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Showing papers in "Journal of Applied Physics in 1992"


Journal ArticleDOI
TL;DR: In this paper, x-ray photoelectron spectroscopy was used to investigate the oxidation mechanisms at 350°C during this initiation time period, and the oxide thickness increases slowly with oxidation time and the film appears to change from an amorphous TiO2 layer to a crystalline TiO 2 layer.
Abstract: We report a study of the oxidation of TiN. In previous work, the oxidation kinetics for 350–450 °C were reported and an initiation time prior to fast oxidation was identified. In this study, x‐ray photoelectron spectroscopy was used to investigate the oxidation mechanisms at 350 °C during this initiation time period. The oxide thickness increases slowly with oxidation time and the film appears to change from an amorphous TiO2 layer to a crystalline TiO2 layer. Spectral features which are intermediate between TiO2 and TiN are reported and a model involving grain boundary oxidation is proposed. One of the thicker oxides studied was annealed in vacuum to 700 °C. Following oxidation, some of the capping oxide and much of the intermediate material is no longer in the analysis volume and we suggest that the oxygen and nitrogen is being dissolved into the bulk in much the same way that nonevaporable getters are activated before use.

1,078 citations


Journal ArticleDOI
TL;DR: In this article, various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon.
Abstract: Recent reports describing photoluminescence in porous silicon have heightened the level of interest in it as a unique electronic material, and have created a need for a more complete understanding of the mechanism of porous silicon formation. The various models describing porous silicon formation are reviewed and the known electrochemical and morphological properties are discussed with the intention of unifying the different models into a comprehensive explanation for the formation of a porous structure in silicon. Because the specific surface dissolution chemistry is critical for a complete understanding of pore formation, some of the more prominent dissolution reactions are also reviewed and their relative importance to pore generation and morphology is discussed. Some aspects of the recently reported quantum effects are also reviewed. Because the mechanism of porous silicon formation involves a wide range of interdisciplinary fields, a considerable number of analogies and examples to related phenomena ...

1,000 citations


Journal ArticleDOI
TL;DR: In this paper, the authors combined thermal wave and thermography to provide a short-time low-frequency phase angle image where non-thermal features can be suppressed using lock-in data analysis.
Abstract: Thermography and thermal wave techniques can be combined to provide in a short‐time low‐frequency phase angle images where nonthermal features can be suppressed. The principle is optical thermal wave generation simultaneously on the whole sample surface and sequential monitoring of all pixels using both thermographic techniques and lock‐in data analysis. Due to parallel stationary excitation one can use low modulation frequencies allowing for a depth range that is of relevance for applications.

638 citations


Journal ArticleDOI
TL;DR: In this article, a general formalism for multicomponent diffusion in simple phases is presented in some detail, which is mainly based on previous work by various authors, and the purpose of the present work is to develop the formalism to such an extent that it is suitable for implementation on a computer.
Abstract: A general formalism for multicomponent diffusion in simple phases is presented in some detail. The formalism is mainly based on previous work by various authors. The purpose of the present work is to develop the formalism to such an extent that it is suitable for implementation on a computer. Expressions for the multicomponent diffusion‐coefficient matrix is given. The concentration dependence of the kinetic coefficients is discussed in terms of simple models.

635 citations


Journal ArticleDOI
TL;DR: In this article, aluminum-doped zinc oxide films have been deposited on soda lime glass substrates from diethyl zinc, triethyl aluminum, and ethanol by atmospheric pressure chemical-vapor deposition in the temperature range 367-444°C.
Abstract: Aluminum‐doped zinc oxide films have been deposited on soda lime glass substrates from diethyl zinc, triethyl aluminum, and ethanol by atmospheric pressure chemical‐vapor deposition in the temperature range 367–444 °C. Film roughness was controlled by the deposition temperature and the dopant concentration. The films have resistivities as low as 3.0 × 10−4 Ω cm, infrared reflectances close to 90%, visible transmissions of 85%, and visible absorptions of 5.0% for a sheet resistance of 4.0 Ω/⧠. The aluminum concentration within doped films measured by electron microprobe is between 0.3 and 1.2 at. %. The electron concentration determined from Hall coefficient measurements is between 2.0 × 1020 and 8.0 × 1020 cm−3, which is in agreement with the estimates from the plasma wavelength. The Hall mobility, obtained from the measured Hall coefficient and dc resistivity, is between 10.0 and 35.0 cm2/V s. Over 90% of the aluminum atoms in the film are electrically active as electron donors. Scanning electron microscopy and x‐ray diffraction show that the films are crystalline with disklike structures of diameter 100–1000 nm and height 30–60 nm. The films have the desired electrical and optical properties for applications in solar cell technology and energy efficient windows.

