Showing papers on "Thin film published in 1995"
TL;DR: In this paper, the interpenetrating network formed from a phase-segregated mixture of two semiconducting polymers is shown to provide both the spatially distributed interfaces necessary for efficient charge photo-generation, and the means for separately collecting the electrons and holes.
Abstract: THE photovoltaic effect involves the production of electrons and holes in a semiconductor device under illumination, and their subsequent collection at opposite electrodes. In many inorganic semiconductors, photon absorption produces free electrons and holes directly1. But in molecular semiconductors, absorption creates electrona¤-hole pairs (excitons) which are bound at room temperature2, so that charge collection requires their dissociation. Exciton dissociation is known to be efficient at interfaces between materials with different electron affinities and ionization potentials, where the electron is accepted by the material with larger electron affinity and the hole by the material with lower ionization potential3. A two-layer diode structure can thus be used, in which excitons generated in either layer diffuse towards the interface between the layers. However, the exciton diffusion range is typically at least a factor of 10 smaller than the optical absorption depth, thus limiting the efficiency of charge collection3. Here we show that the interpenetrating network formed from a phase-segregated mixture of two semiconducting polymers provides both the spatially distributed interfaces necessary for efficient charge photo-generation, and the means for separately collecting the electrons and holes. Devices using thin films of these polymer mixtures show promise for large-area photodetectors.
3,165 citations
TL;DR: In this article, the authors describe the preparation and characterization of thin-film capacitors using ferroelectric materials from a large family of layered perovskite oxides, exemplified by SrBi2Ta2O9, SRBi2NbTaO9 and SrBi4Ta4O15.
Abstract: A SIGNIFICANT fraction of the computer memory industry is at present involved in the manufacture of non-volatile memory devices1—that is, devices which retain information when power is interrupted. For such applications (and also for volatile memories), the use of capacitors constructed from ferroelectric thin films has stimulated much interest1. In such structures, information is stored in the polarization state of the ferroelectric material itself, which should in principle lead to lower power requirements, faster access time and potentially lower cost1. But the use of ferroelectrics is not without problems; the memories constructed to date have generally suffered from poor retention of stored information and degradation of performance ('fatigue') with use1–3. Here we describe the preparation and characterization of thin-film capacitors using ferroelectric materials from a large family of layered perovskite oxides, exemplified by SrBi2Ta2O9, SrBi2NbTaO9 and SrBi4Ta4O15. The structural flexibility of these materials allows their properties to be tailored so that many of the problems associated with previous ferroelectric memories are avoided. In particular, our capacitors do not show significant fatigue after 1012 switching cycles, and they exhibit good retention characteristics and low leakage currents even with films less than 100 nm thick.
2,378 citations
TL;DR: Light-emitting devices based on conjugated polymers have been fabricated that operate by the proposed electrochemical oxidation-reduction mechanism and blue, green, and orange emission have been obtained with turn-on voltages close to the band gap of the emissive material.
Abstract: A device configuration for light emission from electroactive polymers is described. In these light-emitting electrochemical cells, a p-n junction diode is created in situ through simultaneous p-type and n-type electrochemical doping on opposite sides of a thin film of conjugated polymer that contains added electrolyte to provide the necessary counterions for doping. Light-emitting devices based on conjugated polymers have been fabricated that operate by the proposed electrochemical oxidation-reduction mechanism. Blue, green, and orange emission have been obtained with turn-on voltages close to the band gap of the emissive material.
1,559 citations
TL;DR: In this paper, an understanding of the molecular mechanisms of tribology in thin films and at surfaces has been presented, which is of fundamental importance in many pure and applied sciences, such as computer simulations.
Abstract: Friction, wear and lubrication between materials in contact are of fundamental importance in many pure and applied sciences. Owing to the development of experimental and computer-simulation techniques for studying these phenomena at the atomic scale, an understanding is beginning to emerge of the molecular mechanisms of tribology in thin films and at surfaces.
