Effect of Heat and Plasma Treatments on the Photoluminescence of Zinc-Oxide Films

The structure and electrical properties of ZnO films and the effect of annealing in a hydrogen-plasma atmosphere on the photoluminescence spectra of the films are studied. Short-term plasma treatment in a hydrogen atmosphere improves the electrical properties and brings about the appearance of an intense near-band-edge photoluminescence band. The heavy dependence of the intensity and spectral shape of nearband- edge photoluminescence on the conditions of preliminary annealing is observed. It is shown that the photoluminescence spectrum consists of several contributions. The effect of an ultraviolet-radiation-induced increase in the photoluminescence intensity is observed. The effect is reversible: the photoluminescence signal is intensified after exposure to ultraviolet radiation and reduced to the initial intensity upon keeping the samples in the dark. The nature of experimentally observed metastable shallow donors is discussed.     

On the nature of the defect passivation in polycrystalline silicon by hydrogen and oxygen plasma treatments

The effect of hydrogen and oxygen plasmas on the properties of polycrystalline silicon films and thin-film transistors are investigated. The results clearly demonstrate that an oxygen plasma does not passivate grain boundary defects. However, an oxygen plasma treatment at 300 K still improves the electrical properties of thin-film transistors.<>     

Effect of thermal annealing and exposure to oxygen plasma on the properties of TiO2-Si structures

The effect of thermal annealing and exposure to oxygen plasma on the phase composition, structure, and microprofile of titanium-dioxide films deposited by high-frequency magnetron sputtering on silicon substrates is studied. The influence exerted by processing modes on the capacitance-voltage and conductance-voltage characteristics of Me-TiO₂-Si-Me structures and on the density of surface states at the semiconductor-insulator interface is examined. It is shown that TiO₂ films are amorphous upon their fabrication. Upon the annealing of films at 500°C in an argon atmosphere, crystallites of anatase and rutile appear in the amorphous matrix. The treatment of a titanium-dioxide film in oxygen plasma gives rise to rutile crystallites with new crystallographic planes. As a result of annealing at 750°C, the anatase phase disappears and the film becomes polycrystalline, containing only rutile crystallites. The capacitance of Me-TiO₂-Si-Me structures in the accumulation mode reaches the maximum value upon annealing at 750°C, which is due to the transformation of titanium dioxide to the rutile phase. The specific capacitance is 5.9 × 10^?2 F/cm³. The decrease in the capacitance of the structures and in the amount of fixed charge in the insulator upon exposure to oxygen plasma is due to the diffusion of oxygen atoms across the titanium-dioxide layer to give a SiO₂ film at the TiO₂-Si interface. As a result of the annealing and treatment of a titanium-dioxide film in oxygen plasma, the energy density of surface states decreases by more than an order of magnitude as compared with the unannealed samples.     

Deposition and doping of CdS/CdTe thin film solar cells

1% oxygen is incorporated into both CdS and CdTe layers through RF sputtering of CdS/CdTe thin film solar cells. The optical and electrical parameters of the oxygenated and O₂-free devices are compared after CdCl₂ treatment and annealing in ambient Ar and/or air. The effects of ambient annealing on the electrical and optical properties of the films are investigated using current-voltage characterization, field emission scanning electron microscopy, X-ray diffraction, and optical transmission spectroscopy. The 1% oxygen content can slightly increase the grain size while the crystallinity does not change. Annealing in ambient Ar can increase the transmission rate of the oxygenated devices.     

