Influence Of Silicon Doping Research Articles

Influence of Silicon-Doping in n-AlGaN Layer on the Optical and Electrical Performance of Deep Ultraviolet Light-Emitting Diodes

The influence of two different methods of silicon doping in AlGaN layer, that is, modulation-doping (MD) and delta-doping (DD), on the optical and electrical performance of deep ultraviolet light-emitting diodes (DUV-LEDs) has been investigated. Both the photoluminescence and electroluminescence intensities in the Si-DD structure are stronger than those obtained by the Si-MD method, while the forward voltage and reverse leakage current are slightly smaller in the DD structure than that in the MD structure. Compared with the MD structure, the DD structure shows higher capacitance-voltage characteristics. This study suggests that the DD method can improve the optical and electrical performance of DUV-LEDs.

Influence of silicon doping on internal quantum efficiency and threshold of optically pumped deep UV AlGaN quantum well lasers

The influence of silicon doping on optically pumped AlGaN quantum well (QW) lasers has been analyzed. Either the QWs, quantum barriers, or the whole heterostructure were doped with Si concentrations between 6 × 1016 and 1 × 1019 cm−3. When the QWs are doped up to 5 × 1017 cm−3, laser threshold is reduced and internal quantum efficiency is increased most probably due to a reduction of group-III-vacancies during growth. Higher Si concentrations in the wells can increase the density of group-III-vacancies causing an increased laser threshold. High concentrations can also enhance band gap inhomogeneities and the free carrier density, which improves the internal quantum efficiency measured by photoluminescence. Doping of all layers with a Si concentration of 1 × 1019 cm−3 deteriorates the QW quality, most probably because the silicon acts as an anti-surfactant reducing and delaying Ga incorporation.

Influence of doping in InP buffer on photoluminescence behavior of InPBi

InP1−xBix epilayers with 1.0% bismuth concentration were grown on InP(001) substrates by gas-source molecular beam epitaxy. Silicon and beryllium were doped into the InP buffer layer, and their influences on the photoluminescence (PL) emission of InPBi were investigated. The PL emission of InPBi was found to be intensified by beryllium doping into the InP buffer layer. However, there was no influence of silicon doping. To investigate the reason for the PL intensity enhancement of InPBi, the carrier transport behavior at the interface was also discussed.

The Influence of Silicon Doping on Electrical Characteristics of Solution Processed Silicon Zinc Tin Oxide Thin Film Transistor

Effect of silicon doping into ZnSnO systems was investigated using solution process. Addition of silicon was used to suppress oxygen vacancy generation. The transfer characteristics of the device showed threshold voltage shift toward the positive direction with increasing Si content due to the high binding energy of silicon atoms with oxygen. As a result, the carrier concentration was decreased with increasing Si content.

Si-TCP synthesized from "Mg-free" reagents employed as calcium phosphate cement

The influence of silicon doping on calcium phosphate cement were explored in this work. α-TCP and Si-α-TCP were prepared by solid state reaction employing Mg-free CaHPO4, CaCO3 and CaSiO3 as precursors. It was possible to obtain TCP powders with low contents of β phase as contaminant. Cement liquid phase was an aqueous solution containing 2.5 wt. (%) of Na2HPO4 and 1.5 wt. (%) of citric acid. The liquid-to-powder ratio was 0.6 mL.g-1. Chemical, physical and mechanical properties of the cement samples were determined by means of XRD, FTIR, XRF, compressive strength and SEM. The calcium phosphate cements obtained achieved satisfactory properties; however, Si-α-TCP presented a decrease on the rate of setting reaction.

Si-tricalcium phosphate cement: preparation, characterization and bioactivity in SBF

There are evidences considering the effectiveness of Si on enhancing biological properties of calcium phosphates; however, there are not many works relating to the Si-alpha-TCP bone cement. The influence of silicon doping on the properties of Α-TCP cement was analyzed. Si-TCP was obtained by a solid state reaction employing CaCO3, CaHPO4 and CaSiO3 and powder was analyzed by XRD, FTIR, XRF and BET specific area. Cement samples were analyzed for their surface of fracture morphology, mechanical resistance and SBF bioactivity. Cement mechanical resistance was not satisfactory for biomedical application; nonetheless, sample's surface was coated by an apatite layer after immersion in SBF. Notwithstanding, to ensure that silicon is the element responsible for increasing the material's bioactivity it is necessary to evaluate the in vivo performance of the bone cement obtained in this work.

CHARACTERISTICS OF DLC FILMS INCORPORATED HMDS BY RF PECVD

Silicon incorporated diamond-like carbon films up to 6.2 at. % (DLC- Si ) were deposited onto a high speed steel samples by using a radio frequency plasma-enhanced chemical vapor deposition method. The influence of silicon doping on chemical composition, bonding structure, hardness, and adhesion of DLC films was investigated. Hexamethyldisilane ( HMDS ) gas was used as a silicon source with Ar carrier gas ranging from 0 to 15 sccm. Also, the mixtures of methane ( CH 4) and Ar gases were used as precursor gases. The addition of silicon into the DLC film was found to lead an increase of bonding ratio ( sp 3/ sp 2), hardness and critical adhesion

The mechanical and biocompatibility properties of DLC-Si films prepared by pulsed DC plasma activated chemical vapor deposition

