Showing papers on "Nitride published in 2002"

Pyroelectric properties of Al(In)GaN/GaN hetero- and quantum well structures

Abstract: The macroscopic nonlinear pyroelectric polarization of wurtzite AlxGa1-xN, InxGa1-xN and AlxIn1-xN ternary compounds (large spontaneous polarization and piezoelectric coupling) dramatically affects the optical and electrical properties of multilayered Al(In)GaN/GaN hetero-, nanostructures and devices, due to the huge built-in electrostatic fields and bound interface charges caused by gradients in polarization at surfaces and heterointerfaces. Models of polarization-induced effects in GaN-based devices so far have assumed that polarization in ternary nitride alloys can be calculated by a linear interpolation between the limiting values of the binary compounds. We present theoretical and experimental evidence that the macroscopic polarization in nitride alloys is a nonlinear function of strain and composition. We have applied these results to interpret experimental data obtained in a number of InGaN/GaN quantum wells?(QWs) as well as AlInN/GaN and AlGaN/GaN transistor structures. We find that the discrepancies between experiment and ab initio theory present so far are almost completely eliminated for the AlGaN/GaN-based heterostructures when the nonlinearity of polarization is accounted for. The realization of undoped lattice-matched AlInN/GaN heterostructures further allows us to prove the existence of a gradient in spontaneous polarization by the experimental observation of two-dimensional electron gases?(2DEGs). The confinement of 2DEGs in InGaN/GaN QWs in combination with the measured Stark shift of excitonic recombination is used to determine the polarization-induced electric fields in nanostructures. To facilitate inclusion of the predicted nonlinear polarization in future simulations, we give an explicit prescription to calculate polarization-induced electric fields and bound interface charges for arbitrary composition in each of the ternary III-N alloys. In addition, the theoretical and experimental results presented here allow a detailed comparison of the predicted electric fields and bound interface charges with the measured Stark shift and the sheet carrier concentration of polarization-induced 2DEGs. This comparison provides an insight into the reliability of the calculated nonlinear piezoelectric and spontaneous polarization of group III nitride ternary alloys.

Substrates for gallium nitride epitaxy

Abstract: In this review, the structural, mechanical, thermal, and chemical properties of substrates used for gallium nitride (GaN) epitaxy are compiled, and the properties of GaN films deposited on these substrates are reviewed. Among semiconductors, GaN is unique; most of its applications uses thin GaN films deposited on foreign substrates (materials other than GaN); that is, heteroepitaxial thin films. As a consequence of heteroepitaxy, the quality of the GaN films is very dependent on the properties of the substrate—both the inherent properties such as lattice constants and thermal expansion coefficients, and process induced properties such as surface roughness, step height and terrace width, and wetting behavior. The consequences of heteroepitaxy are discussed, including the crystallographic orientation and polarity, surface morphology, and inherent and thermally induced stress in the GaN films. Defects such as threading dislocations, inversion domains, and the unintentional incorporation of impurities into the epitaxial GaN layer resulting from heteroepitaxy are presented along with their effect on device processing and performance. A summary of the structure and lattice constants for many semiconductors, metals, metal nitrides, and oxides used or considered for GaN epitaxy is presented. The properties, synthesis, advantages and disadvantages of the six most commonly employed substrates (sapphire, 6H-SiC, Si, GaAs, LiGaO 2 , and AlN) are presented. Useful substrate properties such as lattice constants, defect densities, elastic moduli, thermal expansion coefficients, thermal conductivities, etching characteristics, and reactivities under deposition conditions are presented. Efforts to reduce the defect densities and to optimize the electrical and optical properties of the GaN epitaxial film by substrate etching, nitridation, and slight misorientation from the (0 0 0 1) crystal plane are reviewed. The requirements, the obstacles, and the results to date to produce zincblende GaN on 3C-SiC/Si(0 0 1) and GaAs are discussed. Tables summarizing measures of the GaN quality such as XRD rocking curve FWHM, photoluminescence peak position and FWHM, and electron mobilities for GaN epitaxial layers produced by MOCVD, MBE, and HVPE for each substrate are given. The initial results using GaN substrates, prepared as bulk crystals and as free-standing epitaxial films, are reviewed. Finally, the promise and the directions of research on new potential substrates, such as compliant and porous substrates are described.

