Conductivity and current-voltage characteristics of PZT thin-film heterostructures

The conductivity of thin-film Pt/PZT/Pt structures has been studied using the method of current-voltage characteristics. The asymmetry of current-voltage characteristics has been revealed, which indicates that the potential barriers at the interfaces between the studied structures are different, and this asymmetry changes depending on the conditions of synthesis. It has been found that the current-voltage curve on semilogarithmic scales has several linear regions, which gives evidence that several mechanisms determine the conductivity of this structure. Two main conductivity mechanisms have been determined: ohmic mechanism and Frenkel-Poole emission. The conductivity of these structures increases with an increase in temperature, but the shape of the current-voltage characteristics remains unchanged.     

Structure of interfaces in thin-film metallic multilayer heterostructures

It is demonstrated that the structure of interfaces in thin-film metallic multilayers can be predicted from the phase diagrams of binary alloys of metals constituting the multilayers. Experimental data on the small-angle X-ray reflectivity and magnetization of the samples are used for characterizing the structure of the interfaces.     

Investigation of the electrical properties and stability of HfInZnO thin-film transistors

In this study, amorphous HfInZnO (a-HIZO) thin films and related thin-film transistors (TFTs) were fabricated using the RF-sputtering method. The effects of the sputtering power (50–200 W) on the structural, surface, electrical, and optical properties of the a-HIZO films and the performance and NBIS stability of the a-HIZO TFTs were investigated. The films’ N_e increased and resistivity decreased as the sputtering power increased. The 100 W deposited a-HIZO film exhibited good optical and electrical properties compared with other sputtering powers. Optimization of the 100 W deposited a-HIZO TFT demonstrated good device performance, including a desirable μ_FE of 19.5 cm²/Vs, low SS of 0.32 V/decade, low V_th of 0.8 V, and high I_on/I_off of 10⁷, respectively. The 100 W deposited a-HIZO TFT with Al₂O₃ PVL also exhibited the best stability, with small V_th shifts of -2.2 V during NBIS testing. These high-performance a-HIZO thin films and TFTs with Al₂O₃ PVL have practical applications in thin-film electronics.     

A novel hydrate-based thin-film phosphor: low-temperature growth process and properties

Thin films of barium chloride hydrate doped with cerium were deposited by spray pyrolysis of aqueous solutions. The cathodoluminescence (CL) spectrum consists of two peaks at 443 and 485 nm due to 4f–5d transitions of the cerium ion in thin films without post-heat treatment. The CL depended dramatically on deposition temperature between 250 °C and 500 °C. The phenomenon is directly related to the change of crystallinity and Cl concentration of the thin films. The CL spectra of thin films of BaCl₂·2H₂O:Ce were compared on various substrates. The relaxation behavior of CL was also observed in thin-film phosphor. Our results indicate that the material studied as thin-film phosphor is unique since it contains water. It seems that the 4f–5d transition in Ce is so energetic that the O–H phonons cannot disturb it, indicating that barium chloride hydrate is a novel host in which Ce has a higher efficiency. PACS 78.20.-e; 78.60.Hk; 85.60.JbThis revised version was published online in January 2005 with the addition of a second address and acknowledgements.     

Generation and evolution of partial misfit dislocations and stacking faults in thin-film heterostructures

An analysis is made of the specific features in the generation and evolution of partial misfit dislocations at the vertices of V-shaped configurations of stacking fault bands, which terminate in the bulk of the growing film at 90° partial Shockley dislocations. The critical thicknesses h _c of an epitaxial film, at which generation of such defect configurations becomes energetically favorable, are calculated. It is shown that at small misfits, the first to be generated are perfect misfit dislocations and at large misfits, partial ones, which are located at the vertices of V-shaped stacking-fault band configurations emerging onto the film surface. Possible further evolution of stacking-fault band configurations with increasing film thickness are studied.     

