Gap Alloys Research Articles

Modeling and Sensitivity Estimation of a Dual Cavity Source Pocket-Based Charge Plasma Tunneling FET for Label-Free Biological Molecule Detection

A dual-source cavity charge plasma tunneling FET (DSC-SP-CPTFET) with SiGe Pocket is proposed, and its effectiveness as a biological sensor for label-free detection is explored. The fabrication complexity and cost have been reduced by using the charge-plasma concept. For improved sensing, an etched nanocavity is added to the upper and lower of the source metal section. The high-k (HfO2) gate oxide and minimal energy gap (Si0.6Ge0.4) alloy with a 40% mole fraction improve the current sensitivity by enhancing the drain current gradient. The sensitivity of the suggested biological sensor is assessed here for several neutral biological molecules, such as Gelatin, Keratin, Biotin, and 3-Aminopropyl-Triethoxysilane (APTES). Deoxyribonucleic acid (DNA), a charged biological molecule, is also considered with varying positive and negative charge densities. The suggested biological sensor shows a (SIDS)max of 2.21 × 1010 and a Sratio of 3.11 × 109 for biological molecules with higher dielectric constant at room temperature. Different electrostatic performances are estimated in the ON state, including energy band, electron (e-) BTBT rate, electrical field, and IDS-VGS characteristics. In addition, the proposed biological sensor provides a much superior drain current sensitivity (SIDS), current ratio sensitivity (Sratio), and average SS sensitivity (SSS) performance in the presence of both charged and neutral biological molecules.

Conceptual design and numerical analysis of a miscibility gap alloy-based solid-state thermal battery for electric vehicles

Heating the passenger cabin of electric vehicles at low temperatures consumes a large amount of battery power, resulting in a significant reduction in cruising range. On-board thermal energy storage is an effective way to improve the cruising range of electric vehicles in winter. Miscibility gap alloy is a new type of shape-stabilized composite phase change material, which has the advantages of high energy storage density, high thermal conductivity, low cost, and good safety. Therefore, using it to heat electric vehicles can increase their cruising range, prolong battery life, and reduce cost. In this paper, the concept of a compact on-board solid-state thermal battery based on miscibility gap alloy is proposed for the first time, and the heat charging, thermal insulation and heat discharging performance of the design are analysed based on numerical simulations. The results show that the thermal battery can reach a heat storage density of 553.8 Wh/L, and the average heat discharging power can reach 1.326 kW. The results of this paper can provide guidance for the engineering development of miscibility gap alloy-based solid-state thermal batteries.

Role of microstructure in the exploitation of self-healing potential in form-stable composite phase change materials based on immiscible alloys

Metallic Phase Change Materials (PCMs), based on solid-liquid transitions, represents one of the most promising technologies for efficient Thermal Energy Storage (TES), due to their superior thermal conductivity and energy storability per unit volume, but suffer of limited solutions for their handling at the molten state. The use of Miscibility Gap Alloys (MGAs) allows to manage PCM volume expansion and keep it confined when molten, preventing interaction with the environment. A relevant example is provided by the Al-Sn system, where Al covers the role of the high-temperature stable and highly thermal-conductive passive matrix and Sn the active PCM. The alloy can thus be considered a Composite PCM (C-PCM). The response fastness of these systems depends on their thermal diffusivity, subjected to abrupt variations under the presence of discontinuities and damages. In this sense, the authors investigated the possibility to employ molten Sn mobility in a potentially damaged C-PCM for self-healing purposes, aimed to restore, at least partially, the material continuity and thus its thermal diffusivity. Exudation heat treatments above the melting temperature of Sn were performed on sets of Al-40%wt. Sn metallic composites, produced either with powder metallurgy or liquid metal routes, in order to quantify and assess the mobility of the Sn under simulated operating conditions. Exudation tests assess Simple Mixed powders and liquid metal routes sample as the ones with the highest healing potential. Al dissolution and re-deposition was established by EDS analyses as one of the principal Sn mobility mechanisms. Laser Flash Analysis tests, as well as microstructural investigations, were performed on the samples before and after both healing-focused and simulated service heat treatments to evaluate the changes of thermal diffusivity. Healing-focused treatment at 250°C for 1 hour generally displayed a moderate thermal diffusivity recovery and simulated service by shorter cycles between 170°C and 270°C slightly reduce it. The beneficial role of healing focused heat treatments at 250°C for 1 hour suggests that the presence of fully molten Sn phase during service for relatively long time could be beneficial for functional healing. The requirements of suitable Al-Sn microstructures for self-healing purposes, granting at the same time the C-PCM functionalities, i.e., thermal energy storage and form-stability, were set.

