Mg2Si Layer Research Articles

Magnetic Field and Temperature Dependence of the Transmission Defect Mode in One-Dimensional Photonic Crystals Containing CoSb3 and Mg2Si Layers

Magnetic Field and Temperature Dependence of the Transmission Defect Mode in One-Dimensional Photonic Crystals Containing CoSb3 and Mg2Si Layers

Effect of Sacrificial Mg2Si Layers and Kinetic Parameters on the Growth, Structure, and Optical Properties of Thin Ca2Si Films on Silicon Substrates

Effect of Sacrificial Mg2Si Layers and Kinetic Parameters on the Growth, Structure, and Optical Properties of Thin Ca2Si Films on Silicon Substrates

High-performance broadband photoresponse of self-powered Mg2Si/Si photodetectors

Infrared optoelectronic devices are capable of operating in harsh environments with outstanding confidentiality and reliability. Nevertheless, suffering from the large band gap value, most semiconductor materials are difficult to detect infrared light signals. Here, Mg2Si/Si heterojunction photodetectors (PDs), which possess the advantages of low-cost, easy process, environmental friendliness, and compatibility with silicon CMOS technology, have been reported with a broadband spectral response as tested from 532 to 1550 nm under zero-bias. When the incident light wavelength is 808 nm, the Mg2Si/Si photodetector (PD) has a responsivity of 1.04 A W−1 and a specific detectivity of 1.51 × 1012 Jones. Furthermore, we find that the Ag nanoparticles (Ag_NPs) assembled on the Mg2Si layer can greatly improve the performance of the Mg2Si/Si PD. The responsivity and specific detectivity of Mg2Si/Si device with Ag_NPs under 808 nm illumination are 2.55 A W−1 and 2.60 × 1012 Jones, respectively. These excellent photodetection performances can be attributed to the high-quality of our grown Mg2Si material and the strong built-in electric field effect in the heterojunction, which can be further enhanced by the local surface plasmon effect and local electromagnetic field induced by Ag_NPs. Our study would provide significant guidance for the development of new self-powered infrared PDs based on silicon materials.

Simulation Study on the Effect of Doping Concentrations on the Photodetection Properties of Mg2Si/Si Heterojunction Photodetector

To develop and design an environmentally friendly, low-cost shortwave infrared (SWIR) photodetector (PD) material and extend the optical response cutoff wavelengths of existing silicon photodetectors beyond 1100 nm, high-performance silicon-compatible Mg2Si/Si PDs are required. First, the structural model of the Mg2Si/Si heterojunction was established using the Silvaco Atlas module. Second, the effects of the doping concentrations of Mg2Si and Si on the photoelectric properties of the Mg2Si/Si heterojunction PD, including the energy band, breakdown voltage, dark current, forward conduction voltage, external quantum efficiency (EQE), responsivity, noise equivalent power (NEP), detectivity, on/off ratio, response time, and recovery time, were simulated. At different doping concentrations, the heterojunction energy band shifted, and a peak barrier appeared at the conduction band of the Mg2Si/Si heterojunction interface. When the doping concentrations of Si and Mg2Si layer were 1017, and 1016 cm−3, respectively, the Mg2Si/Si heterojunction PD could obtain optimal photoelectric properties. Under these conditions, the maximum EQE was 70.68% at 800 nm, the maximum responsivity was 0.51 A/W at 1000 nm, the minimum NEP was 7.07 × 10−11 WHz–1/2 at 1000 nm, the maximum detectivity was 1.4 × 1010 Jones at 1000 nm, and the maximum on/off ratio was 141.45 at 1000 nm. The simulation and optimization result also showed that the Mg2Si/Si heterojunction PD could be used for visible and SWIR photodetection in the wavelength range from 400 to 1500 nm. The results also provide technical support for the future preparation of eco-friendly heterojunction photodetectors.

Technology CAD (TCAD) Simulations of Mg2Si/Si Heterojunction Photodetector Based on the Thickness Effect.