Bi_(1.5)Mg_(1.0)Nb_(1.5)O_7薄膜的介电损耗机理研究

采用射频磁控溅射法在Al2O3基片上沉积了铌酸铋镁(Bi1.5Mg1.0Nb1.5O7,BMN)薄膜,研究了不同退火条件下BMN薄膜的介电损耗机理。结果表明,充分的退火能够减小氧空位缺陷密度,并降低介电损耗。氧气气氛下退火能够有效补偿BMN薄膜中的氧空位,使得介电损耗进一步降低。这说明氧空位导致的带电缺陷损耗是BMN薄膜材料主要的介电损耗机制。此外,BMN薄膜中也存在晶界损耗机制。     

Effect of annealing on the morphology and optoelectrical characteristics of ZnO thin films grown by plasma-assisted molecular beam epitaxy

The dependence of characteristics of plasma-assisted molecular beam epitaxy-grown ZnO thin films on different postgrowth annealing conditions was investigated. It was found that, under oxygen atmosphere, annealing temperature can profoundly affect the morphological, electrical, and optical properties of ZnO thin films. In particular, the surface morphology changed from a relatively smooth surface before annealing to various island morphologies after annealing above 800°C for samples grown directly on sapphire without a buffer layer. It is speculated that intrinsic stress due to lattice mismatch drives the island formation and the high temperature provides the energy needed for this surface rearrangement. Single-field Hall-effect measurement showed that the carrier concentration improved by an order of magnitude and the mobility increased from about 30 cm²/Vs to ∼70 cm²/Vs by annealing at 750°C. Variable-field Hall effect shows that a model with two carriers, one a degenerate low-mobility electron and the other a higher mobility non-degenerate electron, is needed to explain the transport properties of the thin film. Analysis indicates that annealing at 750°C decreased the carrier concentration and increased the mobility for the high-mobility carrier. Annealing also led to a significant improvement in photoluminescence, with temperatures of ∼750–850°C yielding the best results.     

ZnO Thin Films with Hole Conduction Produced by N+ Ion Implantation and Oxygen-Radical Annealing

Hole conduction is produced in ZnO thin films by N⁺ ion implantation and annealing in an oxygen-radical atmosphere. It is established that oxygen radicals are necessary for hole conduction to appear. The implantation and annealing are found to change not only the electrical behavior of the film but also its photoluminescence spectrum, creating UV and visible bands.     

Grain Boundary Carrier Scattering in ZnO Thin Films: a Study by Temperature-Dependent Charge Carrier Transport Measurements

In the present investigation, the effects of annealing in oxygen atmosphere on the electrical and optical properties of pulsed direct-current (DC) magnetron-sputtered ZnO thin films have been studied. With annealing, the electrical conductivity was found to increase from 2.3 S cm to 123 S cm. The optical transparency was also found to improve from 83% to 90%. The improvement in the electrical properties with annealing is attributed to the reduction of the grain boundary potential from 34 meV to 8 meV. X-ray photoelectron spectroscopy (XPS) measurements revealed oxygen deficiency in as-deposited films, whereas adequate incorporation of oxygen was observed in the annealed films. Ultraviolet photoelectron spectroscopy (UPS) measurements showed a shift of +0.8 eV in the Fermi level with annealing. This shift indicates significant changes in the electrical conductivity with annealing, which is due to an increase in the carrier concentration.     

The role of grain-boundary on the hydrogen-induced degradation inthin-film ferroelectric capacitors

The electrical properties of thin-film ferroelectric capacitors are known to degrade severely when exposed to hydrogen. In this study, we directly measured the effects of the grain boundary on the hydrogen-induced degradation in ferroelectric Pb(Zr, Ti)O₃ (PZT) thin films by the location of the top Pt electrode either inside the grains or at the grain boundary. A strong relationship between the grain boundary and the electrical properties of ferroelectric capacitors as a result of hydrogen annealing was found. The degradation of the electrical properties in thin-film ferroelectric capacitors after hydrogen annealing is mainly due to the presence of the grain boundary in the ferroelectric thin film     

Synthesis of thin p-type rutile films

The structure and electrical and optical properties of heterostructures formed on the surface of single-crystal silicon wafers as a result of the heat treatment and pulsed photon treatment of Ti films in oxygen, air, and nitrogen are investigated. It is shown that a TiO₂/Ti₅Si₃/p-Si heterostructure is formed upon heat treatment in air, whereas a TiO₂/TiSi₂/p-Si heterostructure is formed upon photon treatment. It is established that rutile films with pronounced n-type conductivity are formed as a result of the heat treatment of Ni-doped Ti films in oxygen. Rutile films with p-type conductivity are formed upon the thermal annealing of Ti films in air with subsequent photon treatment in nitrogen.     

