SPECIFIC FEATURES OF APPLICATION OF CADMIUM AS A NEUTRON-ABSORBING SCREEN WHILE DOPING SILICON IN A NUCLEAR REACTOR

The gradient of the neutron field in a nuclear reactor and the requirements for the permissible spread of the specific electrical resistance over the volume of the silicon ingot makes it necessary to develop an irradiation device. This is especially true for large silicon ingots. One of the options for reducing the gradient of the neutron flux along the height of the ingot is the use of neutron-absorbing screens in the design of the irradiation device. At the WWR-K reactor, cadmium with a natural isotopic composition is used as a neutron-absorbing screen material. The paper presents the results of a study of an irradiation device with a cadmium screen. The effect of a cadmium screen on the neutron-physical characteristics of an irradiation device for silicon doping is shown.

Defect controls by silicon doping in non-polar a-plane AlGaN epi-layers

Deposition of high-quality Si-doped crystalline AlGaN layers, especially non-polar-grown AlGaN layers, is critical and remains difficult in preparing AlGaN-based light-emitting diodes (LEDs), as the Si-doping-induced variations of crystalline structures are still under exploration. In this work, structural characterizations of Si-doped AlxGa1−xN layers were carried out by associating with examination of their carrier recombination behaviors in photoluminescence (PL) processes, to clarify the physical mechanism on how Si doping controls the formation of structural defects in AlGaN alloy. The obtained results showed that Si doping induced extrinsic shallow donor states and increased the densities of point defects like cation vacancies. On the contrary, Si doping suppressed formation of line defects like dislocations and planar defects like stacking faults with suitable doping concentration. These results may guide further improvement of UV-LEDs based on AlGaN alloy.

Calculation of neutronic characteristics in different reflector materials with a 15-MWt reactor core using VVR-KN fuel type

VVR-KN is one of the low enriched fuel types intended for a research reactor of a newCentre for Nuclear Energy Science and Technology (CNEST) of Viet Nam. As a part of design orientation for the new research reactor, the calculations of neutronic characteristics in a reactor core reflector using different materials were carried out. The investigated core configuration is a 15-MWt power loaded with VVR-KN fuel assemblies and surrounded by a reflector using beryllium, heavy water or graphite respectively. MCNP5 code together with up-to-date nuclear data libraries were used for these calculations. This paper presents the calculation results of neutron energy spectrum, neutron spatial distribution in the reflector using the above-mentioned materials. Besides, neutronic characteristics calculated for silicon doping irradiation holes in the reflector are also presented and the utilization capabilities of different reflector materials are discussed.

Modification of Cathode Material Lithium Iron Phosphate by Silicon Doping Using Solid State Reaction

Lithium iron phosphate (LiFePO4) based material is one of the most prospective candidates as a cathode material in lithium-ion batteries because of its lower cost, safer, and environmental benignity compared to lithium cobalt oxide (LiCoO2), which is commonly used for lithium-ion batteries manufacturing. However, its low conductivity is the obstacle of this material to solve, so that modification with the addition of silicon (Si) is expected to improve the electrochemical performance. Meanwhile, solid state reaction is considered simple and effective in LiFePO4 crystal growth process. Therefore, Si-doped LiFePO4 using solid state reaction in this research aims to study its structure and morphology as well as the effect of adding Si to its conductivity. The synthesis began with mixing LiH2PO4, Fe2O3, carbon black, and six-mole ratio variation of Si to LiFePO4 using agate with ethanol: acetone addition then dried in an oven at 80°C and heated at 550°C in a furnace for 6 hours under argon atmosphere and sintering temperature of 870°C for 16 hours with the same condition. The sample of 3% mole ratio performed the highest conductivity of all variations with 3.01 x 10-6 S.cm-1, and was identified as Li0.93Fe1.07P0.93O4Si0.7 with orthorhombic structure, Pnma space group (Ref. Code: ICSD 98-016-1792) with the highest peak at 2θ = 35.556° from XRD analysis with rectangular-like shape particle.

Charge Density Based Small Signal Modeling for InSb/AlInSb Asymmetric Double Gate Silicon Substrate HEMT for High Frequency Applications

The Asymmetric Double Gate Silicon Substrate HEMT(ADG-Si-HEMT) is proposed in this article to analyse the carrier concentration and intrinsic small signal parameters for the heterostructure of the InSb/AlInSb silicon wafer DG-HEMT device. When the top and bottom gates are biased with different gate voltages, the HEMTs act as a three-port system and the device called Asymmetric Double Gate HEMT. The modulation of back-channel charge density due to the front gate voltage is analyzed with the position of quasi-Fermi energy levels(Ef). Also, the small signal model is obtained for various parameters like cut off frequency, gate to source capacitance and transconductance. The effects of the following parameters like delta doping, width of Silicon doping layer and various top and bottom gate voltages are analyzed to get enhanced device operation. The transconductance 2390 Sm/mm for Vfg=0.2V and cut off frequency around 197 GHz for Vbg=0.3 are obtained. All the analytical results are compared with Sentaurus 3-D TCAD simulation results. The asymmetric biasing technique offers various mixed application due to modulation in threshold voltage and modulating carrier density in dual channels.

Quantification of Trace-Level Silicon Doping in Al x Ga1–xN Films Using Wavelength-Dispersive X-Ray Microanalysis

Wavelength-dispersive X-ray (WDX) spectroscopy was used to measure silicon atom concentrations in the range 35–100 ppm [corresponding to (3–9) × 1018 cm−3] in doped Al x Ga1–xN films using an electron probe microanalyser also equipped with a cathodoluminescence (CL) spectrometer. Doping with Si is the usual way to produce the n-type conducting layers that are critical in GaN- and Al x Ga1–xN-based devices such as LEDs and laser diodes. Previously, we have shown excellent agreement for Mg dopant concentrations in p-GaN measured by WDX with values from the more widely used technique of secondary ion mass spectrometry (SIMS). However, a discrepancy between these methods has been reported when quantifying the n-type dopant, silicon. We identify the cause of discrepancy as inherent sample contamination and propose a way to correct this using a calibration relation. This new approach, using a method combining data derived from SIMS measurements on both GaN and Al x Ga1–xN samples, provides the means to measure the Si content in these samples with account taken of variations in the ZAF corrections. This method presents a cost-effective and time-saving way to measure the Si doping and can also benefit from simultaneously measuring other signals, such as CL and electron channeling contrast imaging.