Evidence for nonlinear macroscopic polarization in III-V nitride alloy heterostructures

Abstract: We provide explicit rules to calculate the nonlinear polarization for nitride alloys of arbitrary composition, and hence, the bound sheet charge induced by polarization discontinuity at the interfaces between different alloy and binary (epi)layers. We then present experimental results and simulations of polarization-related quantities in selected nitride-alloy-based heterostructure systems. The agreement of experiment and simulation, also in comparison to previous approaches, strongly suggests that the macroscopic polarization of nitride alloys is indeed nonlinear as a function of composition.

Properties of GaN and related compounds studied by means of Raman scattering

Abstract: In the last decade, we have seen very rapid and significant developments in Raman scattering experiments on GaN and related nitride compounds: the Γ-point phonon frequencies have been identified for both cubic and hexagonal structures of binary compounds of GaN, AlN, and InN. The phonon spectra of their ternary alloys, InGaN and AlGaN, were also intensively studied. On the basis of these studies, characterizations of strain, compositional fluctuation, defects, impurities, etc, are now being intensively conducted. Besides such pure lattice properties, coupled modes between a lattice vibration (LO phonon) and a collective excitation of free carriers (plasmon) in GaN have been thoroughly studied, and the results are now widely applied to characterize carrier-transport properties. Low-dimensional structures of nitrides such as quantum dots and superlattices will soon enter the most active field of Raman scattering characterization. This article briefly reviews the present status of Raman scattering experiments on GaN and related nitride compounds and presents some future prospects.

Rationalization of the Low-Potential Reactivity of 3d-Metal-Based Inorganic Compounds toward Li

Abstract: The unusual low-potential Li reactivity toward simple 3d-metal oxides can be accounted for by classical thermodynamie predictions and simpe acid-basic considerations. The Smith's scale, defined in solids for acido-basic reactions involving O 2 species exchange, is successfully used to check that, among the numerous simple oxides, the basic ones such as MnO, FeO, CoO, NiO, and CuO should reversibly react with lithium. Besides the basicity criteria, we stressed that the nanometric character of the reduced composite electrode (e.g., metallic nanoparticles immersed in a highly divided Li 2 O media) is a must to enable the reversible reactivity of metal oxides toward Li. Such a simple approach was nally implemented to other compounds (sulfides, nitrides, vanadates....) and the predictions confronted with experimental data.

Organic electroluminescent element

Abstract: PROBLEM TO BE SOLVED: To provide an organic electroluminescent element which is driven at a low voltage, and exhibits high efficiency and durability. SOLUTION: The organic electroluminescent element 1 includes an anode (a transparent electrode 14), a cathode (a metal electrode 10), and an organic compound layer containing a light emitting layer 12 and interposed between the anode and cathode. The light emitting layer 12 contains an indolo azacarbazole compound expressed by a general formula (1). In the formula (1), either Q 1 or Q 2 is a nitride atom, and one which is not the nitride atom out of Q 1 and Q 2 is CH. Ar 1 and Ar 2 express a substituted or non-substituted aryl group, respectively, and may be the same or different. R 1 to R 8 express a hydrogen atom, a substituted or a non-substituted alkyl group, or a substituted or a non-substituted aryl group, and may be the same or different. COPYRIGHT: (C)2011,JPO&INPIT

Group III nitride based light emitting diode structures with a quantum well and superlattice, group III nitride based quantum well structures and group III nitride based superlattice structures

Abstract: A Group III nitride based semiconductor device is disclosed, comprising: a doped Group III nitride layer; and a gallium nitride based superlattice directly on the doped Group III nitride layer, the gallium nitride superlattice being doped with an n-type impurity and having at least two periods of alternating layers of InXGa1-XN and InYGa1-YN, where 0 ≤ X < 1 and X is not equal to Y and wherein a thickness of a first of the alternating layers is less than a thickness of a second of the alternating layers.