592 citations


Journal ArticleDOI
TL;DR: In this article, the operation of the ferroelectric nonvolatile memory field effect transistor is theoretically examined extensively for the first time, and the theoretical results provide unique insight into the effects of geometrical and material parameters on the electrical properties of the transistor.
Abstract: The operation of the ferroelectric nonvolatile memory field effect transistor is theoretically examined extensively for the first time. The ferroelectric transistor device properties are derived by combining the silicon charge‐sheet model of metal‐oxide‐semiconductor field‐effect transistor device operation with Maxwell’s first equation which describes the properties of the ferroelectric film. The model we present describes ferroelectric transistor I‐V and C‐V behavior when time‐dependent voltages are applied which result in hysteresis due to ferroelectric switching. The theoretical results provide unique insight into the effects of geometrical and material parameters on the electrical properties of the transistor. These parameters include the ferroelectric spontaneous and remanent polarization, the coercive field, and dielectric layer thicknesses. We have found that the conventional concept of threshold voltage is no longer useful, and that increasing the spontaneous polarization has only a minor impact ...

438 citations


Journal ArticleDOI
TL;DR: In this article, the experimentally observed dependence of effective surface recombination velocity Seff at the Si-SiO2 interface on light-induced minority carrier excess concentration is compared with theoretical predictions of an extended Shockley-Read-Hall (SRH) formalism.
Abstract: The experimentally observed dependence of effective surface recombination velocity Seff at the Si‐SiO2 interface on light‐induced minority carrier excess concentration is compared with theoretical predictions of an ‘‘extended Shockley–Read–Hall (SRH) formalism.’’ The calculations of SRH‐recombination rates at the Si‐SiO2 interface are based on the theory of a surface space charge layer under nonequilibrium conditions and take into account the impact of illumination level, gate metal work function, fixed oxide charge density, and the energy dependence of capture cross sections σn, σp and interface state density Dit. Applying this theory to p‐type silicon surfaces covered by high quality thermal oxides, the experimentally observed strong increase of Seff with decreasing minority carrier excess concentration could quantitatively be attributed to the combined effect of the σn/σp ratio of about 1000 at midgap and the presence of a positive fixed oxide charge density Qf of about 1×1011 charges/cm2. Due to the f...

429 citations


Journal ArticleDOI
TL;DR: The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper.
Abstract: The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper. Intermixing in these films was followed as a function of annealing temperature by in situ resistance measurements, Rutherford backscattering spectra, scanning electron microscopy, and cross‐section transmission electron microscopy. Ta prevents Cu‐silicon interaction up to 550 °C for 30 min in flowing purified He. At higher temperatures, copper penetration results in the formation of η‘‐Cu3Si precipitates at the Ta‐Si interface. Local defect sites appear on the surface of the sample in the early stages of this reaction. The Ta subsequently reacts with the substrate at 650 °C to form a planar hexagonal‐TaSi2 layer. Ta silicide formation, which does not occur until 700 °C in a Ta‐Si binary reaction couple, is accelerated by the presence of Cu. Nitrogen‐alloyed Ta is a very similar...

