Transport studies of $$\hbox {CeO}_{2}$$ molecular device and adsorption behavior of CO on $$\hbox {CeO}_{2}$$ device: a first-principles investigation

Using density functional theory and the non-equilibrium Green’s function formalism, the transport and CO adsorption properties of \(\hbox {CeO}_{2}\) molecular device are studied. The band structure shows that \(\hbox {CeO}_{2}\) nanostructure exhibits semiconducting nature. The electron density is found to be more in oxygen sites rather than in cerium sites along \(\hbox {CeO}_{2}\) nanostructure. The density of states spectrum shows the variation in density of charge upon adsorption of CO on CeO\(_2\) device. The transmission spectrum provides the insights on the transition of charge in \(\hbox {CeO}_{2}\) molecular device upon adsorption of CO along the scattering region. I–V characteristics confirm the adsorption of CO with the variation of current along \(\hbox {CeO}_{2}\) molecular device. The findings show that \(\hbox {CeO}_{2}\) two probe molecular device can be efficiently used for CO detection in the atmosphere.     

Dual-material double-gate tunnel FET: gate threshold voltage modeling and extraction

A new analytical model for the gate threshold voltage (\(V_\mathrm{TG}\)) of a dual-material double-gate (DMDG) tunnel field-effect transistor (TFET) is reported. The model is derived by solving the quasi-two-dimensional Poisson’s equation in the lightly doped Si film and employing the physical definition of \(V_\mathrm{TG}\). A numerical simulation study of the transfer characteristics and \(V_\mathrm{TG}\) of a DMDG TFET has been carried out to verify the proposed analytical model. In the numerical calculations, extraction of \(V_\mathrm{TG}\) is performed based on the transconductance change method as already used for conventional metal–oxide–semiconductor FETs (MOSFETs). The effects of gate length scaling, Si film thickness scaling, and modification of the gate dielectric on \(V_\mathrm{TG}\) are reported. The dependence of \(V_\mathrm{TG}\) on the applied drain bias is investigated using the proposed model. The proposed model can predict the effect of variation of all these parameters with reasonable accuracy.     

Analog and RF performance of doping-less tunnel FETs with $$\hbox {Si}_{0.55} \hbox {Ge}_{0.45}$$ source

This paper reports studies of a doping-less tunnel field-effect transistor (TFET) with a \(\hbox {Si}_{0.55} \hbox {Ge}_{0.45}\) source structure aimed at improving the performance of charge-plasma-based doping-less TFETs. The proposed device achieves an improved ON-state current (\(I_{{\mathrm{ON}}} \sim {4.88} \times {10}^{-5}\,{\mathrm{A}}/\upmu {\mathrm{m}}\)), an \(I_\mathrm{ON}/I_\mathrm{OFF}\) ratio of \({6.91} \times {10}^{12}\), an average subthreshold slope (\(\hbox {AV-SS}\)) of \(\sim \) \({64.79}\,{\mathrm{mV/dec}}\), and a point subthreshold slope (SS) of 14.95 mV/dec. This paper compares the analog and radio of frequency (RF) parameters of this device with those of a conventional doping-less TFET (DLTFET), including the transconductance (\(g_{{\mathrm{m}}}\)), transconductance-to-drain-current ratio \((g_\mathrm{m}/I_\mathrm{D})\), output conductance \((g_\mathrm{d})\), intrinsic gain (\(A_{{\mathrm{V}}}\)), early voltage (\(V_{{\mathrm{EA}}}\)), total gate capacitance (\( C_{{\mathrm{gg}}}\)), and unity-gain frequency (\(f_{{\mathrm{T}}}\)). Based on the simulated results, the \(\hbox {Si}_{0.55}\hbox {Ge}_{0.45}\)-source DLTFET is found to offer superior analog as well as RF performance.     

Spin filtering in a $$\updelta $$-magnetic-barrier nanostructure modulated by Rashba and Dresselhaus spin–orbit couplings

We theoretically investigated the electron-spin transport properties of an antiparallel double \(\updelta \)-magnetic-barrier nanostructure modulated by spin–orbit coupling (SOC), which could be fabricated experimentally by depositing two ferromagnetic stripes with horizontal magnetization on the top and bottom of an InAs/Al\(_{x}\)In\(_{1-x}\)As semiconductor heterostructure. Both Rashba and Dresselhaus SOCs were taken into account, and the transmission coefficient, conductance, and spin polarization calculated analytically by means of the improved transfer matrix method. The electron-spin transport through this nanosystem is found to be strongly dependent on the SOC. The electron-spin polarization is also found to vary with the strength of the SOC, potentially enabling tunable spin filters for use in spintronic applications.     