Characterization of nitride coatings by XPS

Abstract: Nitride coatings have been used in numerous applications to increase the hardness and improve the wear and corrosion resistance of structural materials, as well as in various high-tech areas, where their functional rather than mechanical properties are of prime importance. Performance of these coatings is equally dependent on their chemical composition and long-range crystalline structure, as well as on the nature and amount of impurities and intergranular interactions. Significant improvement in the mechanical properties has recently been achieved with multi-component superlattice and nanocomposite nitride coatings. In the case of such multi-component systems, not only is close control of the elemental composition (stoichiometry) necessary to optimize the properties of the coatings, but the influence of chemical bond formation between the components is also of prime importance. Special care needs to be taken when non-equilibrium preparation conditions, activation of CVD and PVD by plasmas or energetic particle beams are applied, occasionally leading to unpredicted deviations, both in composition and structure. As is highlighted in this paper, nitride coatings or nitrided surfaces can be analyzed in detail by X-ray photoelectron spectroscopy (XPS) due to its excellent element selectivity, quantitative character and high surface sensitivity. More importantly, XPS reflects the atomic scale chemical interactions, i.e. the bonds between neighboring atoms, and thus it also provides reliable structural characteristics for amorphous or nano-crystalline coatings of complex composition, for which application of diffraction techniques is not straightforward. A number of examples of the application of XPS are given for various types of nitride coatings, including interstitial compounds, such as TiN, CrNx, etc., as well as compounds with predominantly covalent bonding, such as AlN, GaN, Si3N4 and CNx. Special emphasis is placed on ion beam-induced compositional and structural changes and to the formation of ‘superstoichiometric’ TiN1+x, ZrN1+x compounds.

Gallium nitride materials and methods

Abstract: The invention provides semiconductor materials including a gallium nitride material layer formed on a silicon substrate and methods to form the semiconductor materials. The semiconductor materials include a transition layer formed between the silicon substrate and the gallium nitride material layer. The transition layer is compositionally-graded to lower stresses in the gallium nitride material layer which can result from differences in thermal expansion rates between the gallium nitride material and the substrate. The lowering of stresses in the gallium nitride material layer reduces the tendency of cracks to form. Thus, the invention enables the production of semiconductor materials including gallium nitride material layers having few or no cracks. The semiconductor materials may be used in a number of microelectronic and optical applications.

Thermal conductivity of polystyrene–aluminum nitride composite

Abstract: The thermal conductivity of polymer composites having a matrix of polystyrene (PS) containing aluminum nitride (AlN) reinforcement has been investigated under a special dispersion state of filler in the composites: aluminum nitride filler particles surrounding polystyrene matrix particles. Data for the thermal conductivity of the composites are discussed as a function of composition parameters (aluminum nitride concentration, polystyrene particle size) and temperature. It is found that the thermal conductivity of composites is higher for a polystyrene particle size of 2 mm than that for a particle size of 0.15 mm. The thermal conductivity of the composite is five times that of pure polystyrene at about 20% volume fraction of AlN for the composite containing 2 mm polystyrene particle size. The relationship between thermal conductivity of composites and AlN filler concentrations has been compared with the predictions of two theoretical models from the literature.

Method of forming a multilayer dielectric stack

Abstract: A multilayer dielectric stack is provided which has alternating layers of a high-k material and an interposing material. The presence of the interposing material and the thinness of the high-k material layers reduces or eliminate effects of crystallization within the high-k material, even at relatively high annealing temperatures. The high-k dielectric layers are a metal oxide of preferably zirconium or hafnium. The interposing layers are preferably amorphous aluminum oxide, aluminum nitride, or silicon nitride. Because the layers reduce the effects of crystalline structures within individual layers, the overall tunneling current is reduced. Also provided are atomic layer deposition, sputtering, and evaporation as methods of depositing desired materials for forming the above-mentioned multilayer dielectric stack.