Critical assessment of thermal conductivity models for Miscibility Gap Alloy-based composite Phase Change Materials for high temperature Thermal Energy Storage

Miscibility Gap Alloys (MGAs), such as Al-Sn-based systems, provide a viable solution for the development of composite Phase Change Materials (PCMs) for Thermal Energy Storage (TES) purposes. Their successful production depends on the cooling rate imposed to the melt. Finite Element Analyses (FEA), which relies also on thermal conductivity values, represent a powerful tool for the design of the production process. Thermal conductivity, which depends on the arrangement of the phases in the system, also affects the thermal response of the alloy. In the view of evaluating the impact of the phase morphology, the authors adapted some of the models developed for composites and solutions to Al-Sn and Al-Sn-Si-Mg alloys, characterized by broad solidification ranges in terms of composition and temperature and by significantly different phases thermal conductivity. In the fully-liquid range, Filippov and Novoselova model was selected for the description of both alloys. Models that consider sphere-like dispersions give values quite close to the theoretical upper Wiener bound when the high-melting phase is solid. The phase morphology impact is relevant when the solidification range is considered. The resulting arrangement-related thermal conductivity curves are compared to those supplied by CALPHAD-based software and to available literature data.

Use of Low Melting Point Metals and Alloys (Tm < 420 °C) as Phase Change Materials: A Review

Phase Change Materials (PCMs) are materials that release or absorb sufficient latent heat at a constant temperature or a relatively narrow temperature range during their solid/liquid transformation to be used for heating or cooling purposes. Although the use of PCMs has increased significantly in recent years, their major applications are limited to Latent Heat Storage (LHS) applications, especially in solar energy systems and buildings. PCMs can be classified according to their composition, working temperature and application. Metallic PCMs appear to be the best alternative to salts and organic materials due to their high conductivity, high latent heat storage capacity and wide-ranging phase change temperature, i.e., melting temperature and chemical compatibility with their containers. This paper reviews the latest achievements in the field of low-melting point metallic PCMs (LMPM-PCMs), i.e., those with melting temperatures of less than 420 °C, based on Zn, Ga, Bi, In and Sn. Pure LMPM-PCMs, alloy LMPM-PCMs and Miscibility Gap Alloy (MGA) LMPM-PCMs are considered. Criteria for the selection of PCMs and their containers are evaluated. The physical properties and chemical stability of metallic PCMs, as well as their applications, are listed, and new application potentials are presented or suggested. In particular, the novel application of metallic PCMs in casting design is demonstrated and suggested.

Effect of Process Parameters on Laser Powder Bed Fusion of Al-Sn Miscibility Gap Alloy

Al-Sn binary system is a miscibility gap alloy consisting of an Al-rich phase and a Sn-rich phase. This system is traditionally applied in bearings and more recently found application as form-stable phase change material (PCM) exploiting solid-liquid phase transition of Sn. A careful choice of production process is required to avoid macro-segregation of the two phases, which have different densities and melting temperatures. In the present study, the additive manufacturing process known as laser powder bed fusion (LPBF) was applied to an Al-Sn alloy with 20% volume of Sn, as a rapid solidification process. The effect of process parameters on microstructure and hardness was evaluated. Moreover, feasibility and stability with thermal cycles of a lattice structure of the same alloy were experimentally investigated. An Al-Sn lattice structure could be used as container for a lower melting organic PCM (e.g., a paraffin or a fatty acid), providing high thermal diffusivity thanks to the metallic network and a “safety system” reducing thermal diffusivity if the system temperature overcomes Sn melting temperature. Even if focused on Al-Sn to be applied in thermal management systems, the study offers a contribution in view of the optimization of manufacturing processes locally involving high solidification rates and reheat cycles in other miscibility gap alloys (e.g., Fe-Cu) with similar thermal or structural applications.