Investigation of trigate JLT with dual-<Emphasis Type="Italic">k</Emphasis> sidewall spacers for enhanced analog/RF FOMs

This paper shows the potential benefits of using the trigate junctionless transistor (JLT) with dual-k sidewall spacers to enhance analog/radio-frequency (RF) performance at 20-nm gate length. Simulation study shows that the source-side-only dual-k spacer (dual-kS) JLT can improve all analog/RF figures of merit (FOMs) compared with the conventional JLT structure. The dual-kS JLT shows improvement in intrinsic voltage gain (\(A_{V0}\)) by \(\sim \)44.58 %, unity-gain cutoff frequency (\(f_\mathrm{T}\)) by \(\sim \)7.67 %, and maximum oscillation frequency (\(f_\mathrm{MAX}\)) by \(\sim \)6.4 % at drain current \((I_\mathrm{ds}) = 10\,\upmu \hbox {A}/\upmu \hbox {m}\) compared with the conventional JLT structure. To justify the improvement in all analog/RF FOMs, it is also found that the dual-kS structure shows high electron velocity near the source region because of the presence of an additional electric field peak near the source region, resulting in increased electron transport efficiency and hence improved transconductance (\(g_\mathrm{m}\)). Furthermore, the dual-kS JLT shows a reduction in the electric field value near the drain end, thereby improving short-channel effects.     

Electronic properties of graphyne nanotubes filled with small fullerenes: a density functional theory study

The encapsulation of small fullerenes into graphyne nanotubes was studied to investigate the possibility of band gap engineering in these nanotubes. The electronic properties of zigzag (4,0) and (5,0) graphyne nanotubes filled with small \(\hbox {C}_{20}\) and \(\hbox {C}_{30}\) fullerenes were studied using density functional theory. It was found that the zigzag (4,0) and (5,0) graphyne nanotubes were semiconductors. These graphyne nanotubes filled with \(\hbox {C}_{20}\) and \(\hbox {C}_{30}\) fullerenes were shown p-type and n-type semiconducting properties, respectively. The energy band gap was dependent on the number of the encapsulated fullerenes. Our results demonstrated the ability of band gap engineering through the encapsulation of small fullerenes into graphyne nanotubes.     

Optimal design of the multiple-apertures-GaN-based vertical HEMTs with $$\hbox {SiO}_{2}$$ current blocking layer

Gallium nitride (GaN) based vertical high electron mobility transistor (HEMT) is very crucial for high power applications. Combination of advantageous material properties of GaN for high speed applications and novel vertical structure makes this device very beneficial for high power application. To improve the device performance especially in high drain bias condition, a novel GaN based vertical HEMT with silicon dioxide \((\hbox {SiO}_{2})\) current blocking layer (CBL) was reported recently. In this paper, effects of the thickness of CBL layer and the aperture length on the electrical and breakdown characteristics of GaN vertical HEMTs with \(\hbox {SiO}_{2}\) CBL are simulated by using two-dimensional quantum-mechanically corrected device simulation. Intensive numerical study on the device enables us to optimize and conclude that devices with \(0.5\hbox {-}\upmu \hbox {m}\)-thick \(\hbox {SiO}_{2}\) layer and \(1\hbox {-}\upmu \hbox {m}\)-long aperture will be beneficial considerations to improve the device performance. Notably, using the multiple apertures can effectively reduce the on-state conducting resistance of the device. On increasing the number of apertures, the drain current is increased but the breakdown voltage is decreased. Therefore, device with four apertures is taken as an optimized result. The maximum drain current of 84 mA at \(\hbox {V}_\mathrm{G}= 1\,\hbox {V}\) and \(\hbox {V}_\mathrm{D}= 30\,\hbox {V}\), and the breakdown voltage of 480 V have been achieved for the optimized device.     

