Boron doping of silicon rich carbides: Electrical properties

Boron doped multilayers based on silicon carbide/silicon rich carbide, aimed at the formation of silicon nanodots for photovoltaic applications, are studied. X-ray diffraction confirms the formation of crystallized Si and 3C-SiC nanodomains. Fourier Transform Infrared spectroscopy indicates the occurrence of remarkable interdiffusion between adjacent layers. However, the investigated material retains memory of the initial dopant distribution. Electrical measurements suggest the presence of an unintentional dopant impurity in the intrinsic SiC matrix. The overall volume concentration of nanodots is determined by optical simulation and is shown not to contribute to lateral conduction. Remarkable higher room temperature dark conductivity is obtained in the multilayer that includes a boron doped well, rather than boron doped barrier, indicating efficient doping in the former case. Room temperature lateral dark conductivity up to 10^?3 S/cm is measured on the multilayer with boron doped barrier and well. The result compares favorably with silicon dioxide and makes SiC encouraging for application in photovoltaic devices.     

Formation of buried insulating layers by high dose oxygen implantation under controlled temperature conditions

A specially designed sample holder was used to form SOI structures by high dose oxygen implantation under controlled temperature conditions. This system uses a layer of molten tin to provide a good thermal contact between the silicon wafer and a resistively heated support. The layers formed under these conditions were characterized by RBS and XTEM. After annealing at 1150°C for 2 h the only remaining defects in the top silicon layers are dislocations with a density of less than 10⁷ cm^?2 and SiO₂ precipitates. Annealing at 1185°C for 6 h does not change the density of dislocations but leads to the formation of a 200 nm thick silicon layer free of SiO₂ precipitates, suitable for VLSI processing without growing an epitaxial layer.     

Notch Sensitivity of Fatigue Behavior of a Hi-Nicalon™/SiC-B4C Composite at 1,200 °C in Air and in Steam

The effect of holes on the fatigue life of a non-oxide ceramic composite processed via chemical vapor infiltration (CVI) was examined at 1,200 °C in laboratory air and in steam. The effect of holes on tensile strength at 1,200 °C was also evaluated. The composite comprised laminated woven Hi-Nicalon? fibers in an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Unnotched specimens and specimens with a center hole having a radius to width ratio of 0.24 were tested in tension-tension fatigue at 0.1 Hz and at 1.0 Hz. The fatigue stresses ranged from 100 to 140 MPa in air and in steam. Fatigue run-out was defined as 10⁵ cycles at 0.1 Hz and as 2?×?10⁵ cycles at 1.0 Hz. The net-section strength was less than the unnotched ultimate tensile strength. Comparison of notched and unnotched data also revealed that the fatigue performance was notch insensitive in both air and steam environments. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Ladungsträger‐Tiefenprofilierung an ultra‐flachen pn‐Übergängen

Charge carrier depth profiling on ultrashallow pn‐junctions The Stepwise Oxidation Profiling (SWOP) technique has been applied to charge carrier depth profiling on boron ion implanted silicon. The procedure works by altering between electrical sheet resistance measurements on van‐der‐Pauw (VDP)‐ structures and Si layer removal by electrochemical anodic oxidation. It was shown that the SWOP profiles are matching well with SIMS reference measurements, and that a depth resolution of ≤ nm and a detection limit of 1·10¹⁶cm^?3 was achieved.     

Structure and properties of strengthening layer on Hardox 450 steel

The microstructure and microhardness distribution in the surface of low-carbon Hardox 450 steel coated with alloyed powder wires of different chemical compositions are studied. It is shown that the microhardness of 6–8?mm-thick surfaced layer exceeds that of base metal by more than two times. The increased mechanical properties of surfaced layer are caused by the submicro and nanoscale dispersed martensite, containing the niobium carbides Nb₂C, NbC and iron borides Fe₂B. In the bulk plates, a dislocation substructure of the net-like type with scalar dislocation density of 10¹¹?cm^?2 is observed. The layer surfaced with the wire containing B possesses highest hardness. The possible mechanisms and temperature regimes of niobium and boron carbides in surfacing are discussed.     