1,393 citations
TL;DR: The electroluminescence of CdSe nanocrystallites (quantum dots) incorporated into thin films (1000 A) of polyvinyl carbazole (PVK) and an oxadiazole derivative (t‐Bu‐PBD) and sandwiched between ITO and Al electrodes was studied in this article.
Abstract: Electroluminescence is obtained from nearly monodisperse CdSe nanocrystallites (quantum dots) incorporated into thin films (1000 A) of polyvinylcarbazole (PVK) and an oxadiazole derivative (t‐Bu‐PBD) and sandwiched between ITO and Al electrodes. The electroluminescence and photoluminescence spectra (bandwidths ≤40 nm) are nearly identical at room temperature and are tunable from ∼530 to ∼650 nm by varying the size of the dots. Voltage studies at 77 K indicate that while only the dots electroluminesce at the lower voltages, both the dots and the PVK matrix electroluminesce at higher applied voltages. Variable temperature studies indicate that the electroluminescence efficiency increases substantially as the films are cooled down to cryogenic temperatures.
1,032 citations
TL;DR: The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.
Abstract: A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO(3), Bi(2)O(3), CaO, CuO, PbO, SrCO(3), and Y(2)O(3) were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.
965 citations
TL;DR: In this paper, the growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15-40 nm and about 2 μm long are reviewed and discussed.
Abstract: The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 μm long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic and optical devices.
638 citations
TL;DR: In this paper, surface tension effects can induce the growth of uniform, thin metal oxide films on the outside of carbon nanotubes, along with oxide fillings in the internal cavities and thin oxide layers between the concentric shells of the tubes.
Abstract: SEVERAL techniques have been developed recently for fabricating nanocomposite structures by filling1–3 carbon nanotubes4,5. Here we show that surface-tension effects can induce the growth of uniform, thin metal oxide filmsa€"sometimes only a monolayer thicka€"on the outside of nanotubes, along with oxide fillings in the internal cavities and thin oxide layers between the concentric shells of the tubes. We report the preparation of such nanotube–oxide composites by annealing a mixture of partially oxidized nanotubes and V2O5 powder in air above the melting point of the oxide. The external coatings of the tubes are crystalline sheets of the V2O5 layer-like structure, which grow with the c axis parallel to that of the nanotube layers. Intercalation of the oxide occurs where there are missing shells in the nanotubes. We also show that the nanotubes can be partially removed by oxidation, leaving behind layered oxide fibres. Given the importance of vanadium oxides as catalysts and functional ceramics, this role of nanotubes as removable templates might lead to useful new kinds of nanostructured materials.
624 citations
TL;DR: In this paper, N-channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element, showing on-off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V
Abstract: N‐channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element. Measurements on C60 thin films in ultrahigh vacuum show on‐off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V s.
526 citations
TL;DR: In this article, a model that explains the yield stress and hardness enhancements that have been observed in superlattice thin films was presented, where the stress required for dislocations to glide across layers with different shear moduli was calculated using an expression that accounts for core effects and all interfaces in trapezoidal or sawtooth composition modulations.
Abstract: A model is presented that explains the yield stress and hardness enhancements that have been observed in superlattice thin films. The stress required for dislocations to glide across layers with different shear moduli was calculated using an expression that accounts for core effects and all interfaces in trapezoidal or sawtooth composition modulations. The predicted strength/hardness enhancement increased with increasing superlattice period Λ, before reaching a saturation value that depended on interface widths. A second mechanism, where dislocations glide within individual layers, was important at large Λ and gave a decrease in strength/hardness with increasing Λ. The combination of these two mechanisms gives a strength/hardness maximum versus Λ in good quantitative agreement with experimental results for nitride and metal superlattices. The results indicate that superlattice strength/hardness depends strongly on interface widths and the difference in shear moduli of the two components for Λ values below the maximum, and on the average shear modulus for larger Λ.
491 citations
TL;DR: In this article, thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition.