Al-Sn Miscibility Gap Alloy produced by Power Bed Laser Melting for application as Phase Change Material

Alloys based on the Al-Sn system are Miscibility Gap Alloys consisting of two phases: a low-melting Sn phase and a high-melting Al phase. The two phases are almost immiscible in solid state, with minimal miscibility of Al in liquid phase just above the Sn-phase melting temperature. This situation allows the alloy to be used as composite Phase Change Material, where the low-melting (active) phase (Sn) acts as the actual Phase Change Material, storing/releasing latent heat at each thermal cycle across its activation temperature, and the high-melting (passive) phase (Al) plays its main role in fast driving heat within the composite material, thanks to its high thermal conductivity. Thermal response of PCM composites is expected to be faster if the active phase is finely combined to the matrix. Moreover, if the active phase is embedded in the passive phase, leakage phenomena can be prevented and the continuity of the passive phase, acting as matrix, also allows residual structural properties to the composite above the temperature at which the low-melting phase is activated. In these conditions, the composite PCM can be considered as a form-stable composite material. In this paper, the effect of rapid solidification has been investigated as a tool to get suitable microstructure of an Al-Sn alloy in view of its application as a composite PCM. The rapid solidification has been obtained by a Power Bed Laser Melting (also known as Selective Laser Melting) process. In the case of positive results for microstructure, the process will allow to overcome critical points in the manufacturing of composite PCM parts by powder metallurgy, mainly consisting in limitations on size and geometrical features of the parts. Data availabilityThe raw data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study. The processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Numerical and Experimental Evaluation of Thermal Conductivity: An Application to Al-Sn Alloys

Evaluation of thermal conductivity of composite materials is extremely important to control material performance and stability in thermal applications as well as to study transport phenomena. In this paper, numerical simulation of effective thermal conductivity of Al-Sn miscibility gap alloys is validated with experimental results. Lattice Monte-Carlo (LMC) method is applied to two-phase and three-phase materials, allowing to estimate effective thermal conductivity from micrographs and individual phase properties. Numerical results are compared with literature data for cast Al-Sn alloys for the two-phase model and with a specifically produced powder metallurgy Al-10vol%Sn, tested using laser flash analysis, for a three-phase simulation. A good agreement between numerical and experimental data was observed. Moreover, LMC simulations confirmed the effect of phase morphology as well as actual phase composition on thermal conductivity of composite materials.

Effect of Different Production Processes on Metallic Composite Phase Change Materials for Thermal Energy Storage

Phase Change Materials (PCMs) can be applied in Thermal Energy Storage and Thermal Management systems, exploiting the storage and release of latent heat associated to a phase transition. Among them, metallic PCMs can be used at medium and high temperatures (i.e. above 150°C), storing higher heat per unit volume at higher temperatures with respect to the most widely investigated polymeric and salt-based PCMs. Miscibility Gap Alloys (MGAs) can be used to obtain multiple-phase mixtures in which the active phase (the actual PCM) is mixed to a second, high-melting temperature phase, with negligible interaction between them. These can actually be considered as fully metallic composite materials specifically developed for thermal management. Suitable microstructures can prevent leakage of active phase when the solid-liquid transition occurs, resulting in a form-stable PCM (FS-PCM). However, obtaining these microstructures it is not trivial. The present study focuses on a solid-liquid FS-PCM consisting of a ‘classical’ fully metallic FS-PCM, an Al-Sn based MGAs produced by powder metallurgy. The goal was to evaluate the effect of different production processes on thermal and mechanical behaviour of the PCM. Particularly, powder metallurgy routes including both simple mixing and ball milling were compared and further combined. Moreover, several compression and sintering conditions were considered, also substituting Al powders with Al-alloy powders, in order to optimize the material microstructures in view of suitable thermal and mechanical properties. Finally, the casting route with a rapid solidification approach was investigated for the same alloy.

Fabrication of Al-Bi frozen emulsion alloys due to high-intense ultrasound irradiation

The aim of this study is to develop an ultrasound-assisted process for fabrication of frozen emulsion alloys, which are a type of miscibility gap alloys (MGAs). Al-Bi system was used to produce 2-kg ingots of Al-Bi frozen emulsion alloys in the following two steps: (1) emulsification treatment of Al-Bi melt by introducing high-intense ultrasound vibrations into it in a temperature range of Al-Bi binodal decomposition, and (2) casting of the melt into a book mold. The ingot samples were analyzed with SEM/EDX for the alloy microstructure and bismuth particle distribution. Besides, cold model experiments, thermodynamic and CFD numerical simulations were performed to elucidate the underlying mechanisms of emulsification including droplet fragmentation and acoustic streaming.The results reveal that the alloys with Bi concentration of 4%~9.4% can be fabricated by the proposed technique. Within this range, 90% of Bi particles have a diameter under 10 µm, and the majority of them are incorporated into aluminum grains. Especially, a uniform microstructure is obtained when concentration of Bi is less than 6%. Emulsification was found to occur at the interface between two liquids when cavitation bubbles collapse in the interface vicinity followed by high-velocity micro-jetting which is responsible for the emulsion droplet formation. Another positive effect of ultrasound is acoustic streaming which is responsible for the effective agitation of molten bath preventing the sedimentation of Bi droplets during the ultrasound treatment and casting operation.