Research on infrared detectors has been widely reported in the literature. For infrared detectors, PbS, InGaAs, PbSe, InSb, and HgxCd1-xTe materials are the most widely used and have been explored for photodetection applications. However, these are toxic and harmful substances which are not conducive to the sustainable development of infrared detectors and are not eco-friendly. Mg2Si is a green, healthy, and sustainable semiconductor material that has the potential to replace these toxic and damaging photoelectric materials, making photoelectric detectors (PDs) green, healthy, and sustainable. In this work, we report on the results of our simulation studies on the PN junction Mg2Si/Si heterojunction PD. A model structure of Mg2Si/Si heterojunction PD has been built. The effects of Mg2Si and Si layer thickness on the optical and electrical performance of Mg2Si/Si heterojunction PD are discussed. For the purpose of this analysis, we consider electrical performance parameters such as I–V curve, external quantum efficiency (EQE), responsivity, noise equivalent power (NEP), detectivity, on-off ratio, response time, and recovery time. The simulation results show that the Mg2Si/Si heterojunction PD shows optimum performance when the thickness of Si and Mg2Si layers are 300 nm and 280 nm, respectively. For the optimized structure, the reverse breakdown voltage was found to be −23.61 V, the forward conduction voltage was 0.51 V, the dark current was 5.58 × 10−13 A, and the EQE was 88.98%. The responsivity was found to be 0.437 A/W, the NEP was 6.38 × 10−12 WHz1/2, and the detectivity was 1.567 × 1011 Jones. With the on-off ratio of 1566, the response time was found to be 0.76 ns and the recovery time was 5.75 ns. The EQE and responsivity peak wavelength of PD show a redshift as the thickness of Mg2Si increases. The Mg2Si heterojunction PD can effectively detect infrared light in the wavelength range of 400 to 1400 nm. The simulation results can be utilized to drive the development of green Mg2Si/Si heterojunction PD in the future.

Fine structural and photoluminescence properties of Mg2Si nanosheet bundles rooted on Si substrates

Creating vertically aligned 2D nanostructures is a promising approach to achieving advanced electronic and optoelectronic materials. In this study, Mg2Si nanosheet bundles were synthesized by Ca atom extraction from CaSi2 microwalls grown on Si substrates via thermal annealing in a MgCl2/Mg mixed vapor. The nanosheet bundle structure was modified to compound nanosheet bundles from previously reported Si nanosheet bundles. The observed Mg2Si nanosheets consist of thin Mg2Si layers, and well-defined fine-scale Mg2Si superlattice-like structures were achieved in the nanosheet bundles. In addition, the Raman scattering and photoluminescence properties were examined, and structural and electronic modifications of the nanosheet bundle compared with the bulk crystals were suggested. To obtain tailored properties and functionalities of the nanosheet bundles, structural modification of layered crystals is a useful technique.

Effect of insert materials on microstructure and mechanical properties of Al/Mg bimetal produced by a novel solid-liquid compound process

A novel lost foam casting solid-liquid compound method was developed for the preparation of the A356 aluminum alloy/AZ91D magnesium alloy bimetal (Al/Mg bimetal), and the effect of insert materials on microstructure and mechanical properties of the Al/Mg bimetal was studied in this paper. Obtained results indicated that the insert materials played a great role in the bonding of the Al/Mg bimetal. The Al/Mg bimetal with a defect-free and uniform metallurgical interface was achieved by use of the A356 aluminum alloy solid insert. With an optimized parameter in the condition of the AZ91D magnesium alloy solid insert, the Al/Mg bimetal also obtained a metallurgical bonding. Nevertheless, the crack defects were always found in the interfaces of the bimetallic samples produced with the AZ91D solid insert. The formation mechanism of the crack were proposed by stress distribution, thermodynamics and intermetallic compounds (IMCs) analyses. The microstructures exhibited that the interfaces of the bimetallic samples prepared with different insert materials were constituted by Al3Mg2+Mg2Si layer, Al12Mg17+Mg2Si layer as well as Al12Mg17+δ-Mg eutectic layer. The Al/Mg bimetal produced with the A356 solid insert possessed a much higher bonding strength compared to the bimetal obtained with the AZ91D solid insert, whereas their hardnesses were basically same. The fractured samples produced with different insert materials showed brittle fracture morphologies, and the fractures primarily occurred between the Al3Mg2+Mg2Si layer and Al12Mg17+δ-Mg eutectic layer.

