Papers by Keyword: High Temperature Annealing

Abstract: Studies of the temperature dependence of the electrical properties of glasses show that the high-temperature annealing in glasses observed irreversible processes. These processes lead to changes in electrical conductivity, dielectric permittivity, and hence the electrical capacitance, dielectric loss tangent, and other parameters. Obviously, this is due to structural changes in the glass as a result of high-temperature annealing. In this regard, this paper presents studies of structural and phase transformations in glasses used for the production of microchannel plates in the process of high-temperature annealing in vacuum and in the air atmosphere at different times. The studies were conducted by x-ray phase and X-ray diffraction analysis, as well as X-ray fluorescence elemental analysis.

Abstract: Mechanism of surface roughening caused by the polishing induced subsurface damage on 4^o off-cut 4H-SiC (0001) substrate during thermal etching, CVD epitaxial growth, and the subsequent high temperature annealing was investigated in the wide temperature range of 1000-1800°C. Different from the previous study based on a macroscopic characterization by optical microscopy, microscopic characterization based on a scanning electron microscopy (SEM) was employed in this study. By utilizing the SEM operated under various conditions, disordered step arrangements as well as stacking faults and dislocations were imaged. The obtained results revealed that the SFs cause the fluctuation in the step kinetics, resulting in the step bunching formation during the thermal process.

Abstract: In this study, we investigated the annealing temperature dependence of dislocation extension in an ion-implanted region of a 4H-silicon carbide (SiC) C-face epitaxial layer, revealing that a high temperature annealing led to dislocation formation. We also investigated the current-voltage (I-V) characteristics of a 4H-SiC PIN diode with and without these extended dislocations. We demonstrated that the forward biased I-V characteristics of samples with extended interfacial dislocations have a kink at lower current regions.

Abstract: Phase composition and γ′-phase morphology of a superalloy on based N I-Al doped by high-melting elements in it after ordering annealing hawe been studied by TEM, SEM and electron microdiffraction methods. It is revealed that after annealing superalloy comprises mainly γ′-phase (∼90%). The structure, distribution and morphology of γ′-phase is determined.

Abstract: This article summarises results of structure stability investigation of cast Ni-base and Co-base alloys after prolonged high temperature exposure at 900-1100 °C. Cast Ni (Co)-Cr-W-C alloys are resistant to high-temperature corrosion, due to high chromium content. Their heat resistance is caused by presence of carbides, which are stable at very high temperatures. Carbides precipitate in shape of large plate-like particles or carbide eutectics at casting cell boundaries, thus forming carbide skeleton of the alloy. Carbide morphology and temperature stability depends on chemical composition of the alloy, e.g. carbide content, type and content of carbide-forming elements. Microstructure changes were evaluated by stereological analysis and X ray-spectral microanalysis.

Abstract: Basal Plane Dislocations (BPD) were reduced in 4H-SiC epilayers by high temperature annealing in the range of 1600 °C to 1950 °C using two annealing techniques. Samples annealed at > 1750 °C showed almost complete elimination of BPDs propagating from the substrate. However, surface morphology was degraded for MW annealed samples above 1800 °C, with new BPDs being generated from the surface. A new capping technique was developed along with application of high N₂ overpressure to preserve the surface morphology and avoid formation of new BPDs.

Abstract: In this paper the impact of high temperature annealing on the formation of intrinsic defects in 4H-SiC such as Z_1/2 and EH_6/7 was examined. Therefore, three epitaxial layers with various initial concentrations of the Z_1/2- and EH_6/7-centers (10¹¹ – 10¹³ cm^-3) were investigated. It turns out that depending on the initial defect concentration the high temperature annealing leads to a monotone increase of the Z_1/2- and EH_6/7-concentration in a temperature range from 1600 to 1750°C. For a defined temperature above these values, the resulting defect concentration is independent of the sample’s initial values. Beside the growth conditions themselves such as C/Si ratio the thermal post-growth processing has a severe impact on the carrier lifetime which must be taken into account during device fabrication.

Abstract: Step-terrace structures were observed at on-axis/4o off 4H-SiC {0001} surfaces after Si-vapor etching which we have been supposed as an original technique to planarize and etch the SiC surfaces by utilizing a TaC crucible in temperature ranged from 1600 to 2200 oC. The structures obtained after the Si-vapor etching obviously indicated temperature dependence. There were two types of step-terrace structures in terms of the step height and the shape of the step edges at on-axis surfaces. Step bunched surfaces consisting of full unit cell height (= 1.0 nm) steps with {1-10n} facets at the step edges were observed at 4H-SiC (0001) in lower temperatures below 2000 oC, while smooth isotropic surfaces with half unit cell height (= 0.5 nm) steps and without any stable facets at the step edges were observed at 4H-SiC (0001) in higher temperatures above 2000 oC and in all temperature conditions (1600 - 2200 oC) at 4H-SiC (000-1). Similar tendency was also confirmed at 4o off 4H-SiC {0001} surfaces. From the comparison with 6H-SiC, macro step bunching (~10 nm height) was revealed to be a unique phenomenon at 4H-SiC (0001) surface in the etching.

Abstract: High temperature annealing effects on Oxygen-induced defects formation has been studied by IR-LST, FTIR and TEM techniques. The results show that most defects are amorphous oxygen precipitates and/or dislocations. Ham’s theory has been modified in order to take into account the variations of interstitial oxygen concentration during the formation of precipitates. Comparison between experimental data and simulation shows that the specificity of annealing cycle is to combine both nucleation and growth stages. The morphology and stoechiometry of SiOx precipitates are also studied.

Abstract: As a new graphene functionality applicable to post-implantation high temperature annealing of SiC, a method of in situ formation and removal of large area epitaxial few-layer graphene on 4H-SiC(0001) Si-face is proposed. It is demonstrated that the homogeneous graphene layer formed by Si sublimation can be preserved without the decomposition of the underlying SiC substrate even in the excess of 2000 oC in ultrahigh vacuum. It is due to the existence of the stable (6√3×6√3) buffer layer at the interface. To ensure this cap function, the homogeneity of the interface must be guaranteed. In order to do that, precise control of the initial SiC surface flatness is required. Si-vapor etching is a simple and versatile SiC surface pre/post- treatment method, where thermally decomposed SiC surface is compensated by a Si-vapor flux from Si solid source in the same semi-closed TaC container. While this Si-vapor etching allows precise control of SiC etch depth and surface step-terrace structures, it also provides a “decap” function to remove of the graphene layer. The surface properties after the each process were characterized by AFM and Raman spectroscopy.