Specific Features and Nature of the 890 nm Photoluminescence Band Detected in SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films after Low-Temperature Annealing

A band with a peak at 890 nm is detected in the photoluminescence spectra of SiO _x (x ≈ 1.3) films deposited by thermal evaporation of SiO and annealed in air at 650–1150°C. The 890-nm band appears after low-temperature (∼650°C) annealing and exhibits a number of features: (i) as the annealing temperature is elevated to 1150°C, the position of the band peak remains unchanged, whereas the intensity increases by two orders of magnitude; (ii) the effects of the annealing atmosphere (air, vacuum) and the excitation wavelength and power density on the intensity of the 890-nm band differ from the corresponding effects on the well-known bands observable in the ranges 600–650 and 700–800 nm; and (iii) the photoluminescence decay is first fast and then much slower, with corresponding lifetimes of ∼9 and ∼70 μs. The observed features are inconsistent with the interpretation of photoluminescence observed in SiO _x so far. Specifically, the earlier observed photoluminescence was attributed to transitions between the band and defect states in the matrix and between the states of band tails, transitions inside Si nanoclusters, and intraion transitions in rare-earth impurity ions. Therefore, we consider here the possibility of attributing the 890-nm band to transitions in local centers formed by silicon ions twofold- and/or threefold-coordinated with oxygen; i.e., we attempt to interpret the 890-nm band in the same manner as was done for luminescence in SiO₂ glasses and films slightly deficient in oxygen.     

Structure and electrical properties of polycrystalline SiGe films grown by molecular beam deposition

The structural and electrical properties of polycrystalline Si_0.5Ge_0.5 films 150 nm thick grown by molecular beam deposition at temperatures of 200–550°C on silicon substrates coated with amorphous layers of silicon oxynitride were studied. It is shown that the films consist of a mixture of amorphous and polycrystalline phases. The amorphous phase fraction decreases from ～50% in films deposited at 200°C to zero in films grown at 550°C. Subsequent 1-h annealing at a temperature of 550°C results in complete solid-phase crystallization of all films. The electron transport of charge carriers in polycrystalline films occurs by the thermally activated mechanism associated with the energy barrier of ～0.2 eV at grain boundaries. Barrier lowering upon additional annealing of SiGe films correlates with an increase in the average grain size.     

Grain boundary mediated leakage current in polycrystalline HfO2 films

In this work, we combine conductive atomic force microscopy (CAFM) and first principles calculations to investigate leakage current in thin polycrystalline HfO₂ films. A clear correlation between the presence of grain boundaries and increased leakage current through the film is demonstrated. The effect is a result of a number of related factors, including local reduction in the oxide film thickness near grain boundaries, the intrinsic electronic properties of grain boundaries which enhance direct tunnelling relative to the bulk, and segregation of oxygen vacancy defects which increase trap assisted tunnelling currents. These results highlight the important role of grain boundaries in determining the electrical properties of polycrystalline HfO₂ films with relevance to applications in advanced logic and memory devices.     

Preparation and characterization of cubic lattice ZnS：Na Films with （111） preferred orientation

ZnS：Na thin films with （111） preferred orientation were deposited on glass substrates by vacuum evaporation method. The as-prepared films were annealed in flowing argon at 400--500 ℃ to improve the film crystallinity and electrically activate the dopants. The structural, optical and electrical properties of ZnS：Na films are investigated by X-ray diffrac- tion （XRD）, photoluminescence （PL）, optical transmittance measurements and the four-point probe method. Results show that the as-prepared ZnS：Na films are amorphous, and exhibit （111） preferred orientation after annealing at 400 --500 ℃. The PL emissions at 414 nm and 439 nm are enhanced due to the increase of the intrinsic defects induced by the thermal annealing. However, all the samoles exhibit high resistivitv due to the heavy self-compensation.     