422 citations


Journal ArticleDOI
TL;DR: In this paper, the amplitude and phase of the electromagnetic radiation from the semiconductor surfaces depend on carrier mobility, impurity doping concentration, and strength and polarity of the static internal field.
Abstract: The basic concepts and preliminary applications of optically induced electromagnetic radiation from semiconductor surfaces and interfaces by using femtosecond optics are discussed. This submillimeter‐wave radiation provides a novel optoelectronic technique to study semiconductor electronic surface and interface properties with a contactless approach. The amplitude and phase of the electromagnetic radiation from the semiconductor surfaces depend on carrier mobility, impurity doping concentration, and strength and polarity of the static internal field. A large selection of bulk, epitaxial layer and superlattice samples from III‐V, II‐VI and group‐IV semiconductors has been tested. The orientation and strength of the static built‐in fields of a wide range of semiconductor surfaces, such as surface depletion, metal/semiconductor Schottky, p‐n junction and strain‐induced piezoelectric fields, can be determined and estimated.

412 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laserirradiation.
Abstract: Flash laser heating using short‐pulsed laser irradiation of a surface is demonstrated to be a promising new approach for effective removal of particulate contaminations of sizes as small as 0.1 μm. This is very useful because micron‐ and submicron‐sized particulates adhere tenaciously onto a solid surface, and conventional cleaning techniques are inadequate for removal. Several varieties of the new laser‐cleaning techniques have been developed by us as well as by others. For example, the pulsed laser irradiation can be used with or without the simultaneous deposition of a thin liquid film on the surface to be laser cleaned. The laser wavelength can also be chosen so that absorption occurs mainly at the sample surface, or in the liquid, or in the particulate, or in a combination of these. In this paper, we discuss and compare examples of these different approaches. We find that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laserirradiation. This permits the effective removal of particles smaller than ∼20 μm, down to as small as 0.1 μm, from a solid surface using a modest ultraviolet laser fluence of ∼0.1 J/cm2.

393 citations


Journal ArticleDOI
TL;DR: In this paper, a steady state model for resistivity of composites is presented, based on the idea that the resistance through a composite is the result of a series of a large number of resistors combined in series and parallel.
Abstract: A steady‐state model for the resistivity of composites is presented, based on the idea that the resistance through a composite is the result of a series of a large number of resistors combined in series and parallel. There are three separate contributions to the resistance: constriction resistance at the contacts, tunneling resistance at the contacts, and the intrinsic filler resistance through each particle, with tunneling resistance generally dominating the magnitude of the overall resistance. The model predicts resistivity increases with increasing filler hardness and/or elastic modulus and insulating film thickness, while resistivity decreases with increasing particle size and intrinsic stress. The room‐temperature dc resistivity behavior of conductor‐filled silicone rubber composites was investigated to verify the model. Comparison of the model to this experimental data showed that good agreement could be obtained for filler materials in which the tarnish layer was a known quantity for a given powder...

Journal ArticleDOI
TL;DR: In this article, the Coulomb blockade was used to block all tunnel events near zero bias voltage in series arrays of ultrasmall junctions, an effect that has come to be known as the ‘Coulomb blockade.
Abstract: A finite charging energy, e2/2C’, is required in order to place a single electron onto a small isolated electrode lying between two tunnel junctions and having a total capacitance C’ to its external environment. Under suitable conditions, this elemental charging energy can effectively block all tunnel events near zero bias voltage in series arrays of ultrasmall junctions, an effect that has come to be known as the ‘‘Coulomb blockade.’’ This article outlines a new approach to the design of digital logic circuits utilizing the Coulomb blockade in capacitively biased double‐junction series arrays. A simple ‘‘on’’/‘‘off ’’ switch is described and complementary versions of this switch are then employed to design individual logic gates in precise correspondence with standard complementary metal–oxide semiconductor architecture. A planar nanofabrication technique is also described that may eventually allow the integration of Coulomb blockade logic onto conventional semiconductor chips, thereby realizing hybrid i...

Journal ArticleDOI
TL;DR: In this article, GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave-plasma assisted molecular beam epitaxy, using a two-step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is growing at higher temperatures.
Abstract: GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave‐plasma‐assisted molecular‐beam epitaxy, using a two‐step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is grown at higher temperatures. This method of film growth was shown to lead to good single‐crystalline β‐GaN and to promote lateral growth resulting in smooth surface morphology. The full width at half‐maximum of the x‐ray rocking curve in the best case was found to be 60 min. Optical‐absorption measurements indicate that the band gap of β‐GaN is 3.2 eV and the index of the refraction below the absorption edge is 2.5. Conductivity measurements indicate that the films may have a carrier concentration below 1017 cm−3.