20-nm T-gate composite channel enhancement-mode metamorphic HEMT on GaAs substrates for future THz applications

In this paper, the RF and DC behaviours of a SiN-passivated 20-nm gate length metamorphic high electron mobility transistor (MHEMT) on GaAs substrate with \({\updelta }\)-doped sheets on either side of the composite channel are studied using the Synopsys TCAD tool. The 20-nm enhancement-mode MHEMT with \({\updelta }\)-doped sheets on either side of the \(\hbox {In}_{0.75}\hbox {Ga}_{0.25}\hbox {As}\)/InAs/ \(\hbox {In}_{0.75}\hbox {Ga}_{0.25}\hbox {As}\) multilayer channel shows a transconductance of 3000 mS/mm, cut-off frequency (\({f}_{\mathrm{T}}\)) of 760 GHz and a maximum-oscillation frequency (\({f}_{\mathrm{max}}\)) of 1270 GHz. The threshold voltage of the device is found to be 0.07 V. The room-temperature Hall mobilities of the two-dimensional sheet charge density (2DEG) are measured to be over \(12800\,\hbox {cm}^{2}\)/Vs with a sheet charge density larger than 4 \(\times \) \(10^{12}\,\hbox {cm}^{-2}\). These high-performance enhancement-mode MHEMTs are attractive candidates for future terahertz applications such as high-resolution radars for space research and also for low-noise wide-bandwidth amplifier for future communication systems.     

Systematic study of elastic,electronic, and magnetic properties of lanthanum cobaltite oxide

The electronic structure, elastic constants, and magnetic properties of lanthanum cobaltite oxide \(\hbox {La}_{4}\hbox {Co}_{3}\hbox {O}_{9}\) compound, which crystallizes in orthorhombic space group Pnma, are investigated theoretically for the first time using the full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory plus Hubbard correction term (DFT \(+\) U). The calculated equilibrium lattice constants and fractional atomic coordinates are in a good agreement with available experimental data. Our result for the formation energy and elastic constants confirms that the predicted \(\hbox {La}_{4}\hbox {Co}_{3}\hbox {O}_{9}\) is mechanically stable. This compound is found to be ductile in nature in accordance with Pugh’s criteria. The anisotropy factors (\({A}_{1})\), (\({A}_{2})\), and (\({A}_{3})\) of \(\hbox {La}_{4}\hbox {Co}_{3}\hbox {O}_{9}\) material are also predicted through the elastic constants. The electronic band structures show metallic behavior; the conductivity is mostly governed by Co-3d and O-2p states. The total magnetic moments of the tetrahedral (\(\hbox {CoO}_{4})\) and octahedral (\(\hbox {CoO}_{6})\) environments are, respectively, 2.502 \(\mu _{B}\) and 2.874 \(\mu _{B}\), which are consistent with the experimental measurements.     

Structural,electrical and optical properties of $$\hbox {InGaZnO}_{4}$$ and $$\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}$$In29Sn3O48: a first-principles study

First-principles calculations were performed to investigate the electrical and optical properties of \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) with Sn-doped \(\hbox {In}_{2}\hbox {O}_{3}\) and \(\hbox {InGaZnO}_{4}\) (IGZO). The band structure, density of states, optical properties including dielectric function, loss function, reflectivity and absorption coefficient are calculated. The calculated total energy shows that the most stable crystal structures are type III for \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and type II for \(\hbox {InGaZnO}_{4}\). The band structure indicates the both \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and \(\hbox {InGaZnO}_{4}\) are direct gap semiconductors. The intrinsic band gap of \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) is much narrower than that of \(\hbox {InGaZnO}_{4}\), and results in a better electrical conductivity for \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\). The density of states shows the main hybridization occurring between In-4d and O-2p states for \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) while between In-4d In-5p, Zn-4s and O-2p states for \(\hbox {InGaZnO}_{4}\) near the valence band maximum. The reflectivity index \(R({\omega })\) shows that the peak value of \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and \(\hbox {InGaZnO}_{4}\) appears only in the ultraviolet range, indicating that these two materials have all excellent transparency. In addition, the absorption coefficient \({\alpha }({\omega })\) of both \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and \(\hbox {InGaZnO}_{4}\) is high in the ultraviolet frequency range, and therefore they show, a high UV absorption rate.     