Growth Kinetics of Magnesium Silicide Formation Via Reaction of Mg Gas and Si Substrates

The thermal, electrical, optical, and chemical properties of magnesium silicide (Mg2Si) have led to consideration of this semiconducting material for use in thermoelectric, optical, sensor, corrosion mitigation, and other applications. The relative non-toxicity and earth-abundant nature of the constituent elements of this silicide are also attractive characteristics. One approach for generating patterned magnesium silicide structures for use in devices is the direct conformal reaction of patterned silicon structures with magnesium gas. The kinetic mechanism controlling such conformal gas/solid reaction will be discussed in this presentation. The rate of thickening of magnesium silicide films, via the reaction of magnesium gas with planar silicon single crystal substrates, has been examined via measurements of mass change (∆m/A) and film thickness (∆X from SEM analyses of reacted cross-sections) as a function of time at 600oC. To avoid oxidation during such reaction, experiments were conducted within metal ampoules that had been carefully sealed in an argon atmosphere. Upon heating of the sealed ampoules to 600oC within an argon atmosphere tube furnace, magnesium gas (generated from solid magnesium within the ampoule) migrated to, and underwent reaction with, the planar silicon substrate. Measurements of ∆m/A vs. time and ∆X vs. time were both consistent with a parabolic rate law for the thickening of the Mg2Si layer, with the rate constants from both types of measurements in good agreement. Variations in the magnesium gas diffusion distance, and in the orientation of the starting silicon single crystal, were found to have negligible influence on the reaction kinetics. Such kinetic data were consistent with Mg2Si formation controlled by solid-state diffusion through the Mg2Si product layer. Inert marker experiments (using MgO particles) were used to determine the dominant interface at which new Mg2Si formed, and to evaluate the associated diffusing species controlling such formation. Kinetic analyses from this solid/gas reaction study will be compared to prior work on the formation of Mg2Si via solid-state reaction of magnesium with silicon. Figure 1

Inhibiting Brittle Intermetallic Layer in Magnesium/Aluminum Bimetallic Castings via In Situ Formation of Mg2Si Phase

A quasi-continuous Mg2Si layer is formed in situ at the magnesium/aluminum interface of bimetallic castings, by selecting a Si-containing aluminum alloy and overcasting process control. This effectively inhibits the formation of brittle intermetallic compounds (Al3Mg2, Al12Mg17) during the casting process, and the mechanisms are discussed based on phase diagram calculations and experimental validation. It is, thus, recommended to select Si-containing Al alloys as substrate for Mg/Al bimetallic castings.

Characteristics and Formation Mechanism of the Interface of Mg/Al Bimetallic Composites Prepared by Lost Foam Casting

In the present work, the Mg/Al bimetallic composites were successfully prepared by the lost foam casting (LFC) process, and the characteristics and formation mechanism of the interface of the Mg/Al bimetallic composites were investigated. The results show that a uniform and compact metallurgical interface with an average thickness of about 1400 μm was formed between magnesium alloy and aluminum alloy. The interface layer of the Mg/Al bimetallic composites was composed of three different reaction layers, namely the Al12Mg17+δ(Mg) eutectic layer adjacent to the magnesium matrix, the Al12Mg17+Mg2Si interlayer and the Al3Mg2+Mg2Si layer close to the aluminum matrix. The microhardnesses of the interface layer were remarkably higher than those of the magnesium and aluminum matrixes. The stress strength of the Mg/Al bimetallic composites was up to 47.67 MPa. The fractograph of the push out sample mainly showed a brittle fracture nature. The formation of the interface of the Mg/Al bimetallic composites was attributed to the fusion and diffusion bonding. With the variations of the concentrations of the different elements at the interface, the Al3Mg2 intermetallic phase first formed near to the aluminum matrix, and then the Al12Mg17 and Mg2Si successively generated toward the magnesium matrix, finally obtaining the interface layer of the Mg/Al bimetallic composites.

Defect-induced room-temperature visible light luminescence in Mg2Si:Al films

The Al-doped Mg2Si thin films were fabricated on sapphire substrates by magnetron sputtering technique, and the influences of different Al doping contents on the Raman scattering and room-temperature (RT) photoluminescence (PL) of Mg2Si thin films were investigated. The crystal structure, morphology, composition, Raman scattering and PL property of the thin film were examined using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy, respectively. XRD results indicate that the intensity of diffraction peaks of Al-doped Mg2Si thin films are higher than that of undoped Mg2Si thin film, and decrease with increasing Al doping content. The FESEM image shows a few cavities in the surface of the film. The EDS results show that the thin films have the Al content of 0, (1.17 ± 0.1) at.%, (1.53 ± 0.1) at.%, (1.86 ± 0.08) at.% and (2.76 ± 0.11) at.%, respectively. The results of Raman scattering measurement reveal that all samples have the characteristic peak of Mg2Si. And Al dopant-induced Raman peak centered at 441 cm−1 was detected. Room-temperature photoluminescence of the Mg2Si:Al film was observed for the first time. Two visible light luminescence peaks center about 580 nm (2.14 eV) and 630 nm (1.97 eV), respectively, which originate from the different energy levels transition at the interface between crystalline Mg2Si and MgO surface layer. With decreasing excitation power, the position of the maximum of PL has no obvious change and the intensity drops significantly.