Investigation of structural and optical properties of ZnO films co-doped with fluorine and indium

Undoped ZnO film and ZnO films, which are co-doped with F and In (FIZO) at different concentrations, were synthesized by sol–gel technique and the effects of co-doping of F and In on structural and optical properties of ZnO thin films were investigated. The concentration ratio of [F]/[Zn] was altered from 0.25 to 1.75 with 0.50 step at.% mole and [In]/[Zn] was altered from 0.25 to 1.00 with 0.25 step at.% mole. X-ray diffraction analysis indicates that the films have polycrystalline nature and the (0 0 2) preferred orientation is the stronger peak. No extra phases involving zinc, fluorine and indium compounds were observed even at high F and In content. The grain size of undoped ZnO and FIZO thin films varied between 15 and 20 nm with a small fluctuation. From the SEM images, although the undoped ZnO had a smooth and particle-shaped surface, FIZO films had nanofiber-networks shapes over the surface with average size of 500 nm. The surface morphologies and crystallite sizes for the F and In doped films were slightly different from than those of undoped film. From the optical study, a slight shrinkage of band gap was backwardly observed from 3.36 to 3.25 eV with the increasing of F and In content.     

Simulation of the indium profile in InGaAs/GaAs quantum-size heterostructures

A new approach to describe phenomena attendant on the growth of thin InGaAs epitaxial layers by hydride MOCVD in terms of which the boundary gas layer is considered as quasi-liquid is suggested. A numerical model for simulating the concentration profiles of the components in quantum-well heterostructures is developed. It is based on the assumption that a state close to thermodynamic equilibrium exists near the interface. The concentration profiles are simulated by jointly solving equations that describe heterogeneous equilibria and material balance at the interface. The indium profiles in InGaAs/GaAs quantum-size heterostructures are simulated at various parameters of the epitaxy process, such as temperature, initial component ratio in the gas phase, and boundary layer thickness. The results obtained agree well with the available experimental data.     

Resonant tunneling properties of heterostructures

A general theory of resonance tunneling in planar structures, independent of the detailed form of the “well”, is developed. The transmission probability versus energy is Lorentzian, near each quasi-local level, with a width that is simply related to the lifetime for escape from the local state, the wave-packet transit time, and the dynamical response time. The charge-accumulation effect is estimated.     

Water-based processed and alkoxide-based processed indium oxide thin-film transistors at different annealing temperatures

In this study,indium oxide(In_2O_3) thin-film transistors(TFTs) are fabricated by two kinds of low temperature solution-processed technologies(Ta ≤ 300?C),i.e.,water-based(DIW-based) process and alkoxide-based(2-ME-based)process.The thickness values,crystallization properties,chemical structures,surface roughness values,and optical properties of In_2O_3 thin-films and the electrical characteristics of In_2O_3 TFTs are studied at different annealing temperatures.Thermal annealing at higher temperature leads to an increase in the saturation mobility(μsat) and a negative shift in the threshold voltage(VTH).The DIW-based processed In_2O_3-TFT annealed at 300?C exhibits excellent device performance,and one annealed at 200?C exhibits an acceptable μsat of 0.86 cm~2/V·s comparable to that of a-Si:H TFTs,whereas the 2-ME-based TFT annealed at 300?C exhibits an abundant μsat of 1.65 cm~2/Vs and one annealed at 200?C is inactive.The results are attributed to the fact that the DIW-based process induces a higher degree of oxidation and less defect states than the 2-ME-based process at the same temperature.The DIW-based process for fabricating the In_2O_3 TFT opens the way for the development of nontoxic,low-cost,and low-temperature oxide electronics.     

Conductivity and barrier effects in thin-film PZT-based heterostructures, depending on the conditions of synthesis

Electrical conductivity and dielectric characteristics in Pt/Pb(Zr_0.54,Ti_0.46)O₃/Pt film structures synthesized at different temperatures are studied. Volt-ampere (I–V) and volt-farad (C–V) characteristics are obtained. Asymmetry of the I–V characteristics is revealed, indicating a difference in the potential barriers at the interfaces of the analyzed structures that varies depending on the synthesis conditions. The values of the potential barriers at the Pt/PZT interfaces were calculated from the C–V characteristics. Two key conductivity mechanisms, Ohmic and Poole-Frenkel emission, were noted.     