First-principles investigation on transport properties of $$\hbox {Zn}_{2}\hbox {SnO}_{4}$$ molecular device and response toward $$\hbox {NO}_{2}$$NO2 gas molecules

The transport properties of a \(\hbox {Zn}_{2}\hbox {SnO}_{4}\) device along with adsorption properties of \(\hbox {NO}_{2}\) gas molecules on \(\hbox {Zn}_{2}\hbox {SnO}_{4}\) (ZTO) molecular devices are investigated with density functional theory using the non-equilibrium Green’s function technique. The transmission spectrum and device density of states spectrum confirm the changes in HOMO–LUMO energy level due to transfer of electrons between the ZTO-based material and the \(\hbox {NO}_{2}\) molecules. I–V characteristics demonstrate the variation in the current upon adsorption of \(\hbox {NO}_{2}\) gas molecules on the ZTO device. The findings of the present study clearly suggest that ZTO molecular devices can be used to detect \(\hbox {NO}_{2}\) gas molecules in the trace level.     

Ambipolar leakage suppression in electron–hole bilayer TFET: investigation and analysis

In this paper, we propose and simulate two new structures of electron–hole bilayer tunnel field-effect transistors (EHBTFET). The proposed devices are n-heterogate with \(\hbox {M}_{1}\) as overlap gate, \(\hbox {M}_{2}\) as underlap gate and employs a high-k dielectric pocket in the drain underlap. Proposed structure 1 employs symmetric underlaps (Lgs = Lgd = Lu). The leakage analysis of this structure shows that the lateral ambipolar leakage between channel and drain is reduced by approximately three orders, the OFF-state leakage is reduced by one order, and the \(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\) ratio is increased by more than one order at \(V_\mathrm{{GS}}=V_{\mathrm{DS}} =1.0\) V as compared to the conventional Si EHBTFET. The performance is improved further by employing asymmetric underlaps (\(\hbox {Lgs}\ne \hbox {Lgd}\)) with double dielectric pockets at source and drain, called as proposed structure 2. The pocket dimensions have been optimized, and an average subthreshold swing of 17.7 mV/dec (25.5% improved) over five decades of current is achieved with an ON current of \(0.23~\upmu \hbox {A}/\upmu \hbox {m}\) (11% improved) in proposed structure 2 in comparison with the conventional EHBTFET. Further, the parasitic leakage paths between overlap/underlap interfaces are blocked and the OFF-state leakage is reduced by more than two orders. A high \(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\,\hbox {ratio}~>10^{9}\) (two orders higher) is achieved at \(V_{\mathrm{DS}} =V_{\mathrm{GS}} =1.0~\hbox {V}\) in the proposed structure 2 in comparison with the conventional one.     

A novel process variation immune dopingless zero sub-threshold slope and zero impact ionization FET (DL-Z$$^{}$$FET) based on transition metals

Transition metal (TM) electrodes based dopingless zero sub-threshold slope and zero impact ionization FET (DL-Z\(^{2}\)FET) is reported in this paper. The work-function engineering of TM electrodes is used for charge plasma based electrostatic pseudo doping. Work-function difference between TM electrodes and the undoped silicon film induces p\(^{+}\) and n\(^{+}\) regions in the film. TMs exhibit easy tunability of work-function and their CMOS fabrication compatibility pledges for their potential applications as these electrodes. A technology computer-aided design simulation study is performed to provide physical insight into its working mechanism and performance. It exhibits all the inherent characteristics of conventional Z\(^{2}\)FET, viz. zero slope switching, high \(I_{ON}/I_{OFF}\) ratio, lower operating voltages, immunity towards hot electron degradation and gate controlled hysteresis. The detrimental doping control issues, mobility degradation due to heavy doping and statistical random dopant fluctuations can no more obviate the device performance, it results in more process variations immune design. Hence it can be a potential fast switching transistor.     

Numerical analysis of transmission coefficient,LDOS, and DOS in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ resonant tunneling MODFETs

Numerical analysis of the transmission coefficient, local density of states, and density of states in superlattice nanostructures of cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) resonant tunneling modulation-doped field-effect transistors (MODFETs) using \(\hbox {next}{} \mathbf{nano}^{3}\) software and the contact block reduction method is presented. This method is a variant of non-equilibrium Green’s function formalism, which has been integrated into the \(\hbox {next}\mathbf{nano}^{3}\) software package. Using this formalism in order to model any quantum devices and estimate their charge profiles by computing transmission coefficient, local density of states (LDOS) and density of states (DOS). This formalism can also be used to describe the quantum transport limit in ballistic devices very efficiently. In particular, we investigated the influences of the aluminum mole fraction and the thickness and width of the cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N}\) on the transmission coefficient. The results of this work show that, for narrow width of 5 nm and low Al mole fraction of \(x = 20\,\%\) of barrier layers, cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) superlattice nanostructures with very high density of states of 407 \(\hbox {eV}^{-1}\) at the resonance energy are preferred to achieve the maximum transmission coefficient. We also calculated the local density of states of superlattice nanostructures of cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) to resolve the apparent contradiction between the structure and manufacturability of new-generation resonant tunneling MODFET devices for terahertz and high-power applications.     