Lattice parameter study of silicon uniformly doped with boron and phosphorus

Powder and single-crystal X-ray techniques have been employed to obtain precise lattice parameters of silicon uniformly doped with boron or phosphorus. Good agreement is found between the two methods. Previous accurate determination of the CuKα₁, effective wavelength has yielded λ=1.540621±0.000006 Å. Particular care has been devoted to the chemical and electrical characterization of the alloys, whose maximum dopant concentrations were 8×10¹⁹ atoms cm^?3 for P and 4.4×10²⁰ atoms cm^?3 for B. A linear dependence of lattice parameter on concentration has been found for P in the whole examined range, while for B a deviation from the linear trend starts at about 2.25×10²⁰ atoms cm^?3. Tetrahedral radii are found to be 1.176 Å for pure Si, 1.07 Å and 0.91 Å respectively for dissolved substitutional P and B. Values of the linear lattice contraction coefficient, volume size factor, Vegard's law factor and elastic strain energy in both alloys are reported and discussed. The deviation from linear trend in borondoped alloys is analysed and it is shown that the phenomenon is insensitive to heattreatments and does not depend on the degree of ionization of boron atoms.     

Diffusion of Pb in (100) Si under electron beam annealing following dual ion implantations of Pb/Ne, Pb/O and Pb/N

(100) Si was dual-implanted with the ions Pb⁺/²²Ne⁺ (7 and 30 keV), Pb⁺/¹⁶O⁺ (7 and 26 keV) and Pb⁺/¹⁴N⁺ (7 and 24 keV) to peak concentrations of typically 10 at.%. The implanted samples were then electron beam annealed at 900 °C for 30 s with a temperature gradient of 5 °C s⁻¹ under high vacuum conditions. Channelled RBS measurements performed with 1.5 MeV ⁴He⁺ ions showed that annealing of the Pb/Ne and Pb/O samples resulted in an almost complete recrystallisation of the amorphous layers caused by the ion implantations and a total loss of the implanted Pb. For the Pb/Ne samples the Ne diffused out to leave a rough surface sprinkled with deep craters; for the Pb/O samples some SiO₂ formed below the surface. In contrast, for the Pb/N samples most of the amorphous layer survives annealing and almost all the Pb is retained. A striking feature is that annealing causes the Pb to diffuse away from the surface to be trapped in a deep diffusion sink provided by the implanted N. XRD analyses exhibited Pb (111) and Pb (220) reflections suggesting that Pb nanoclusters have grown in the understoichiometric silicon nitride layer. These structures offer an interesting opportunity for controlled carbon nanotube (CNT) growth on silicon nitride.     

Structural investigations of RTA boron-doped thin a-Si layers

The structural changes in as- sputtered thin a-Si layer, and after boron doping with rapid thermal annealing are investigated by transmission electron microscopy. Stable hexagonal amorphous/crystalline series of SiO₂ structures, as signed as SiO₂ (SnO₂-V), not revealed in high temperature SiO₂ layers, are observed in all films investigated. Different types of crystalline and high ordered SiO₂ structures are obtained in the BSG film, used for doping. Boron penetration in the a-Si layer starts the crystallization at B/Si ratios lower than 10⁻³. RTA process leads to inhomogeneous disordered polycrystalline silicon layer, with large areas of poly-and monocrystalline silicon, coexisting with various crystalline SiO₂ structures. Faster crystallization and larger monocrystalline silicon regions are observed at higher temperatures and longest durations of the annealing process.     