Magnetic properties of epitaxial oxide heterostructures

Diluted Magnetic Semiconductors (DMS) are of great interest as injection sources for spin-polarized currents into semiconductors. Epitaxial devices have been synthesized with an intermediate spacer layer of the same semiconductor (zinc oxide, ZnO) used to produce the DMS material (ZnCoO) ensuring a homoepitaxial junction to help reduce the interface states and conduction mismatch. We observe a large magnetoresistance of about 32% in the devices at low temperatures. The present work suggests that spin polarized transport could be achieved with DMS materials acting as the source of injected spins into a non-magnetic host.     

Optical properties of alumina membranes prepared by anodic oxidation process

The luminescence property of anodic alumina membranes (AAMs) with ordered nanopore arrays prepared by electrochemically anodizing aluminum in oxalic acid solutions have been investigated. Photoluminescence emission (PL) measurement shows that a blue PL band occurs in the wavelength ranges of 300-600 nm. The PL intensity and peak position of AAMs depend markedly on the excitation wavelength. A new peak located at 518 nm can be observed under a monitoring wavelength at 429 nm in the photoluminescence excitation (PLE) spectra. Convincing evidences have been presented that the PLE would be associated with the residual aluminum ions in the membrane. The PLE and PL of AAMs, as a function of anodizing times, have been discussed. It is found that the oxalic impurities incorporated in the AAMs would have important influences on the optical properties of AAMs in the initial stage of anodization. The PL and PLE spectra obtained show that there are three optical centers, of which the first is originated from the F⁺ centers in AAMs, the second is correlated with the oxalic impurities incorporated in the AAMs, and the third is associated with the excess aluminum ions in the membrane.     

Invited Review Electronic properties of nanostructures defined in Ga[Al]As heterostructures by local oxidation

Semiconductor nanostructures are fabricated by local oxidation of Ga[Al]As heterostructures with an atomic force microscope (AFM). The GaAs surface is locally oxidized by applying a bias between the substrate and a conductive AFM tip in a humidity-controlled environment. For high-quality two-dimensional electron gases (2DEGS) located close enough to the sample surface the electrons get depleted below the oxidized regions. This way the plane of a 2DEG can be cut into various conductive areas which are laterally insulated from each other. The realization of several high-quality semiconductor nanostructures is demonstrated. I. Quantum wires are fabricated with smooth and steep potential. II. Quantum dots tuned by in-plane gate electrodes can be operated in the regime, where electrons tunnel sequentially through individual quantum levels. III. Antidot superlattices with high-precision lattice parameters display characteristic features of classical and quantum transport.     

高迁移率非晶铟镓锌氧化物薄膜晶体管的制备与特性研究

由于铟镓锌氧化物(IGZO) 薄膜具有高迁移率和高透过率的特点, 它作为有源层被广泛的应用于薄膜晶体管(TFT). 本文利用磁控溅射方法制备了TFT的有源层IGZO和源漏电极, 用简单低成本的掩膜法控制沟道的尺寸, 制备了具有高迁移率、底栅结构的n型非晶铟镓锌氧化物薄膜晶体管 (IGZO-TFT). 利用X 射线衍射仪(XRD) 和紫外可见光分光光度计分别测试了IGZO薄膜的衍射图谱和透过率图谱, 研究了IGZO薄膜的结构和光学特性. 通过测试IGZO-TFT的输出特性和转移特性曲线, 讨论了IGZO有源层厚度对IGZO-TFT特性的影响. 制备的IGZO-TFT器件的场效应迁移率高达15.6 cm²·V^-1·s^-1, 开关比高于10⁷. 关键词： 非晶铟镓锌氧化物 薄膜晶体管 有源层     

Effect of electron irradiation on the oxidation of indium

The oxidation kinetics of indium is studied for two cases, namely, during continuous electron irradiation (E _p = 1800 eV) and without electron irradiation, as a function of the time of exposure to an oxygen medium at a partial oxygen pressure of 10⁻⁴ Pa and room temperature. The initial oxygen exposure was 50 L. The kinetic curves recorded upon continuous electron irradiation have two inflection points, and they can be attributed to the following three states of oxidation: physical adsorption, chemisorption with the formation of a nonstoichiometric oxide layer, and the growth of a homogeneous oxide layer. Only the first inflection point is observed during oxidation without electron irradiation, and further exposure does not lead to the second inflection point within the experimental time.     