Combined powder metallurgy routes to improve thermal and mechanical response of Al−Sn composite phase change materials

Abstract Powder metallurgy processes are suitable to produce form-stable solid−liquid phase change materials from miscibility gap alloys. They allow to obtain a composite metallic material with good dispersion of low-melting active phase particles in a high-melting passive matrix, preventing leakage of the particles during phase transition and, therefore, increasing the stability of thermal response. Also, the matrix provides structural properties. The aim of this work is to combine conventional powder mixing techniques (simple mixing and ball milling) to improve active phase isolation and mechanical properties of an Al−Sn alloy. As matter of fact, ball milling of Sn powder allows to reduce hardness difference with Al powder; moreover, ball milling of the two powders together results in fine microstructure with improved mechanical properties. In addition, different routes applied showed that thermal response depends on the microstructure and, in particular, on the particle size of the active phase. In more detail, coarse active phase particles provide a fast heat release with small undercooling, while small particles solidify more slowly in a wide range of temperature. On the other hand, melting and, consequently, heat storage are independent of the particle size of the active phase. This potentially allows to “tailor” the thermal response by producing alloys with suitable microstructure.

Miscibility gap alloys with a ceramic matrix for thermal energy storage

New miscibility gap alloys with a ceramic matrix have been explored in the ZrO2–Al, AlN–Al, AlN-(Al–Si), Al2O3–Al and MgO–Al systems with a view to creating oxidation-resistant macroscopically solid, phase change-enhanced, thermal energy storage materials. Materials were manufactured by mixing the components, pressing and firing at 700 °C under argon. Oxidation tests at 700 °C in air for up to 72 h showed a mix of responses. Despite favourable thermodynamic properties of some published Ellingham diagrams, samples in the ZrO2–Al system underwent a strong exchange reaction, which did not result in a useful material. In the AlN–Al, AlN–(Al–Si) systems, viable MGA-type materials with encapsulated Al particles providing latent heat storage within a solid matrix were formed. There was no degradation of the materials after 24 h of oxidation testing; however, severe oxidation of the Al or Al–Si was observed after 72 h. The Al2O3–Al and MgO–Al systems not only formed a viable ceramic matrix material after firing, but also showed no signs of Al oxidation after 72 h in air at 700 °C. These results open up a promising new series of thermal energy storage materials, some of which appear to have very good oxidation resistance under the test conditions.

Ball-milled Al–Sn alloy as composite Phase Change Material

The present study concerns a fully metallic solid-liquid composite Phase Change Material based on an Al–Sn Miscibility Gap Alloy produced by powder metallurgy, including its ball-milling, compression and further sintering heat treatment. The materials obtained by different routes display a narrow melting temperature range at about 230 °C, corresponding to the phase transformation of Sn- or of Sn-rich eutectic. The microstructures obtained by this manufacturing process lead to form-stable PCMs, which can keep their shape and prevent active phase leakage in service conditions. Ball milling of metal powders as mixing technique allowed to obtain a very fine microstructure, resulting in stability of thermal response and improvement of mechanical properties. Among the investigated Al–40Sn mass% samples, the most promising were those compressed at 240 °C followed by sintering at 500 °C.

The morphology regulation and plasmonic spectral properties of Au@AuAg yolk-shell nanorods with controlled interior gap.