Abstract: Thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition. The films show a high Vickers hardness of 5000 kg/mm2 and elastic modulus of ≳500 GPa, and they are resistant against oxidation in air up to ≥800 °C. The theoretical background of these unusual properties are briefly discussed and practical rules suggested according to which similar properties should be expected for composites of other ternary systems.
TL;DR: In this article, a binary reaction for Al2O3 chemical vapor deposition (2Al (CH3)3 + 3H2O → Al 2O3 + 6CH4) was separated into two half-reactions: (A) AlOH + Al(CH 3)3 → Al-O-Al(CH 4)2 + 2H 2O + 2CH4; (B) Al O-Al (H 3)2+ 3H 2
TL;DR: In this article, a Ti:sapphire laser was used to ablate holes with a diameter of 300 nm and a depth of 52 nm to produce very small features in materials.
TL;DR: In this article, the properties of Ga2O3 thin films deposited by electron-beam evaporation from a high-purity single-crystal Gd3Ga5O12 source are reported.
Abstract: Properties of Ga2O3 thin films deposited by electron‐beam evaporation from a high‐purity single‐crystal Gd3Ga5O12 source are reported. As‐deposited Ga2O3 films are amorphous, stoichiometric, and homogeneous. Excellent uniformity in thickness and refractive index was obtained over a 2 in. wafer. The films maintain their integrity during annealing up to 800 and 1200 °C on GaAs and Si substrates, respectively. Optical properties including refractive index (n=1.84–1.88 at 980 nm wavelength) and band gap (4.4 eV) are close or identical, respectively, to Ga2O3 bulk properties. Reflectivities as low as 10−5 for Ga2O3/GaAs structures and a small absorption coefficient (≊100 cm−1 at 980 nm) were measured. Dielectric properties include a static dielectric constant between 9.9 and 10.2, which is identical to bulk Ga2O3, and electric breakdown fields up to 3.6 MV/cm. The Ga2O3/GaAs interface demonstrated a significantly higher photoluminescence intensity and thus a lower surface recombination velocity as compared to ...
TL;DR: Ferroelectric SrBi2Ta2O9 thin films were synthesized on Pt/Ti/SiO2/Si substrates using a solution deposition process, and structural and electrical properties were investigated as discussed by the authors.
Abstract: Ferroelectric SrBi2Ta2O9 thin films were synthesized on Pt/Ti/SiO2/Si substrates using a solution deposition process, and structural and electrical properties were investigated. The spin‐on films crystallized during firing above 700 °C. The films showed high diffraction peaks of (105) and (200), while little peaks from (00l) planes were observed. Good ferroelectric properties were obtained for a 280 nm thick film; Pr and Ec were 10.0 μC/cm2 and 38 kV/cm, respectively. Fatigue endurance was excellent; the hysteresis loop does not change up to 109 switching cycles. These properties are very attractive for nonvolatile memory application.
TL;DR: In this article, the anatase modification of TiO2 shows properties quite different from those of the extensively studied and used rutile phase, such as high electron mobility and the low density of trapping or compensating centers are considered to have contributed to this good response.
Abstract: The anatase modification of TiO2 shows properties quite different from those of the extensively studied and used rutile phase. We have investigated the chemi-resistive behavior of anatase TiO2 thin films exposed to oxidizing and reducing gases (O2, H2 and ethanol) in the temperature range between 300 and 400 °C. The undoped anatase films demonstrate significant and rapid response to ethanol as well as an appreciable response to hydrogen. The high electron mobility and the low density of trapping or compensating centers are considered to have contributed to this good response. Doping the anatase thin films with Sr, Ce, Y and Tb makes then insensitive to hydrogen, but still sensitive to ethanol. The modification of the sensitivity and its dynamics by dopants have been measured and analyzed.
TL;DR: In this article, the topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations.