Journal ArticleDOI
TL;DR: In this article, the structural properties of these IO films were investigated using x-ray diffraction, scanning electron microscope, and electron spectroscopy for chemical analysis, in comparison with the films formed by conventional magnetron sputtering and EB evaporation.
Abstract: Tin‐doped indium oxide (ITO) films with the resistivity less than 1.35×10−4 Ω cm were formed by low voltage dc magnetron sputtering (LVMS) and highly dense plasma‐assisted electron beam (EB) evaporation using the arc plasma generator (HDPE). The structural properties of these films were investigated using x‐ray diffraction, scanning electron microscope, and electron spectroscopy for chemical analysis, in comparison with the films formed by conventional magnetron sputtering and EB evaporation, in order to clarify the key factors for low resistivity. With decreasing plasma impedance and sputtering voltages from 540 to 380 V, the resistivity of the films deposited at Ts=400 °C decreased from 1.92 to 1.34×10−4 Ω cm, due mostly to increase in the carrier density. This LVMS film showed higher crystallinity because of lower damages of high‐energy particles during the deposition, which might increase the number of electrically active species. For HDPE, the film with resistance of 1.23×10−4 Ω cm was deposited at T...

Journal ArticleDOI
TL;DR: In this article, a comparative study of the Schottky barrier height variation on sulfide-treated GaAs(100) surfaces with low work function metal contacts was made using currentvoltage and capacitance-voltage measurements.
Abstract: A comparative study of the Schottky barrier height variation on sulfide‐treated GaAs(100) surfaces with low work function metal contacts was made using current‐voltage and capacitance‐voltage measurements. Five different wet chemical sulfide treatments were found to cause little variation in the Sm (0.72 eV) and Mg (0.59 eV) Schottky barrier heights, but caused significant variation in the Al (0.58–0.75 eV) barrier heights when compared to the untreated control diodes. A low temperature (160 °C) anneal was found to cause variation in all of these, uniformly raising the barrier heights of the Sm (+0.07 eV) and Al (+0.04 eV) contacts, and degrading the Mg contacts. These results demonstrate the critical importance of both the reaction specifics and the stability of the interface on the Schottky barrier height.

Journal ArticleDOI
TL;DR: In this article, the effect of source/drain (S/D) parasitic resistance has been experimentally investigated for amorphous silicon thin film transistors (TFTs), and the results showed that the current spreading under the S/D regions is most critical in determining the magnitude of the total parasitic resistance.
Abstract: The effect of source/drain (S/D) parasitic resistance has been experimentally investigated for amorphous silicon (a‐Si:H) thin film transistors (TFTs). In general, the apparent field effect mobility decreases with decreasing channel length. However, the apparent threshold voltage is relatively constant. This may be attributed to an ohmic parasitic resistance due to the use of ion‐implanted n+ S/D regions. Self‐consistent results were obtained from both TFTs and from independent test structures for the TFT parasitic resistance, contact resistance, and sheet resistance. The results showed that the current spreading under the S/D regions is most critical in determining the magnitude of the total parasitic resistance. In this regard, both the S/D ion implantation and the S/D to gate overlap reduce the total parasitic resistance. Finally, the parasitic resistance is modeled as a gate voltage‐modulated channel resistance, under the gate overlap, in series with a constant minimum contact resistance.

Journal ArticleDOI
TL;DR: In this article, forces between particles aligned into chains by an applied electric field in an electrorheological (ER) fluid are calculated using finite element techniques and, approximately, using a dipole approximation with local field effects.
Abstract: Forces between particles aligned into chains by an applied electric field in an electrorheological (ER) fluid are calculated using finite‐element techniques and, approximately, using a dipole approximation with local‐field effects. Evaluation of the effective dielectric constant is emphasized and the shear modulus is derived from the shear dependence. For high‐frequency (f≳0.1–1 kHz) applied electric fields, the forces and the modulus depend upon the dielectric constants of the suspending fluid and the dispersed particles. For low‐frequency or dc electric fields, the conductivities of the components are dominant. These effects are treated within a Maxwell–Wagner approach. If the ratio of particle‐to‐fluid conductivities substantially exceeds the ratio of dielectric constants, a large enhancement of the modulus is found. Implications for the design of ER fluids are discussed briefly.