Field emission from open ended aluminum nitride nanotubes

Abstract: This letter reports the field emission measurements from the nanotubes of aluminum nitride which were synthesized by gas phase condensation using the solid-vapor equilibria. A dc arc plasma reactor was used for producing the vapors of aluminum in a reactive nitrogen atmosphere. Nanoparticles and nanotubes of aluminum nitride were first characterized by transmission electron microscope and tube dimensions were found to be varying from 30 to 200 nm in diameter and 500 to 700 nm in length. These tubes were mixed with nanoparticles of size range between 5 and 200 nm in diameter. Tungsten tips coated with these nanoparticles and tubes were used as a field emitter. The field emission patterns display very interesting features consisting of sharp rings which were often found to change their shapes. The patterns are attributed to the open ended nanotubes of aluminum nitride. A few dot patterns corresponding to the nanoparticles were also seen to occur. The Fowler–Nordheim plots were seen to be nonlinear in nature...

Electrical and spectroscopic comparison of HfO2/Si interfaces on nitrided and un-nitrided Si(100)

Abstract: The interfacial chemistry of the high-k dielectric HfO2 has been investigated on nitrided and un-nitrided Si(100) using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The samples are prepared by sputter depositing Hf metal and subsequently oxidizing it. A 600 °C densification anneal is critical to completing Hf oxidation. These spectroscopic data complement electrical testing of metal oxide semiconductor capacitors fabricated with ∼50 A HfO2 on nitrided and un-nitrided Si(100). Capacitors with interfacial nitride show reduced leakage current by a factor of 100 at a −1 V bias. Concurrently, interfacial nitride increased capacitance 12% at saturation. XPS shows that an interfacial layer composed of nonstoichiometric hafnium silicate (HfSixOy), forms at both the HfO2/Si and HfO2/SiNx interfaces. Differences in the Si 2p and O 1s XP spectra suggest more silicate forms at the un-nitrided interface. HfO2 films on un-nitrided Si show more O 1s and Si 2p photoemission intensity...

Semiconductor device and method of manufacturing the same

Abstract: A semiconductor device manufacturing method comprising the steps of: (a) forming an insulating film on a semiconductor substrate on which an element is formed; (b) selectively removing a predetermined region of the insulating film to form an opening portion so as to expose an underlying conductive layer; (c) depositing a refractory metal on the opening portion; (d) depositing refractory metal silicide on the refractory metal deposited on the opening portion; and (e) filling the opening portion by depositing a refractory nitride metal on the refractory metal silicide deposited on the opening portion.

Boron suboxide: As hard as cubic boron nitride

Abstract: The Vickers hardness of boron suboxide single crystals was measured using a diamond indentation method. Under a loading force of 0.98 N, our test gave an average Vickers hardness of 45 GPa. The average fracture toughness was measured as 4.5 MPa m1/2. We also measured the hardness of the cubic boron nitride and sapphire single crystals for comparison. The average measured hardness for boron suboxide was found to be very close to that of cubic boron nitride under the same loading force. Our results suggest that the boron suboxide could be a new superhard material for industrial applications, surpassed in hardness only by diamond and cubic boron nitride.

Synthesis of Porous Silicon Nitride with Unidirectionally Aligned Channels Using Freeze-Drying Process

Abstract: Porous silicon nitride with macroscopically aligned channels was synthesized using a freeze-drying process. Freezing of a water-based slurry of silicon nitride was done while unidirectionally controlling the growth direction of the ice. Pores were generated subsequently by sublimation of the columnar ice during freeze-drying. By sintering this green body, a porous silicon nitride with high porosity (over 50%) was obtained and its porosity was controllable by the slurry concentration. The porous Si 3 N 4 had a unique microstructure, where macroscopically aligned open pores contained fibrous grains protruding from the internal walls of the Si 3 N 4 matrix. It is hypothesized that vapor/solid phase reactions were important to the formation mechanism of the fibrous grains.