Diffusion of copper in thin TiN films

The diffusivity of copper in thin TiN layers was determined in specimens prepared by r.f. sputtering a copper (80 nm) layer onto a TiN (200 nm) layer on sapphire and silicon substrates. Specimens were isothermally heat treated at 608, 635 and 700 °C at pressures lower than 2 × 10^?6 Pa; they were compositionally analyzed by Rutherford backscattering spectroscopy and Auger sputter profiling; and they were microstructurally characterized by transmission electron microscopy and electron diffraction. The diffusivity D = 9 × 10⁷cm²s^?1exp(?427 kJmol^?1/RT) from 608 to 700 °C. The mechanisms of copper diffusion were not bulk processes, but they were probably processes involving primarily grain boundaries in the TiN. This very low diffusivity at these temperatures makes TiN/Cu an excellent candidate for a high temperature metallization for silicon solar concentrator cells.     

Fast divalent ion conduction in Ba++, Cd++ and Sr++ beta″ aluminas

Single crystals of Ba⁺⁺, Cd⁺⁺ and Sr⁺⁺ beta″ alumina were prepared from sodium beta″ alumina by ion exchange. The conductivities of these divalent ion solid electrolytes exceed 10^?3 (ohm-cm)^?1 at 300°C. These compounds appear to exhibit fast divalent ion motion at moderate temperatures.     

Die Ausbildung von Oxidschutzschichten auf verschiedenen Ni-Cr-Fe-Legierungen bei unterschiedlichen Sauerstoffpartialdrucken

The growth of the oxide protective layer on different Ni-Cr-Fe-alloys with variation of oxygen partial pressure High temperature alloys e.g. Incoloy 800 H, Hastelloy X and Ni75Cr25 model alloy are in-situ oxidized with variation potentials oxidation of PO₂ = 4,41 × 10^?19 bar, PO₂ = 4,41 × 10^?17 bar and PO₂ = 176 × 10^?16 bar by temperature, 800°. The behaviour of the scales which are oxidized at different oxidizing atmospheres has been investigated in this work, with deuterium permeation. The test of scales as corrosion barrier had been done in sulfidizing atmospheres with PS₂ = 1,82 × 10^?7 bar. The microstructure of the oxide layers has been investigated with Light Microscopy (LM), Scanning Electron Microscopy (SEM), Analytical Transmission Electron Microscopy (ATEM) and High Resolution Transmission Electron Microscopy (HRTEM). It is found that the deuterium permeation measurement can be correlated as a method for characterization corrosion layer at high temperature alloys. The structure of the oxide layer, the influence of sulfidizing atmospheres, additions of small amounts of reactive elements such as Ti before oxidation, the interface structure between oxide layers and matrix, as well as crystal defects and grain boundaries is explainable.     

Amorphous silicon carbide heterojunction solar cells on p-type substrates

The performance of silicon heterojunction (SHJ) solar cells is discussed in this paper in regard to their dependence on the applied amorphous silicon layers, their thicknesses and surface morphology. The emitter system investigated in this work consists of an n-doped, hydrogenized, amorphous silicon carbide a-SiC:H(n) layer with or without a pure, hydrogenized, intrinsic, amorphous silicon a-Si:H(i) intermediate layer. All solar cells were fabricated on p-type FZ-silicon and feature a high-efficiency backside consisting of a SiO₂ passivation layer and a diffused local boron back surface field, allowing us to focus only on the effects of the front side emitter system. The highest solar cell efficiency achieved within this work is 18.5%, which is one of the highest values for SHJ-solar cells using p-type substrates. A dependence of the passivation quality on the surface morphology was only observed for solar cells including an a-Si:H(i) layer. It could be shown that the fill factor suffers from a reduction due to a reduced pseudo fill factor for emitter thicknesses below 11 nm due to a lower passivation quality and/or a higher potential for shunting thorough the a-Si emitter to the crystalline wafer with the conductive indium tin oxide layer. Furthermore, the influence of a variation of the doping gas flow (PH₃) during the plasma enhanced chemical vapor deposition of the doped amorphous silicon carbide a-SiC:H(n) on the solar cell current-voltage characteristic-parameter has been investigated. We could demonstrate that a-SiC:H(n) shows in principle the same dependence on PH₃-flow as pure a-Si:H(n).     