Journal ArticleDOI
TL;DR: In this paper, it was shown that for a given temperature, the controlling factor in the resulting thin film phase is the momentum transferred into the film per depositing boron atom.
Abstract: Ion beam assisted evaporation was used to deposit cubic and hexagonal boron nitride thin films. Boron was evaporated and bombardment was by argon and nitrogen ions. The effect of preparation conditions on the resulting phase was studied, and the relationship between the phase and the energy and momentum transferred into the film through ion bombardment was examined. It is shown that for a given temperature, the controlling factor in the resulting thin film phase is the momentum transferred into the film per depositing boron atom. At 300–400 °C a sharp threshold value of momentum‐per‐atom exists below which films are hexagonal and above which they are cubic. For 400 °C this threshold occurred at 200 (eV×amu)1/2 which is equal to 3.3×10−21 m kg s−1. Depositions performed using krypton and xenon instead of argon as the second bombarding gas confirmed this momentum‐per‐atom value. A second threshold was also observed, which was bombarding species dependent, above which either complete resputtering of the deposited material or reversion to the hexagonal phase occurred. Cubic boron nitride deposition was seen to occur in a window of momentum‐per‐atom values between these two thresholds. Using this information it was possible to grow cubic boron nitride using only nitrogen bombardment, although the window of momentum‐per‐atom values for nitrogen is very narrow. The effect of substrate temperature was studied, and it was found to be difficult to grow predominantly cubic phase films below 300–400 °C. The relationship between intrinsic stress and phase of the films is also discussed. A diagram is presented showing film phase as a function of bombardment, substrate temperature, and system chemistry. The parameter of momentum‐per‐atom is shown to combine into a single value the variables of ion beam assisted deposition: deposition rate, ion energy, ion flux, and ion species. It is suggested that, in general, for properties affected by ion bombardment the momentum‐per‐atom transferred into the film is the controlling factor. The results are shown to support momentum transfer as the dominant process in cubic boron nitride thin film formation.

Journal ArticleDOI
TL;DR: In this paper, a superconducting film of 70 nm thickness with zero-field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K was prepared by annealing at 780 and 830 °C in 2.5 × 10−4−1 × 10 −3 atm oxygen furnace atmospheres.
Abstract: Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single‐crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high‐temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low‐oxygen partial pressures. Superconducting films of 70 nm thickness with zero‐field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c‐axis normal BYC near the film/substrate interface with the overlying mater...

Journal ArticleDOI
TL;DR: In this paper, the effect of a variety of process parameters on the film properties is investigated, and the effects of a low pressure hydrogen background and the use of auxiliary pulsed and dc plasma enhancements are also examined.
Abstract: Carbon thin films have been prepared by 248 nm excimer laser vaporization of graphite targets. The effect of a variety of process parameters on the film properties is investigated. Deposition at or below room temperature yields diamond‐like films with low hydrogen content, high optical transmission, and high resistivity. Electron energy loss spectra indicate sp3 bond fractions of 70–85%. Detailed analyses of the pseudodielectric functions, measured using spectroscopic ellipsometry, show the films to have normal dispersion and an index of refraction of 2.5 in the visible wavelength region. The effects of a low pressure hydrogen background and the use of auxiliary pulsed and dc plasma enhancements are also examined.

Journal ArticleDOI
TL;DR: In this paper, the Maxwell displacement current generated from single fatty acid monolayers containing azobenzene by photoisomerization was investigated in the context of the phase diagram of monoline on a water surface.
Abstract: The Maxwell displacement current generated from single fatty acid monolayers containing azobenzene by photoisomerization was investigated in the context of the phase diagram of monolayers on a water surface. Transient displacement‐current pulses were found to be produced when successive isomerizations were induced in monolayers by irradiation with ultraviolet and visible light. In contrast, the displacement current was never generated in the so‐called solid phase by the application of surface pressure or photoirradiation, probably because of the lack of free volume for the isomerizing chromophore in single monolayers and as well as the aggregation of molecules in the monolayer. The displacement current generated during monolayer compression was also investigated in connection with phase transitions.