Structural, electrical and optical properties of zinc oxide produced by oxidation of zinc thin films

We have investigated the effects of oxidation temperature on the physical properties of polycrystalline zinc oxide thin films. Zinc thin films are oxidized at different temperatures in air. We have found that increasing the oxidation temperature deteriorates the preferred c-axis orientation. Also, increasing the oxidation temperature enlarges the crystal size and increases the number of needle-shaped crystals on the surface of the ZnO samples. By increasing the oxidation temperature, more than zinc melting point, tensile stresses start to build up in the films. Also by increasing temperature, sheet resistance of the films decreases, while photoluminescence intensity ratio (green to orange) increases. Increasing the oxidation temperature reduces the transparency of the films, too. It is proposed that either an increase in the number of oxygen vacancies or a decrease in the volume of grain boundaries, is responsible for the observed behavior of the films at higher oxidation temperatures.     

表面覆盖退火对ZnO薄膜光学性质的影响

研究了暴露在空气中退火和表面覆盖蓝宝石基板退火对MOCVD生长的ZnO薄膜光学性质的影响.研究发现,暴露在空气中退火虽可以去除薄膜中的氢杂质,并在低温光致发光(PL)谱中观察到与氢相关的束缚激子峰消失,但是退火后样品室温PL谱中可观察到很强的可见光发射,表明样品中引入了大量的深能级,样品的自由激子发光没有增强.而表面覆盖蓝宝石基板退火的样品,有效去除了氢杂质,但没有观察到可见光发射,说明表面覆盖蓝宝石基板退火可以有效地保护ZnO表面不分解,不生成深能级中心.由于激子束缚中心的减少,表面覆盖退火样品的自由激子发射大大增强.     

Effect of annealing in oxygen radicals on luminescence and electrical conductivity of ZnO:N films

It is shown that the introduction of a nitrogen acceptor impurity when growing zinc oxide films can result in the formation of hole conduction only after annealing in atomic oxygen vapor. Annealing affects not only electrical properties but also the luminescence of ZnO:N. The bands in the photoluminescence spectrum, which are related to nitrogen, appear in the ultraviolet and visible regions.     

Electrical and optical properties of ITO and ITO:Zr transparent conducting films

ITO and ITO:Zr films were deposited on glass substrates by magnetron sputtering. Electrical and optical properties of the films at different experiment parameters such as substrate temperature, oxygen flow rate and annealing temperature were contrastively studied. The increase in substrate temperature remarkably improves the electrical and optical properties of the films. ITO:Zr films show better quality at low substrate temperature. The excessive oxygen can worsen the optical properties of the films. Better optical–electrical properties of the films can be achieved after the proper annealing treatment. Obvious Burstin–Moss effect can be revealed by transmittance spectra with different parameters, and the direct transition models show the change of optical band gap. ITO:Zr films prepared by co-sputtering show better optical–electrical properties than ITO films.     

Crystallization and Transport Properties of Amorphous Cr-Si Thin Film Thermoelectrics

We studied the thermoelectric properties, crystallization, and stability of amorphous and nanocrystalline states in Cr-Si composite films. Amorphous films, prepared by magnetron sputtering, were transformed into the nanocrystalline state by annealing with in situ thermopower and electrical resistivity measurements. We have found that the amorphous state is stable in these film composites to about 550 K. Prior to crystallization, the amorphous films undergo a structural relaxation, detected by peculiarities in the temperature dependences of the transport properties, but not visible in x-ray or electron diffraction. The magnitude and temperature dependences of electrical conductivity and thermopower indicate that electron transport in the amorphous films is through extended states. The amorphous films are crystallized at annealing temperatures above 550 K into a nanocrystalline composite with an average grain size of 10–20 nm.     

Influence of substrate temperature and post deposition annealing on the properties of vacuum deposited ZnSe thin films

The effects of substrate temperature and post deposition annealing on the structural, optical and electrical properties of vacuum deposited ZnSe thin films are presented here. The chemical composition of the films varied drastically with substrate temperature which in turn caused changes in various properties of the films. The grain size of the films increased with substrate temperature and also after annealing. The electrical properties of the films were found to be varying as a function of chemical composition and grain size.