Abstract: The atomically ultrasmooth surfaces with atomic steps of sapphire substrates were obtained by annealing in air at temperatures between 1000 and 1400 °C. The terrace width and atomic step height of the ultrasmooth surfaces were controlled on an atomic scale by changing the annealing conditions and the crystallographic surface of substrates. The obtained ultrasmooth surface was stable in air. The topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations.
Patent•
06 Jun 1995TL;DR: In this article, the authors proposed a method and apparatus for depositing a film on a substrate by plasma-enhanced chemical vapor deposition at temperatures substantially lower than conventional thermal CVD temperatures, which includes placing a substrate within a reaction chamber and exciting a first gas upstream of the substrate to generate activated radicals of the first gas.
Abstract: A method and apparatus for depositing a film on a substrate by plasma-enhanced chemical vapor deposition at temperatures substantially lower than conventional thermal CVD temperatures comprises placing a substrate within a reaction chamber and exciting a first gas upstream of the substrate to generate activated radicals of the first gas. The substrate is rotated within the deposition chamber to create a pumping action which draws the gas mixture of first gas radicals to the substrate surface. A second gas is supplied proximate the substrate to mix with the activated radicals of the first gas and the mixture produces a surface reaction at the substrate to deposit a film. The pumping action draws the gas mixture down to the substrate surface in a laminar flow to reduce recirculation and radical recombination such that a sufficient amount of radicals are available at the substrate surface to take part in the surface reaction. Another method utilizes a gas-dispersing showerhead that is biased with RF energy to form an electrode which generates activated radicals and ions in a concentrated plasma close to the substrate surface. The activated plasma gas radicals and ions utilized in the invention contribute energy to the surface reaction such that the film may be deposited at a substantially lower deposition temperature that is necessary for traditional thermal CVD techniques. Furthermore, the activation of these species reduces the temperature needed to complete the surface reaction. The method is particularly useful in depositing titanium-containing films at low temperatures.
Patent•
15 Jun 1995TL;DR: In this paper, a high performance thin-film semiconductor device using a low temperature process in which it is possible to use low price glass substrates has been fabricated by forming a silicon film at less than 450° C, and, after crystallization, keeping the maximum processing temperature at or below 350° C.
Abstract: In order to fabricate a high performance thin film semiconductor device using a low temperature process in which it is possible to use low price glass substrates, a thin film semiconductor device has been fabricated by forming a silicon film at less than 450° C, and, after crystallization, keeping the maximum processing temperature at or below 350° C In applying the present invention to the fabrication of an active matrix liquid crystal display, it is possible to both easily and reliably fabricate a large, high-quality liquid crystal display Additionally, in applying the present invention to the fabrication of other electronic circuits as well, it is possible to both easily and reliably fabricate high-quality electronic circuits
TL;DR: In this article, a molecular-level manipulation of conjugated polyions has been successfully utilized to fabricate ultrathin multilayer films and multi-layer heterostructures, using a process involving the alternate spontaneous adsorption of oppositely charged polymers from dilute aqueous solutions.
Abstract: The layer-by-layer molecular-level manipulation of conjugated polyions has been successfully utilized to fabricate ultrathin multilayer films and multilayer heterostructures. Through a process involving the alternate spontaneous adsorption of oppositely charged polymers from dilute aqueous solutions, multilayer thin films were fabricated from a variety of different bilayer combinations including conjugated/nonconjugated polyion bilayers, conjugated/conjugated polyion bilayers, and precursor polymer/conjugated polyion bilayers. UV-vis absorbance measurements revealed that in all cases the bilayer deposition process was linear and highly reproducible from layer to layer. Kinetic studies showed that the equilibrium adsorption of a polyion layer is reached within about 10 min and the process can be carried out onto different substrate surfaces. The typical bilayer thickness ranges from approximately 10 to 25 A and can be readily controlled by variations in such parameters as solution concentration, pH, doping level, and ionic strength.
TL;DR: The preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive magnetron sputter deposition on amorphous SiO2 at 350°C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N) as mentioned in this paper.