Journal ArticleDOI
TL;DR: The elastic constants of single-crystal NbN, VN, and TiN films were determined from surface acoustic wave (SAW) dispersion curves obtained by the use of an acoustic microscope with a line-focus beam as mentioned in this paper.
Abstract: The elastic constants of single‐crystal NbN, VN, and TiN films were determined from surface acoustic wave (SAW) dispersion curves obtained by the use of an acoustic microscope with a line‐focus beam. Measurements were carried out for single‐crystal nitride films grown on the (001) plane of single‐crystal cubic‐symmetric MgO substrates. The phase velocities measured as functions of the angle of propagation display the expected anisotropy. Dispersion curves of SAWs propagating along the symmetry axes were obtained by measuring the wave velocities for various film thicknesses and frequencies. Using a modified simplex method, an inversion of the SAW dispersion data yielded the elastic constants of cubic symmetry, namely c11, c12, and c44. The Rayleigh surface wave velocities calculated from the determined elastic constants and known mass densities agree well with a result measured by Brillouin scattering spectroscopy reported elsewhere.

Journal ArticleDOI
TL;DR: In this article, a dielectric function model yielding a Gaussian shape of the absorption lines and satisfying Kramers-Kronig relations was suggested for modeling of infrared spectra.
Abstract: For the modeling of infrared spectra it is a common approach to use a dielectric function that treats the vibrational modes as damped harmonic oscillators. This model was found to be rather crude for some applications to amorphous solids. A dielectric function model yielding a Gaussian shape of the absorption lines and satisfying Kramers–Kronig relations is suggested. The model function is constructed by a convolution of a Gaussian function with the dielectric function of the damped harmonic oscillator model. An analytical solution of this integral is given. It is demonstrated that this model describes the spectra of thermally grown ultrathin (1.3 nm) silicon oxide films, plasma‐deposited silicon films, plasma‐deposited silicon nitride films, and amorphous aluminum oxide films very well. The physical motivation of the dielectric function model suggested is the randomness of the vibrational frequencies in an amorphous structure.

Journal ArticleDOI
TL;DR: Oxygen was observed to influence the electrical and optical properties of GaN layers grown by metalorganic vapor phase epitaxy as discussed by the authors, and a model based on impurity band formation was proposed to explain these experimental results.
Abstract: Oxygen was observed to influence the electrical and optical properties of GaN layers grown by metalorganic vapor phase epitaxy. The carrier concentrations obtained from Van der Pauw–Hall measurements increased an order of magnitude when oxygen was incorporated into the grown layers. Additionally, the presence of oxygen in the GaN layers also changed the compensation behavior of Zn. Anomalous behavior of optical transitions in the oxygen‐doped GaN layers was observed by optical absorption spectroscopy and low‐temperature (4.2 K) photoluminescence measurements. These properties were studied as a function of growth parameters including growth temperature, amount of doping, etc. A model based on impurity band formation is proposed to explain these experimental results, and it is concluded that oxygen is a ‘‘shallow’’ deep donor in GaN.

Journal ArticleDOI
TL;DR: In this paper, the effect of substrate temperature and annealing on the packing density, refractive index, extinction coefficient, and crystallinity of the titania films has been investigated for their structural and optical characteristics.
Abstract: This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10−3 to 10.4× 10−3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10−3 to 11.6 × 10−3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. ...

Journal ArticleDOI
TL;DR: In this article, the luminescence properties of 3 μm thick, strongly emitting, and highly porous silicon films were studied using a combination of photoluminescence, transmission electron microscopy, and Fourier transform infrared spectroscopy.
Abstract: The luminescence properties of 3 μm thick, strongly emitting, and highly porous silicon films were studied using a combination of photoluminescence, transmission electron microscopy, and Fourier transform infrared spectroscopy. Transmission electron micrographs indicate that these samples have structures of predominantly 6–7 nm size clusters (instead of the postulated columns). In the as‐prepared films, there is a significant concentration of Si—H bonds which is gradually replaced by Si—O bonds during prolonged aging in air. Upon optical excitation these films exhibit strong visible emission peaking at ≊690 nm. The excitation edge is shown to be emission wavelength dependent, revealing the inhomogeneous nature of both the initially photoexcited and luminescing species. The photoluminescence decay profiles observed are highly nonexponential and decrease with increasing emission energy. The 1/e times observed typically range from 1 to 50 μs. The correlation of the spectral and structural information suggest...