Microstructural Characterization of AA6061 Versus AA6061 HIP Bonded Cladding–Cladding Interface

Microstructural characterization using scanning electron microscopy and scanning transmission electron microscopy (TEM/STEM) was carried out near the interface between the two AA6061 alloys that were hot isostatically pressed (HIP) to clad Zr laminated U-10 wt.% Mo metallic nuclear fuel. The HIP-bonded AA6061–AA6061 interface consisted of discontinuous layer of Mg2Si along with traces of fine MgO dispersoids and small precipitates of Al19(Fe, Cr, Cu)4MnSi2. To examine the presence of statistical variation, quantitative microscopy was also conducted, using several HIP’ed samples, to measure the relative linear density of the Mg2Si precipitates at the HIP bonded AA6061–AA6061 interface. In order to better understand the formation of discontinuous Mg2Si layer, solid-to-solid diffusion couple experiments were carried out using temperature and time relevant to HIP. The discontinuous Mg2Si layer was not observed in diffusion couples that were rapidly water-quenched, but those slowly cooled in air and in furnace developed the discontinuous Mg2Si. Presence of oxygen, confirmed by electron energy loss spectroscopy via STEM, at the interface would be the potential driving force for the migration of Mg and Si atoms, where Mg would preferentially react with oxygen to form MgO, and excess Mg would react with Si to form Mg2Si during cooling. Faster cooling after HIP may minimize the formation of excessive Mg2Si.

Study of the Very First Stages of Mg Growth onto Si(100)

Generation of ultra-thin oxide layers (in the nanometer range) is currently a technological lock for numerous applications such as microelectronics, spintronics or even molecular electronics. A precise study of the stages of growth of Mg is essential before studying the growth of the oxide. In this work we report and discuss an experimental study of the very first stages of Mg growth onto Si(100) by Scanning Tunneling Microscopy-Spectroscopy (STM-STS), Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). First, we have shown that an amorphous underlayer is formed onto the silicon substrate for Mg deposits of 0.25 monolayers (ML). This underlayer is attributed to a Mg2Si silicide formed at RT during Mg deposition. Then, using an original growth method based on alternate cycles of magnesium monolayer adsorption and room temperature (RT) oxidation, we did grow ultra-thin magnesium oxide films onto Si(100). Our study revealed that the ultra-thin Mg2Si layer at the MgO/Si(100) interface acts as a diffusion barrier and prevents oxidation of the highly-reactive silicon during magnesium oxide growth.

Fabrication and microstructure evolution of Al/Mg bimetal using a near-net forming process

ABSTRACTThe Al/Mg bimetal was fabricated by using the lost-foam casting method that is considered a near-net forming process, and the microstructure evolution of the Al/Mg bimetal from different cross-section locations of the bimetal was investigated in the present work. An obvious interface layer generated in the middle of the aluminum and magnesium, which showed a variation for different cross-section locations of the bimetal. The interface layer at the bottom cross-section location had a maximum thickness, wherein a big gap was observed. The thicknesses of the interface layer gradually decreased from the bottom location to the top location. At the middle cross-section location, the interface layer was uniform and compact. In contrast, the non-uniform interface layer was obtained at the top cross-section location, and the partial location had no the interface layer. The interface layers at the bottom and middle locations consisted of three reaction layers including the Al12Mg17 + δ-Mg, the Al12Mg17 + Mg2Si, and the Al3Mg2 + Mg2Si layers. However, the partial location at the top cross-section location only had the Al12Mg17 + δ-Mg layer.

Effects of Melt-to-Solid Insert Volume Ratio on the Microstructures and Mechanical Properties of Al/Mg Bimetallic Castings Produced by Lost Foam Casting

A356 aluminum and AZ91D magnesium alloys, which act as a solid insert and a melt, respectively, were used to prepare Al/Mg bimetallic castings using the lost-foam casting process, and the effects of the melt-to-solid volume ratio (VR) on the microstructures, mechanical properties, and fractographies of the Al/Mg bimetallic castings were investigated in this paper. Obtained results show that the average thickness of the reaction layer between aluminum and magnesium significantly increased with increasing VR, and a compact and uniform interface was obtained with a VR of 14.6. The reaction layers of all the bimetallic castings obtained by different VRs mainly consisted of the Al12Mg17 + δ eutectic layer close to the magnesium matrix, the Al12Mg17 + Mg2Si intermediate layer as well as the Al3Mg2 + Mg2Si layer next to the aluminum base. The microhardnesses of reaction layers of all the bimetallic castings with different VRs were considerably higher than those of the magnesium and aluminum matrix alloys, particularly the Al3Mg2 layer. Excessive thick reaction layer and pore defects remarkably weakened the bonding strength of the bimetallic castings, especially pore defects, and a relative maximum shear strength was obtained with a VR of 14.6. The fractographs of the push-out samples showed a change in the fracture surface from a mixed brittle and ductile fracture nature to that of a brittle fracture nature with the increase of VR.