Theoretical investigation of native defects, impurities, and complexes in aluminum nitride

Abstract: We have performed density-functional pseudopotential calculations to investigate the electronic structure, atomic configurations, and formation energies of native point defects and impurities in AlN. For the native defects, the nitrogen vacancy has the lowest formation energy in p-type material and the aluminum vacancy has the lowest formation energy in n-type material. Under n-type conditions the formation energy of the nitrogen vacancy is high, indicating that it will not occur in high concentrations. We find that the nitrogen vacancy exhibits a different behavior in the zinc-blende and wurtzite structures with respect to the higher-lying defect-induced level: in zinc-blende materials, this level is a resonance in the conduction band causing the vacancy to act as a shallow donor, while in wurtzite the level lies well below the conduction-band edge causing the vacancy to act as a deep donor. In the zinc-blende structure we find, in addition, that the aluminum interstitial has a low formation energy in p-type material. The results indicate that these defects could be important compensation centers; we discuss this in relation to the dopant impurities O, Si, and Mg. We also investigate MgO and ${\mathrm{Mg}}_{2}{\mathrm{O}}_{2}$ impurity complexes. A comparison between results obtained using the local-density approximation and the generalized-gradient approximation for the exchange-correlation functional shows that the results are qualitatively very similar.

Silicon Nitride Ceramics

Abstract: Silicon nitride ceramics is a generic term for a variety of alloys of Si3N4 with additional compounds necessary for a complete densification of the Si3N4 starting powder. They are heterogeneous, multicomponent materials characterised by the inherent properties of the crystalline modifications α and β of Si3N4 and the significant influence of the densification additives. With a view to ability of the α and β modification to form solid solutions α-Si3N4 (αss) and β-Si3N4 (βss) solid solutions can be distinguished. Each group contains engineered materials with interesting properties for special applications. Phase relations and micro-structures determine the properties decisively. Composition of the phases, the distribution of the grains, their aspect ratio and the grain boundary phase are pronounced microstructural features. The formation of the microstructure strongly depends on the one hand on the quality of the Si3N4 starting powders, which closely is related to the chemistry of the production process, and on the other on the liquid phase sintering as the most important step in the densification route. The interrelation between pure Si3N4, the densification of the powder including the role of sintering additives, microstructural engineering, physicochemical properties of the sintered Si3N4 ceramics (SSN, GPSN, HPSN, HIP-SSN, HIP-SN) are described in more detail and compared to reaction bonded Si3N4 ceramics (RBSN), which are produced by nitridation of silicon powders.

Boron Nitrides — Properties, Synthesis and Applications

Abstract: Boron nitride is a extraordinary topic in the area of materials science. Due to the special bonding behaviors of boron and nitrogen the BN exists in many different structures. The well-defined crystallographic structures are hexagonal BN (h-BN), rhombohedral BN (r-BN), wurtzitic BN (w-BN), and cubic BN (c-BN). Additionally, other crystalline and amorphous structures exist. Exceptional is that there are still discussions about the BN phase diagram. In the present stage c-BN is the stable phase at standard conditions but exact data about the phase transition line are not yet available. Synthesis of h-BN powders and coatings is described as well as applications of BN in ceramic materials and as lubricant. For c-BN the high-pressure high-temperature synthesis for powder production is discussed, and an overview about applications in wear resistant ceramics (polycrystalline c-BN) is given. The low-pressure methods for nano-cBN deposition (PVD and Plasma CVD) are described.

Metal nitride formation

Abstract: A process for treating refractory metal-boron layers deposited by atomic layer deposition resulting in the formation of a ternary amorphous refractory metal-nitrogen-boron film is disclosed. The resulting ternary film remains amorphous following thermal annealing at temperatures up to 800° C. The ternary films are formed following thermal annealing in a reactive nitrogen-containing gas. Subsequent processing does not disrupt the amorphous character of the ternary film. arrangement where a blended solution is supplied to a remote point of use.