Journal ArticleDOI
TL;DR: In this article, the gallium doped zinc oxide films have been deposited in the temperature range 150 to 470°C from 0.05% diethyl zinc, 0.8% water, and various triethyl gallium concentrations.
Abstract: Gallium doped zinc oxide films have been deposited in the temperature range 150 to 470 °C from 0.05% diethyl zinc, 0.8% water, and various triethyl gallium concentrations. The films are polycrystalline with crystallite sizes varying between 275 and 500 A for undoped films and between 125 and 400 A for doped films. Only those films deposited above 430 °C are highly oriented and have their c axes perpendicular to the substrate plane. The electron density, conductivity, and mobility always increase with temperature. Thicker films have higher conductivity and mobility than thinner films. The refractive index is reduced from 1.96 to 1.73 when the electron density is increased from zero to 3.7×1020 cm−3. For films deposited at 370 °C with a gallium concentration of about 2.5 at. %, the ratio of conductivity to visible absorption coefficient increases from 0.03 to 1.25 Ω−1 when the film thickness increases from 0.11 to 1.2 μm. A film deposited at 470 °C with a gallium concentration of 2.4 at. % and a thickness o...

Journal ArticleDOI
TL;DR: In this article, the authors show that when the growth conditions are very clean and the gradient is shallow enough (about 1% misfit per half micron), very good, relaxed films are obtained.
Abstract: Compositionally graded films of SiGe/Si(100) and GaInAs/GaAs were grown under different conditions in order to investigate the different modes of strain relaxation associated with the compositional grading. We show that, when the growth conditions are very clean and the gradient is shallow enough (about 1% misfit per half micron), very good, relaxed films are obtained. This coincides with the introduction of large numbers of dislocations in the substrate itself, which is counter‐intuitive at first since the substrate is under negligible strain. We show that this introduction of dislocations is the result of the activation of novel Frank–Read‐like sources located in the graded region, and is directly correlated to the lack of other low energy nucleation sites for dislocations. We detail the conditions of growth necessary for this phenomenon to occur, and show that it operates both for the SiGe/Si system and the GaInAs/GaAs system. Pure, relaxed Ge films have been grown in this manner on Si(100), with a defect density as low as 106/cm2.

Journal ArticleDOI
TL;DR: The photovoltaic characteristics of the three-layer configuration suggest the formation of a p-i-n like structure, in which the built-in potential produced by Fermi level differences in the respective pigment layers is mainly distributed across the co-deposited interlayer.
Abstract: Three‐layered organic solar cells, having a sandwiched interlayer of co‐deposited p‐type phthalocyanine (Pc) pigments and n‐type perylene derivative (PTC) pigments, exhibited photocurrent enhancement when compared with two‐layered cells without the interlayer. A large number of Pc/PTC molecular contacts within the interlayer serve as active sites for effective charge carrier photogeneration. The photovoltaic characteristics of the three‐layered configuration suggest the formation of a p‐i‐n like structure, in which the built‐in potential produced by Fermi level differences in the respective pigment layers is mainly distributed across the co‐deposited interlayer. Inorganic semiconductor films are also shown to be applicable to the present p‐i‐n cell structure as an n layer to obtain larger photovoltages.

Journal ArticleDOI
TL;DR: In this paper, the vibrational spectra of the chalcopyrite compounds CuInSe2 and CuGaSe2 have been studied by Raman microspectrometry.
Abstract: The vibrational spectra of the chalcopyrite compounds CuInSe2 and CuGaSe2 have been studied by Raman microspectrometry. This technique is very useful in the present case where large single crystals are not generally available. The results have been used to resolve discrepancies in the reported data on the vibrational spectrum of CuInSe2.