Au@AuAg yolk-shell nanorods with tunable and uniform interior gap were synthesized through galvanic replacement reaction, where Au@Ag core-shell nanorods served as sacrificial templates and HAuCl4 solution served as reductant. The effects of HAuCl4, Ag shell thickness and aspect ratio (AR) of Au nanorods on the morphology of Au@AuAg yolk-shell nanorods had been investigated systemically. The results clearly indicated that AuAg alloy shell thickness of Au@AuAg yolk-shell nanorods could be increased from 3.6 to 10.0nm by varying the amount of HAuCl4. Meanwhile, the shape of AuAg alloy shell could be tuned by changing the shape of Ag coating. With the increasing of Ag coating thickness, the interior gap could be finely tuned in the range from 2.6 to 8.1nm. The uniformity of interior gap could be improved by increasing the AR of Au nanorods. All these tunable geometries can further affect the plasmonic spectral properties of Au@AuAg yolk-shell nanorods. Because of the appearance of interior gap, the longitudinal localized surface plasmon resonance (LSPR) peak of Au@AuAg yolk-shell nanorods was located between that of bare Au nanorods and Au@Ag core-shell nanorods without interior gap. The increase of outer AuAg shell thickness can weaken the coupling between the inner and outer surface of the AuAg shell and lead to the decrease of AR, so the transverse and longitudinal LSPR bands gather together. The decrease of Ag coating thickness can enhance the coupling between inner Au nanorod and outer AuAg shell, which results in the red shift of the longitudinal LSPR band. This paper provides a method for studying the plasmonic coupling between two metal surfaces with a metal layer or a dielectric layer, which is also a new approach for regulating the plasmonic spectral properties of bimetallic nanoparticles. The controllability of Au@AuAg yolk-shell nanorods in both the interior gap and outer alloy shells makes them have potential applications in biomedicine, catalysis, nanoreactors, and energy storage.

People & Appointments

Powder metallurgy processes are suitable to produce form-stable solid−liquid phase change materials from miscibility gap alloys. They allow to obtain a composite metallic material with good dispersion of low-melting active phase particles in a high-melting passive matrix, preventing leakage of the particles during phase transition and, therefore, increasing the stability of thermal response. Also, the matrix provides structural properties. The aim of this work is to combine conventional powder mixing techniques (simple mixing and ball milling) to improve active phase isolation and mechanical properties of an Al−Sn alloy. As matter of fact, ball milling of Sn powder allows to reduce hardness difference with Al powder; moreover, ball milling of the two powders together results in fine microstructure with improved mechanical properties. In addition, different routes applied showed that thermal response depends on the microstructure and, in particular, on the particle size of the active phase. In more detail, coarse active phase particles provide a fast heat release with small undercooling, while small particles solidify more slowly in a wide range of temperature. On the other hand, melting and, consequently, heat storage are independent of the particle size of the active phase. This potentially allows to “tailor” the thermal response by producing alloys with suitable microstructure.

A Review of Different Techniques for Improving the Performance of Amorphous Silicon based Solar Cells

Hydrogeneted amorphous silicon (a-Si:H) based solar cells are promising candidates for future developments in the photovoltaic industry. In fact, amorphous silicon technology offers significant advantages including low cost fabrication and possibility to deposition on flexible substrat as well as low temperature fabrication. Much progress has been made since the first single junction cell in amorphous silicon made in 1976 by Carlson and Wronski. However, the performance of the solar cells based on a-Si:H is limited by the high defect density and degradation induced by exposure to light, or Staebler-Wronski effect. To become competitive, the performance of the solar cells based on a-Si:H must be improved. In order to improve the performance of a-Si:H solar cells, much research is directed to optimization techniques. The improvement in performance is therefore based on the optimization of the different layers of the solar cell, in particular, the window layer and the absorber layer (intrinsic). The aim of this work is to give an overview on the different techniques and strategies that is used to improve the performance of solar cell. This work is therefore focus in three main areas: first, optimization of window layer, in particular, the p/i interface using wide band gap alloys such as a-SiC:H, second development of high quality absorber layer using band gap engineering, and alloys such as a-SiGe:H. last, optimizing n-type layer and i/n interface.

Density functional theory investigation of half-metallic ferromagnetism in V-doped GaP alloys