Effects of annealing on the damage morphologies in BF 2 + ion implanted (1 0 0) silicon

The effects of annealing on the damage morphologies and impurity redistributions in BF ₂ ⁺ ion implanted (1 0 0) silicon were studied using secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM) and Rutherford backscattering (RBS) ion beam channelling technique. An amorphized silicon layer and a heavily-damaged crystal layer containing a high density of point-defect clusters, are formed on the silicon wafer by the ion implantation. SIMS depth profiles of both boron and fluorine are almost Gaussian distribution. Both furnace annealing and rapid thermal annealing cause recrystallization of the amorphized layer and formation of dislocation loop bands out of the point defects. SIMS depth profiles for both impurities show anomalous double peaks at the same depths. These facts suggest that the primary peak is due to the peak of the Gaussian distribution and the secondary peak due to the gettering effects of residual dislocation loop band.     

SIMS analysis of ultrathin implanted arsenic layers in silicon

A new regime of secondary ion mass spectrometry (SIMS) is proposed, which allows a depth resolution of λ=1.4 nm to be achieved. The profiles of arsenic implanted into silicon, measured using this regime on a Cameca IMS-4f microprobe, were close to the true distributions. SIMS profiling of the samples of silicon implanted with 30-keV As⁺ ions to a total dose of (1.25–3.13)×10¹³ cm^?2 through a 20-nm-thick thermal oxide layer showed the presence of a sharp peak of arsenic accumulated at the oxide/silicon interface, which is explained by the diffusion of arsenic to this interface as a result of annealing.     

Structural perfection of heteroepitaxial silicon layers grown on sapphire by sublimation-source molecular beam epitaxy

Structurally perfect, single-crystal silicon layers have been grown on \((1\overline 1 02)\) sapphire by sublimation-source molecular beam epitaxy. Electron and x-ray diffraction data demonstrate that silicon-on-sapphire epitaxy occurs at substrate temperatures from 550 to 850°C. As the thickness of the layers decreases from 1.0 to 0.2 μm, their structural perfection degrades. In the layers grown at 600°C, the density of nucleation sites in the initial stages of growth is ? 5 × 10⁹ cm^?2.     

Comment on the dielectric breakdown properties,current density-voltage and capacitance-voltage characteristics of ion-beam-synthesized Si3N4 layers

Some recent work by Yadav and Joshi on ion-beam-synthesized Si₃N₄ layers has suggested that below the nitride layer an amorphous silicon layer is formed. Electrical conduction through the layers was ascribed to space-charge-limited conduction.It is shown that a fuller analysis of the published capacitance-voltage characteristics indicates that the nitride layer is of approximate thickness 1000 Å, while the amorphous silicon layer may either be absent or of thickness up to 2.3 μm, depending on the annealing conditions. It is confirmed that the current density-voltage characteristics indicate that space-charge-limited conduction takes place, and it is also shown that for a single discrete trapping level the trapping concentration is in the range from 3.3 x 10¹⁹ to 3.6 x 10²⁴ m^-3 for the amorphous silicon and from 3.4 x 10²² to 3.7 x 10²⁷ m^-3 for the nitride; if trapping is via traps exponentially distributed in energy below the conduction band edge the trapping concentrations are 8 x 10²⁷ m^-3 for the amorphous silicon and 1.4 x 10³⁰ m^-3 for the nitride. Although the latter type of trapping distribution is often observed in amorphous insulating layers, it is concluded that the high trapping concentrations calculated in the present case are unlikely to be realistic and that a more complex type of trapping distribution is probably responsible for the effects observed.     

