μC/cm² from 2.12 μC/cm² of the un-substituted BiFeO₃ film and show enhanced ferroelectricity at room temperature. The 2P_r values are 2.63 and 0.44 μC/cm² for the films with x=0.01 and 0.2, respectively. Moreover, the films with x=0.05 and 0.10 show enhanced dielectric property since the permittivity increases near 150 at the same measuring frequency. Through the substitution of Ti, the leakage conduction is reduced for the films with x=0.05–0.20.     

Oxidation and thermal annealing effects on native and ion-irradiated PbTe films grown by molecular beam deposition

Investigations are reported into the effect of low-pressure oxygen exposure and thermal annealing on the carrier transport properties of native and 350 eV Ar⁺ bombarded PbTe films. The electrical measurements were madein situ on MBD-grown PbTe films without breaking vacuum. On native surfaces, oxidation was initially sustained by diffusion of a donor species from the film bulk to the surface, where reaction with oxygen occured. This diffusion process was apparently inhibited on ion irradiated films and direct doping of the film surface effected a gradual reduction in the ion-induced electron accumulation resident at the film surface. The native properties and behavioural characteristics of the films could be recovered by thermal annealing of the ion-irradiated and/or oxidized films at 300–350 °C.     

Argon ion stimulated conversion between CFx (x = 0–3) chemical states and fluorine depletion in fluorocarbon films studied by X-ray photoelectron spectroscopy

Surface chemical composition of fluorocarbon films deposited onto indium-tin-oxide (ITO) substrates was modified by 2.0 keV Ar⁺ irradiation with doses of up to 2.6×10¹³ ions/cm². The effect of ion irradiation on the chemical composition and bonding configuration of the upper-surface and sub-surface regions were monitored by high-resolution angle-resolved X-ray photoelectron spectroscopy (AR-XPS). It was found that the as-deposited films compose of a distribution of CF, CF₂, CF₃ and C–C chemical states. C 1s line-shape analysis of XPS spectra measured at grazing and normal emission angles shows that as a result of the irradiation, the population of the CF₃ and CF₂ chemical states were preferentially depleted from the film’s surface resulting in an increased population of the CF and C–C chemical states in the upper-surface region of the film. It is suggested that low energy ion irradiation can be used to chemically modify the surface of fluorocarbon films.     

HF sputtered indium oxide films doped with tin

Indium-tin-oxide films (ITO films) sputtered in Ar-atmosphere with and without addition of oxygen reveal an irreversible increase in conductivity during annealing in vacuum. This annealing process increases drastically the density of free electrons, while the Hall mobility changes only slightly. Below the annealing temperature the temperature dependence of the conductivity is reversible. In films with low density of free electrons, which behave like non-degenerated semiconductors, two activation energies for the mobility could be found. The irreversible changes, observed during annealing in the vacuum, are explained by diffusion of oxygen from the interior of the film to the surface, followed by desorption of the oxygen from the surface into the vacuum. The excess oxygen in the non-stoichiometric films plays the role of electron traps. The irreversible effects during annealing in the vacuum are partly reversible in the long run. If the annealed films are exposed to oxygen or air their conductivity decreases because of diffusion of oxygen from the surface into the film.     

Conducting properties of In2O3:Sn thin films at low temperatures

Electrical conductivity, Hall effect and magnetoresistance of In₂O₃:Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, have been investigated in the temperature range 4.2–300 K. The observed temperature dependences of resistivity for films deposited at 230 °C as well as at nominally room temperatures were typical for metallic transport of electrons except temperature dependence of resistivity of the In₂O₃:Sn film deposited in the oxygen deficient atmosphere. The electrical measurements were accompanied by AFM and SEM studies of structural properties, as well as by XPS analysis. It is established that changes of morphology and crystallinity of ITO films modify the low-temperature behavior of resistivity, which still remains typical for metallic transport. This is not the case for the oxygen deficient ITO layer. XPS analysis shows that grown in situ oxygen deficient ITO films have enhanced DOS between the Fermi level and the valence band edge. The extra localized states behave as acceptors leading to a compensation of n-type ITO. That can explain lower n-type conductivity in this material crossing over to a Mott-type hopping at low temperatures. Results for the low temperature measurements of stoichiometric ITO layers indicate that they do not show any trace of metal-to-insulator transition even at 4.2 K. We conclude that, although ITO is considered as a highly doped wide-band gap semiconductor, its low-temperature properties are very different from those of conventional highly doped semiconductors.     

Oxygen diffusion through thin Pt films on Si(100)

We have investigated the diffusion of oxygen through evaporated platinum films on Si(100) upon exposure to air using substrates covered with Pt films of spatially and continuously varying thickness (0–500 Å). Film compositions and morphologies before and after silicidation were characterized by modified crater edge profiling using scanning Auger microscopy, energy-dispersive X-ray microanalysis, scanning tunneling microscopy, and transmission electron microscopy. We find that oxygen diffuses through a Pt layer of up to 170 Å forming an oxide at the interface. In this thickness range, silicide formation during annealing is inhibited and is eventually stopped by the development of a continuous oxide layer. Since the platinum film consists of a continuous layer of nanometer-size crystallites, grain boundary diffusion of oxygen is the most probable way for oxygen incorporation. The diffusion constant is of the order of 10^–19 cm²/s with the precise value depending on the film morphology.