Effect of Ca addition and heat treatment on the A390(S)/AM60(L) interface microstructure

Overcasting is a new kind of dissimilar joining technique used to produce the aluminum(solid)/magnesium(liquid) bonding bi-metallic material in this study. For the Al/Mg (A390/AM60) bi-metallic samples, the interface microstructures are the research points, which directly influence the mechanical properties. It is, therefore, of vital importance to find a method to improve the interface microstructures. This research focused on the effect of the calcium (Ca) addition in the liquid Mg alloys and the heat treatment on the A390/AM60 interface microstructures of the bi-metallic samples. The testing results showed that, with Ca addition in AM60, owing to two possible reasons, the interface microstructure and the shear strength of the A390/AM60 bi-metallic samples could be improved. The heat treatment could further improve the interface microstructure and the mechanical properties by dissolving β-Mg17Al12 into α-Mg and destroying the Mg2Si layer structure.

Growth, structure, optical and electrical properties of Si/2D Mg2Si/Si(111) double heterostructures and Schottky diodes on their base

AbstractMg2Si layers were grown on silicon by RDE at 150 °C and by SPE at 160 °C, and they were covered by silicon cap grown by MBE at 150‐180 °C. The silicide layers and the silicon cap were investigated by in situ and ex situ methods. The 2D Mg2Si layer continuity and electrical properties were conserved during cap growth. The point defects in the structure are dominated by contamination of the substrate and by diffusion of the not reacted Mg into silicon. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure, morphology and electrical properties of Mg2Si layers deposited by pack cementation

Magnesium silicide (Mg2Si) is a promising narrow gap semiconductor which can be used as a thermoelectric material. Chemical vapor deposition by pack cementation, which is a simple and low cost technique, was used for the first time in this work for the formation of Mg2Si compound. A series of experiments were carried out at temperatures 500–650°C with different deposition times ranging between 15 and 180min. As a result single phase thick layers have been prepared, depending on growth temperature and deposition time. Mg2Si was formed as a result of the Mg diffusion into the Si matrix while the film thickness increased with the deposition time, and temperature. Electrical and optical properties of the grown layers have been investigated. The examination of the as formed material was completed by performing thermal stability tests, for the determination of the safe service temperature range of the coupons. From all the experimental outcomes, it is concluded the optimum conditions for the formation of Mg2Si films is at 650°C for a 180min deposition period.

Reactive wetting in liquid magnesium/silica and magnesium/silicon systems

The reactive wetting of SiO2 and Si by molten Mg in a flowing Ar atmosphere was studied using an improved sessile drop method. The initial contact angles in the Mg/SiO2 system decreased from 56° to 35° as temperature increased from 973K to 1073K, and they decreased very rapidly with time during isothermal holding. The interfacial reaction led to the formation of a distinct reaction zone, consisting mainly of a thin Mg2Si layer, an MgO layer, a periodic alternatively arranged MgO and Mg2Si layer, and an aggregated Mg2Si–MgO mixture layer. The formation mechanism of these complex structures was discussed based on thermodynamic and kinetic considerations. Moreover, the effect of the interfacial reaction on the wetting improvement was examined and the primary contribution was ascribed to the formation of Mg2Si at the interface, which was further demonstrated by the result in the Mg/Si system.

Influence of Si(111) √3×√3 - R30 ° -Sb surface phase on the formation and conductance of low-dimensional magnesium silicide layer on Si(111) substrate

Using electron energy loss spectroscopy, Raman spectroscopy, and conductance measurements in the temperature range 20–500 K we have investigated doping of two-dimensional Mg silicide using the Sb surface phase. The doping process was performed in two steps including formation of the Sb surface phase followed by reactive deposition of Mg. It was shown that additional levels appear in the Mg2Si band gap resulting in increasing conductance at high temperatures. The Sb doped Mg2Si layer has a band gap of about 1.2 eV.