Films of diamond-like carbon containing up to 22 at.% silicon (DLC-Si) were deposited on to silicon substrates by low-frequency pulsed DC plasma activated chemical vapor deposition (PACVD). The influence of silicon doping on deposition rate, composition, bonding structure, hardness, stress, surface roughness and biocompatibility was investigated and correlated with silicon content. A mixture of methane and tetramethylsilane (TMS) was used for the deposition of DLC-Si films at a pressure of 200 Pa. The deposition rate increased with increasing TMS flow. The addition of silicon into the DLC film leads to an increase of sp 3 bonding, as measured by Raman spectroscopy, and also resulted in lower stress and hardness values. The RMS surface roughness of the films was measured by atomic force microscopy and increased from 0.35 nm for DLC to 6.7 nm for DLC-Si (14 at.% Si) due to the surface etching by the H atoms. Biocompatibility tests were performed using MG-63 osteoblast-like cell cultures that were left to grow for 3 days and their proliferations were assessed by scanning electron microscopy. The results indicated a homogeneous and optimal tissue integration for both the DLC and the DLC-Si surfaces. This pulsed PACVD technique has been shown to produce biocompatible DLC and DLC-Si coating with potential for large area applications.

Influence of silicon doping on the nanomorphology and surface chemistry of a wood-based carbon molecular sieve

Carbon–silica molecular sieves were prepared by carbonization of Scotch fir ( Pinus sylvestris) after impregnation with aqueous waterglass (Na x Si y O z , where x, y and z may take a range of values). Compared to Si-free samples, doping significantly modifies the structure that forms during the carbonization process. For carbonization temperatures between 600 °C and 1000 °C, doped samples shrink less than undoped samples, indicating increased mechanical strength. The specific surface area and pore volume develop in a combined self-activation and chemical vapour deposition (CVD) process. Nevertheless, the presence of the sodium silicates limits self-activation and thus reduces the porosity. Doping drastically reduces the specific surface area, measured both by gas adsorption and small angle X-ray scattering. The latter technique demonstrates that in both doped and undoped samples the specific surface area is isotropic. X-ray photoelectron spectroscopy (XPS) reveals that the spatial distribution of Na and Si atoms within the samples are not identical. The open honeycomb structure, conserved during the heat treatment from the original wood, provides easy access for gas adsorption and separation applications. The ratios of the microporous diffusion time constants of N 2 and O 2 from frequency response (FR) measurements gave separation factors 3.0, 4.3, 2.7 and 1.3 for samples prepared at 600 °C, 700 °C, 800 °C and 900 °C, respectively.

Electronic properties of a semiconducting oligomer/silicon (111) interface: Influence of silicon doping

The interface formation between a semiconducting oligomer and the p-doped Si(111) surface was investigated by X-ray and ultraviolet photoelectron spectroscopies (UPS) and the results were compared to the same oligomer/Si (n-doped) interface. The position of the energy levels of the bulk oligomer film was identical in both interfaces, while differences appeared at the first steps of the interface formation. The band bending at the interfaces was assessed from X-ray photoelectron spectra while the interfacial dipoles from the UPS results. A ∼0.30eV dipole layer was observed at the oligomer/Si (p-doped) interface whereas the oligomer/Si (n-doped) interface is dipole free. The valence-band offset between silicon and the oligomer was found ∼0.40eV in both cases.

Interaction of plasma-facing materials with air and steam

In the design of ITER-FEAT, several candidate materials are foreseen for plasma-facing components of the divertor (tungsten, carbon fibre-reinforced composites (CFC), molybdenum) and the first wall (beryllium). In the view of accidental scenarios such as a loss of coolant accident or a loss of vacuum accident the reaction between these materials and steam or air remains a safety concern. To provide kinetic data, describing the chemical reactivity of plasma-facing materials in air and steam, we used coupled thermogravimetry/quadrupole mass spectrometry. In this paper we present the results of a screening investigation that compares the oxidation rates of tungsten, molybdenum, CFC and beryllium in the temperature range 300–700 °C. From the thermogravimetry and mass spectrometry results we obtained the reaction rates as a function of temperature. For the metals tungsten, molybdenum and beryllium, a transition is observed between protective oxidation at lower temperatures and non-protective oxidation at higher temperatures. This transition temperature lies in the range 500–550 °C for tungsten and molybdenum, which is lower than for beryllium. At above temperatures 550 °C, the oxides formed on molybdenum and tungsten volatilise. This increases the oxidation rate dramatically and can lead to mobilisation of activation products in a fusion reactor. We also performed experiments on both undoped CFC and CFC doped with 8–10% silicon. The influence of silicon doping on the chemical reactivity of CFC's in air is discussed.

Crystal defects in vertical cavity epitaxial structures on GaAs investigated by X-ray methods

The influence of doping on the generation of misfit dislocations in AlAs/GaAs Bragg reflectors and vertical cavity surface emitting laser structures grown by molecular beam epitaxy has been investigated by X-ray topography and diffractometry. While carbon doping reduces the lattice constants of AlAs and GaAs considerably, the influence of silicon doping is less clear. However, silicon is well known to reduce the mobility of dislocations. In the present work it is shown that both dopants prevent the relaxation of 3 μm thick Bragg reflectors and reduce considerably the density of misfit dislocations in complete laser structures. Laser structures with a beryllium-doped Bragg reflector, however, contain a high density of misfit dislocations for a wide range of growth temperatures. These dislocations are distributed over the whole layer stack; their topographic contrasts vary along the dislocation lines. Contrast simulations show that these changes may be attributed to the depth location of the defects in the stack.