The spin polarized structural, electronic, and magnetic properties of zincblende Ga1−xVxP (x = 0, 0.25, 0.50, 0.75, and 1) alloys are studied by using the full-potential linearized augmented plane waves with local orbital (FP-L/APW + lo) method within the spin-polarized density functional theory (spin-DFT). The exchange and correlation (XC) energy is defined in all this approach by the generalized gradient approximation (GGA-PBE) of Perdew-Burke-Ernzerhof, whereas the GGA + U (U is the Hubbard term of the Coulomb repulsion correlation) functional is employed specially to treat and improve the electronic and magnetic properties of these compounds. The structural properties show the stability of Ga1−xVxP alloys in ferromagnetic phase, where their equilibrium structural parameters (lattice constant (a0), bulk modulus (B0), and its first-pressure derivative (B’) are evaluated. The elastic constants for the cubic system (C11, C12, and C44) and anisotropy are computed in the goal to prove the mechanical stability of these compounds. The electronic results reveal that both Ga0.25V0.75P and VP alloys have a perfect half-metallic nature, while the Ga0.75V0.25P alloy is a semiconductor. From band structures, we observe that the unfilled 3d-V orbitals increase the rise of spin-exchange splitting energy Δx(d) and Δx(pd); consequently, we found that the minority-spin case presents an attractive effective potential comparing to the majority-spin case. The total magnetic moment of Ga0.75V0.25P, Ga0.25V0.75P and VP alloys are found in integer value (2μB), affirming their complete half-metallic behavior. Moreover, we estimate the s-d exchange constant N0α (conduction band) and the p-d exchange constant N0β (valence band) to analyze contributions of conduction and valence bands in the exchange splitting process; in the other hand, the observed p-d hybridization reduces the atomic magnetic moment of V element from its free space charge value and produces weak local magnetic moments on the nonmagnetic sites of Ga and P atoms.

First-Principles Simulations of Stability, Optical and Electronic Properties of Competing Phases in Chalcopyrite-Based Photoelectrodes

Photoelectrochemical (PEC) hydrogen production is one promising approach to economically generating renewable fuels, yet the widescale deployment of leading photoelectrodes (e.g. GaInP-based devices) has been hampered by issues with durability, efficiency and cost. Chalcopyrite-based tandem photoelectrodes are attractive alternatives in that they offer a great flexibility in the choice of component materials necessary that drive the reactions for different device designs, offering ways to reduce the cost and to improve the performance. The synthesis of low-band gap chalcopyrites like CuInSe2 and alloys with CuGaSe2 (CIGSe) are known to exhibit a variety of Cu-poor phases (ordered-vacancy compounds or OVCs) that can greatly influence the resulting properties of fabricated devices, while the existence and properties of these phases in wider-band gap chalcopyrite compounds and alloys remains largely unexplored. Using hybrid functional calculations, we discuss the stability, optical and electrical properties of OVCs in a number of other chalcopyrite chemistries beyond CIGSe. We discuss the influence of such phases on the resulting absorption and band offsets that would result upon their formation, which have implications in device design. We additionally discuss experimental fingerprints that could be used to identify the existence of such phases in synthesized material. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the HydroGEN Consortium within the Department of Energy Office of Energy Efficiency & Renewable Energy (EERE) and Fuel Cell Technologies Office.

On-sun testing of Miscibility Gap Alloy thermal storage

The ability of a C-Zn Miscibility Gap Alloy (MGA) material to operate as a combined solar receiver and storage was investigated. MGA thermal energy storage materials comprise metallic PCM particles embedded within a conducting metal or semi-metal matrix to form a macroscopically solid combined latent heat/sensible heat storage material. A receiver containing 4 × 1L MGA storage modules was mounted on a solar concentrating dish. The storage material was directly illuminated by concentrated solar radiation at a flux of approximately 105 kW/m2, readily attaining surface temperatures of 520–530 °C, well above the phase change temperature of 420 °C. Single step charging led to a state of charge of 80% without exceeding a nominal surface temperature of 530 °C. Cycling on and off sun in the range 460–520 °C was used to achieve a state of 99% charged. Thermal performance of the MGA during solar charging and its discharge by natural cooling is presented and analysed.

Prediction of Large Enhancement of Electron Mobility in Direct Gap Ge1−xSnx Alloy

Group IV semiconductor‐based alloy Ge1−xSnx can be grown on Si platform and a crossover from indirect (L valleys) to direct gap (Γ valley) occurs for x > 0.08. The direct gap alloy shows promise for use in high‐speed electronic and photonic devices. An earlier study predicted that the electron mobility in the alloy would increase by a few orders of magnitude above the value for pure Ge. In that work, however, electrons were assumed to occupy only the low effective mass Γ valley and only the deformation potential acoustic phonon and alloy scatterings were considered. In the present work, we give a more realistic estimate of the values of electron mobility in direct gap GeSn alloy, considering the Γ and L valleys and the phonon (deformation potential acoustic, optical and intervalley), alloy, and impurity scatterings. The effect of strain, both tensile and compressive, on the mobility is also studied. It is found that for higher alloy composition and suitable strain, mobility values ∼2 × 105 cm−2/V · s, more than 50 times higher than the value in pure Ge (3900 cm2/V · s) may be achieved. This is attributed to increased separation between Γ and L valleys and consequent reduction in intervalley scattering.