Antimony thin-film transport properties and size effect

Antimony thin films were vacuum deposited on glass substrates at room temperature. X-ray structural studies were performed. The thickness dependence of both the de electrical resistivity and the Hall coefficient were earried out at room temperature over a thickness range from 29 nm to 216 nm. The type of conduction, the concentration and the mobility of charge carriers were revealed.Analysis incorporating the electrical resistivity and the Hall effect data has led to the determination of the specular and non-specular size-effect parameters. Parameters such as the bulk resistivity ( ₀), bulk mean free path ( ₀), grain-boundary transmission coefficient (t), external surface parameters (U), surface scattering factor (p) and grain-boundary parameter (V), were all evaluated without using any adjusting parameters.Beside the background contribution to the film resistivity, an estimation of the contribution of the surface and grain-boundary to the film resistivity was also carried out.     

Electrical properties of indium implanted silicon

Electrical conductivity and Hall effect were measured from 100° to 278°K as a function of layer removal to determine the indium ionization energy and the presence of compensating centers resulting from the implantation of indium into silicon. The implants were fully annealed to reduce the influence of radiation damage. For comparison, similar measurements were performed on silicon shallow diffused with indium. Differential analysis methods were used to compute carrier concentration, mobility, and resistivity for the stripped layers. In addition, Hall measurements were performed on silicon uniformly doped with indium. In all three cases an indium energy level of 160 meV was observed. Mobility plots versus temperature were also consistent. However, significant compensation effects were noticed in the implants.     

The photo-electric properties of indium antimonide

A change of resistance or the formation of a voltage in mono- or polycrystalline samples of InSb due to illumination has been observed, the magnitudes of which increase with decreasing temperatures. It is demonstrated that this is a photo-conductive effect, arising in the volume of the sample or at barriers due to non-homogeneities, and a photo-voltaic effect. The spectral curves were measured with long-wave limits _1/2=5.8 at –155 °C, _1/2=6.7 at –42 °C.It is shown that these phenomena are caused by the transition of electrons from the valence-bond band to the conduction band under the influence of photons. The width of the band of forbidden energy values below room temperature was found to be E _G=0.24–2.4×10^–4T(eV).It is our pleasant obligation to thank Prof. Dr. L. Zachoval for permission to perform certain parts of this work in the Physics Institute of Charles' University, and Ing. A. Vaek and Dr. J. Plíva for valuable advice in carrying out the measurements and Ing. K. mirous for preparation of the samples.     

Surface-modification of indium tin oxide nanoparticles with titanium dioxide by a nonaqueous process and its photocatalytic properties

Indium tin oxide nanoparticles prepared by co-precipitation were re-dispersed in benzyl alcohol and modified successfully with titanium dioxide using titanium tetrachloride as precursor. The morphologies and the re-dispersing processes of both the initial and modified indium tin oxide nanoparticles were investigated, respectively. The photocatalytic properties of the modified nanoparticles were compared with commercial P25 photocatalyst. It was found that (i) the average diameter of the initial indium tin oxide nanoparticles was 10.7 nm and that of the surface-modified nanoparticles was 14.5 nm; (ii) the optimal ultrasonication time was 10.0 min and 8.0 min for the initial and surface-modified ITO nanoparticles, respectively; (iii) the modified particles possessed a higher photocatalytic activity than commercial P25 photocatalyst in the photodegradation of rhodamine B in aqueous medium at pH 5.00; (iv) the pH of the medium markedly influences the photodegradation efficiency.