Strain balanced nitride heterojunction transistors and methods of fabricating strain balanced nitride heterojunction transistors

Abstract: A nitride based heterojunction transistor includes a substrate and a first Group III nitride layer, such as an AlGaN based layer, on the substrate. The first Group III-nitride based layer has an associated first strain. A second Group III-nitride based layer, such as a GaN based layer, is on the first Group III-nitride based layer. The second Group III-nitride based layer has a bandgap that is less than a bandgap of the first Group III-nitride based layer and has an associated second strain. The second strain has a magnitude that is greater than a magnitude of the first strain. A third Group III-nitride based layer, such as an AlGaN or AlN layer, is on the GaN layer. The third Group III-nitride based layer has a bandgap that is greater than the bandgap of the second Group III-nitride based layer and has an associated third strain. The third strain is of opposite strain type to the second strain. A source contact, a drain contact and a gate contact may be provided on the third Group III-nitride based layer. Nitride based heterojunction transistors having an AlGaN based bottom confinement layer, a GaN based channel layer on the bottom confinement layer and an AlGaN based barrier layer on the channel layer, the barrier layer having a higher concentration of aluminum than the bottom confinement layer, are also provided. Methods of fabricating such transistor are also provided.

Metal nitride deposition by ALD with reduction pulse

Abstract: The present methods provide tools for growing conformal metal thin films, including metal nitride, metal carbide and metal nitride carbide thin films. In particular, methods are provided for growing such films from aggressive chemicals. The amount of corrosive chemical compounds, such as hydrogen halides, is reduced during the deposition of transition metal, transition metal carbide, transition metal nitride and transition metal nitride carbide thin films on various surfaces, such as metals and oxides. Getter compounds protect surfaces sensitive to hydrogen halides and ammonium halides, such as aluminum, copper, silicon oxide and the layers being deposited, against corrosion. Nanolaminate structures incorporating metallic thin films, and methods for forming the same, are also disclosed.

Nitride-based semiconductor light-emitting device and manufacturing method thereof

Abstract: A nitride-based semiconductor light-emitting device and a manufacturing method thereof are provided. The nitride-based light-emitting device includes a first conductivity type nitride-based semiconductor layer, a light-emitting layer and a second conductivity type nitride-based semiconductor layer, that are successively layered above a translucent base. A first conductivity type electrode layer is electrically connected to the first conductivity type nitride-based semiconductor layer, and a second conductivity type electrode layer is electrically connected to the second conductivity type nitride-based semiconductor layer.

Realization of wide electron slabs by polarization bulk doping in graded III–V nitride semiconductor alloys

Abstract: We present the concept and experimental realization of polarization-induced bulk electron doping in III–V nitride semiconductors By exploiting the large polarization charges in the III–V nitrides, we are able to create wide slabs of high-density mobile electrons without introducing shallow donors Transport measurements reveal the superior properties of the polarization-doped electron distributions than comparable shallow donor-doped structures, especially at low temperatures due to the removal of ionized impurity scattering Such polarization-induced three-dimensional electron slabs can be utilized in a variety of device structures owing to their high conductivity and continuously changing energy gap

Method of forming a barrier film and method of forming wiring structure and electrodes of semiconductor device having a barrier film

Abstract: There is provided a method of forming a barrier metal which is designed to be interposed between a metal layer and an insulating layer, both constituting a multi-layered structure of semiconductor device, the method comprising the steps of positioning a substrate having the insulating layer formed thereon at a predetermined position inside a processing vessel forming a processing space, and alternately introducing a gas containing a refractory metallic atom, a gas containing Si atom and a gas containing N atom into the processing vessel under a predetermined processing pressure, thereby allowing a refractory metal nitride or a refractory metal silicon nitride to be deposited on the insulating layer by way of atomic layer deposition.

Realization of wide electron slabs by polarization bulk doping in graded III-V nitride semiconductor alloys

Abstract: We present the concept and experimental realization of polarization-induced bulk electron doping in III-V nitride semiconductors. By exploiting the large polarization charges in the III-V nitrides, we are able to create wide slabs of high density mobile electrons without introducing shallow donors. Transport measurements reveal the superior properties of the polarization doped electron distributions than comparable shallow donor doped structures. The technique is readily employed for creating highly conductive layers in many device structures.

Resonator with seed layer

Abstract: A thin-film resonator having a seed layer and a method of making the same are disclosed. The resonator is fabricated having a seed layer to assist in the fabrication of high quality piezoelectric layer for the resoantor. The resonator has the seed layer, a bottom electrode, piezoelectric layer, and a top electrode. The seed layer is often the same material as the piezoelectric layer such as Aluminum Nitride (AlN).