Transfer of thin Si layers by cold and thermal ion cutting

We have used the crack-opening method to study the mechanical exfoliation behavior in hydrogen-implanted and bonded Cz Si. We found that the crystal orientation and boron doping influence the temperature required for mechanical layer transfer. Boron implantation at doses >10¹³ cm^–2 reduces the annealing temperature needed for mechanical exfoliation. The boron-doped epilayers followed similar exfoliation behavior as the boron-implanted samples. No lowering of the exfoliation temperature was observed for compensated and arsenic-doped Si layers. The hydrogen implantation converted the silicon wafer surface from p-type to n-type. The as-transferred Si layer was also found to be n-type after annealing at 200–450 °C. The p-type conductivity was restored upon annealing at around 600 °C. We believe that this conductivity conversion is due to the combined effect of ion-enhanced thermal donors and the presence of H-related shallow donors in the implanted layer. The p-type conductivity is restored at higher temperatures following the dissociation of the thermal donors and the out-diffusion of hydrogen. We also report that a good-quality silicon on glass layer can be obtained by the bonding and ion-cutting processes.     

The formation of SiO2 films on silicon by high dose oxygen ion implantation

High dose oxygen ion implantation into silicon at 30 keV was performed to produce SiO₂ surface layers.The oxygen profile, stoichiometry and volume swelling were studied by Rutherford backscattering at doses of up to 2 × 10¹⁸cm^?2 and for various current densities. The surface structure and lateral homogeneity of the inslation properties were investigated by scanning electron microscopy and the liquid crystal technique respectively. By means of current-voltage and capacitance-voltage measurements the electrical properties of the layers produced were determined.A qualitative model of the formation of SiO₂ during high dose oxygen implantation into silicon is proposed. Blistering caused by implantation at high current densities leads to oxygen losses and to conductive channels in the dielectric layer. Except for their interface properties the SiO₂ films produced are comparable with thermal oxides.     

Shear performance of microscale ball grid array structure Sn–3.0Ag–0.5Cu solder joints with different surface finish combinations under electro-thermo-mechanical coupled loads

The shear performance and fracture behavior of microscale ball grid array structure Sn–3.0Ag–0.5Cu solder joints with different substrate surface finishes (Cu with organic solderability preservatives and electroless Ni/immersion Au) combinations under electro-thermo-mechanical (ETM) coupled loads with increasing current density (from 1.0?×?10³ to 6.0?×?10³ A/cm²) were systematically investigated by experimental characterization, theoretical analysis, and finite element simulation. The results reveal that the shear strength varies slightly with different surface finish combinations, initially increasing and then decreasing as the current density is increased. Moreover, the increase in current density shifts the fracture location from the solder matrix to the interface between solder and intermetallic compound (IMC) layer, resulting in a ductile-to-brittle transition. The interfacial fracture is triggered by electric current crowding at the groove of the IMC layer and driven by the mismatch strain at the solder/IMC layer interface.

     

Wafer-Scale Single Crystal Hexagonal Boron Nitride Layers Grown by Submicron-Spacing Vapor Deposition

The direct growth of wafer-scale single crystal two-dimensional (2D) hexagonal boron nitride (h-BN) layer with a controllable thickness is highly desirable for 2D-material-based device applications. Here, for the first time, a facile submicron-spacing vapor deposition (SSVD) method is reported to achieve 2-inch single crystal h-BN layers with controllable thickness from monolayer to tens of nanometers on the dielectric sapphire substrates using a boron film as the solid source. In the SSVD growth, the boron film is fully covered by the same-sized sapphire substrate with a submicron spacing, leading to an efficient vapor diffusion transport. The epitaxial h-BN layer exhibits extremely high crystalline quality, as demonstrated by both a sharp Raman E_2g vibration mode (12 cm⁻¹) and a narrow X-ray rocking curve (0.10°). Furthermore, a deep ultraviolet photodetector and a ZrS₂/h-BN heterostructure fabricated from the h-BN layer demonstrate its fascinating properties and potential applications. This facile method to synthesize wafer-scale single crystal h-BN layers with controllable thickness paves the way to future 2D semiconductor-based electronics and optoelectronics.