Abstract: The preferred orientation of polycrystalline TiN films grown by ultrahigh‐vacuum reactive‐magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N). All samples were slightly over‐stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from ≂0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240...
TL;DR: In this paper, the hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients.
Abstract: Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H{sub 2}/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 run. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. Results show that the hardness, elastic modulus, and scratch resistance of the 20 and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.
TL;DR: In this paper, the insertion reaction of several different intercalation materials, amorphous V{sub 2}O{sub 5}, ammorphous LiMn{sub 1}O {sub 4}, and crystalline LiMmn{ sub 2 O{sub 4} films, have been investigated using the completed cathode/electrolyte/lithium thin-film battery.
TL;DR: In this article, the synthesis of metal-free and dihydroxysilicon derivatives of tetrakis[4',5'-bisdecoxy)benzo-18-crown-6]phthalocyanine is described.
Abstract: The synthesis of the metal-free and the dihydroxysilicon derivatives of tetrakis[4',5'-bis(decoxy)benzo-18-crown-6]phthalocyanine is described. The metal-free phthalocyanine is liquid crystalline and exhibits a crystalline phase to mesophase transition at 148 degrees C. The structures of the crystalline phase and the mesophase are determined by X-ray measurements. The metal-free compound strongly aggregates in chloroform solution to form a gel. Electron micrographs show that this gel contains a network of fibers, each of which is built up of parallel strands of supermolecules having the thickness of one molecule and a length of several micrometers. The strands are formed by a process of self-assembly involving up to 10(4) molecules. They can be considered as being molecular cables, containing a central electron wire, four ion channels, and a surrounding insulating hydrocarbon mantle. The silicon derivative contains two axial hydroxy groups which prevent the molecule from aggregating. This compound is not liquid crystalline. It forms a stable monolayer at the air-water interface. In this layer, the phthalocyanine planes are oriented parallel to the water surface. The monolayers can be transferred onto glass substrates by a Y-type deposition. The resulting Langmuir-Blodgett film is built up of bilayers containing slipped face-to-face phthalocyanine dimers. The monolayer is capable of binding alkali metal ions from the subphase, as is concluded from surface area-surface pressure isotherms. The binding constant for potassium ions has been determined by analyzing the isotherms as a function of the concentration of this metal ion. The dihydroxysilicon phthalocyanine can be polymerized to form a polysiloxane.
TL;DR: In this article, a method for fabricating low-resistivity molybdenum films on soda-lime glass substrates with good adhesion was described, where 1-μm-thick films sputtered at low argon pressure were found to have low resistivity (10−15 μΩ cm), were under compressive stress, and suffered from poor adhesion.
TL;DR: A method for the fabrication of micrometers-and submicrometer-sized polymeric light-emitting diodes is presented, which have a variety of applications and are suitable for subwavelength, near-field optical microscopy.
Abstract: A method for the fabrication of micrometer-and submicrometer-sized polymeric light-emitting diodes is presented. Such diodes have a variety of applications. Light sources of dimensions around 100 nanometers are required for subwavelength, near-field optical microscopy. Another possible application is patterning on the micrometer and nanometer scale. The diodes have been made in the form of a sandwich structure, with the conductive polymer poly(3,4-ethylene-dioxythiophene) polymerized in the pores of commercially available microfiltration membranes defining the hole-injecting contacts, poly[3-(4-octylphenyl)-2,2;-bithiophene] as the light-emitting layer, and a thin film of calcium-aluminum as the electron injector.
TL;DR: The formation of a porous film is calculated for clusters impinging with low kinetic energy, while for the clusters with the highest energy a dense mirrorlike film is obtained, in good agreement with experiment.
Abstract: Langevin-molecular-dynamics simulations of thin-film growth by energetic cluster impact were carried out. The impact of a ${\mathrm{Mo}}_{1043}$ cluster on a Mo(001) surface was studied for impact energies of 0.1, 1, and 10 eV/atom using the Finnis-Sinclair many-body potential. The characteristics of the collision range from a soft touchdown at 0.1 eV/atom, over a flattening collision at 1 eV/atom, to a meteoric impact at 10 eV/atom. The highest energy impact creates a pressure of about 100 GPa in the impact zone and sends a strong shock wave into the material. The cluster temperature reaches a maximum of 596 K for 0.1 eV/atom, 1799 K for 1 eV/atom, and 6607 K for 10 eV/atom during the first ps after the touchdown. For energies of 1 and 10 eV/atom the cluster recrystallizes after 20 ps. The consecutive collision of 50 ${\mathrm{Mo}}_{1043}$ clusters with a Mo(001) surface at T=300 K was simulated for the three impact energies. The formation of a porous film is calculated for clusters impinging with low kinetic energy, while for the clusters with the highest energy a dense mirrorlike film is obtained, in good agreement with experiment.
TL;DR: In this paper, organometallic vapor phase epitaxy (OMVPE) was used to grow monocrystalline GaN(0001) thin films, void of oriented domain structures and associated low-angle grain boundaries.
Abstract: Monocrystalline GaN(0001) thin films, void of oriented domain structures and associated low‐angle grain boundaries, have been grown via organometallic vapor phase epitaxy (OMVPE) on high‐temperature monocrystalline AlN(0001) buffer layers predeposited on vicinal α(6H)–SiC(0001) wafers using TEG, TEA, and ammonia in a cold wall, vertical, pancake‐style reactor. The surface morphology was smooth, and the PL spectrum showed strong near‐band‐edge emission with a full width at half‐maximum (FWHM) value of 4 meV. The dislocation density within the first 0.5 μm was ≊1×109 cm−2; it decreased substantially with increasing film thickness. Controlled n‐type Si doping of GaN has been achieved for net carrier concentrations ranging from ∼1×1017 to 1×1020 cm−3. Double‐crystal XRC measurements indicated a FWHM value of 66 arcsec for the GaN(0004) reflection.
TL;DR: In this article, the optical properties of amorphous silicon nitride thin films have been extensively characterized by absorption, photoluminescence (PL), photolumininescence excitation, and electroluminecence measurements, and a simple qualitative model based on nitrogen and silicon dangling bonds adequately explains the observed PL features.
Abstract: Silicon nitride films were deposited at low temperatures (245–370 °C) and high deposition rates (500–1700 A/min) by hot filament assisted chemical vapor deposition (HFCVD). Optical properties of these amorphous silicon nitride thin films have been extensively characterized by absorption, photoluminescence (PL), photoluminescence excitation, and electroluminescence measurements. The optical band gap of the films was varied between 2.43 and 4.74 eV by adjusting the flow rate of the disilane source gas. Three broad peaks at 1.8, 2.4, and 3.0 eV were observed in the PL spectra from these films. A simple qualitative model based on nitrogen and silicon dangling bonds adequately explains the observed PL features. The photoluminescence intensity observed in these films was 8–10 times stronger than films deposited by plasma enhanced chemical vapor deposition, under similar conditions. The high deposition rates obtained by HFCVD is believed to introduce a large number of these optically active defects.
TL;DR: The distribution of crystallographic orientations of the grains in a polycrystalline film can evolve through a number of kinetic processes as mentioned in this paper, and the final texture of a film depends on which texture selection mechanisms and driving forces dominate, and is different for different films, substrates, and deposition conditions.
Abstract: The distribution of crystallographic orientations of the grains in a polycrystalline film can evolve through a number of kinetic processes. Orientation evolution can occur before, during and after coalescence of islands to form a continuous film, during thickening of a film, and during post-deposition annealing. The energetic constraints leading to texture selection include surface and interface energy minimization, as well as strain-energy minimization. The final texture of a film depends on which texture-selection mechanisms and driving forces dominate, and is different for different films, substrates, and deposition conditions.