A simulation study of voltage-assisted low-energy switching of a perpendicular anisotropy ferromagnet on a topological insulator

We present a novel memory device that consists of a thin ferromagnetic layer of Fe deposited on topological insulator thin film, \(\hbox {Bi}_{2}\hbox {Se}_{3}\). The ferromagnetic layer has perpendicular anisotropy, due to MgO deposited on its top surface. When current is passed on the surface of \(\hbox {Bi}_{2}\hbox {Se}_{3}\), the surface of the \(\hbox {Bi}_{2} \hbox {Se}_{3}\) becomes spin polarized and strong exchange interaction occurs between the d electrons in the ferromagnet and the electrons conducting the current on the surface of the \(\hbox {Bi}_{2}\hbox {Se}_{3}\). Part of the current is also shunted through the ferromagnet, which generates spin transfer torque in the ferromagnet. The exchange interaction torque along with voltage-controlled magnetic anisotropy allows ultralow-energy switching of the ferromagnet. We perform micromagnetic simulations and predict switching time of the order of 2.5 ns and switching energy of the order of 0.88fJ for a ferromagnetic bit with thermal stability of \(43\,k_\mathrm{{B}}T\). Such ultralow-energy and high-speed switching of a perpendicular anisotropy ferromagnet on a topological insulator could be utilized for energy-efficient memory design.     

Simulation-based performance analysis of an ultra-low specific on-resistance trench SOI LDMOS with a floating vertical field plate

An ultra-low specific on-resistance \((R_\mathrm{{on,sp}})\) trench SOI LDMOS with a floating vertical field plate structure (FVFPT SOI) is proposed in this paper. A floating vertical plate (FVFP) is introduced into the filled oxide trench of a conventional trench SOI LDMOS (CT SOI) to improve its electrical performance. We conduct related performance analysis to this device by simulation and investigate the effects of different parameters on its performance. The FVFP causes an assisted depletion effect especially for the trench surface regions. An ultra-low \(R_\mathrm{{on,sp}}\) is therefore obtained in the FVFP device due to higher drift region doping concentration \((N_\mathrm{{d}})\). A breakdown voltage (BV) of 188V and a \(R_\mathrm{{on,sp}}\) of \(0.9 \hbox { m}\Omega \, \hbox { cm}^{2}\) are realized on a 4.8-\({\upmu }\hbox {m}\)-long drift region, a 7.5-\({\upmu }\hbox {m}\)-thick top-silicon layer and a 0.5-\({\upmu }\hbox {m}\)-thick buried oxide (BOX) layer by our simulation. Eventually, the \(R_\mathrm{{on,sp}}\) for the FVFPT SOI can be reduced by more than 60%, while its BV is maintained the same class as the CT SOI, and the figure of merit (FOM) is enhanced by 155%. And a set of optimal parameters, including the structure parameters of plate and the property parameters of device, are obtained.     

Asymmetric dual-k spacer trigate FinFET for enhanced analog/RF performance

In this paper, we aim to explore the potential benefits of using source side only dual-k spacer (Dual-kS) trigate FinFET structure to improve the analog/RF figure of merit (FOM) for low power operation at 20 nm gate length. It has been observed from the results that Dual-kS (inner spacer high-k) FinFET structure improves the coupling of the gate fringe field to the underlap region towards the source side and results into improvement in transconductance \((g_{m})\) and output conductance \((g_{ds})\). It was also found that drain side only dual-k spacer (Dual-kD) improves the coupling of the gate fringe field to the underlap region towards the drain side which helps to shift away the drain field from gate edge and results into improvement in output conductance \((g_{ds})\) only at the cost of increase in Miller capacitance. A comparative simulation study has been performed on four different device structures namely both side low-k spacers (conventional), both side dual-k spacer (Dual-kB), Dual-kD and Dual-kS structures. From the simulation study, it was found that that Dual-kS structure has potential to improve \(g_{m}\) by \(\sim \)8.7 %, \(g_{ds}\) by \(\sim \)32.24 %, intrinsic gain \((A_{V0})\) by \(\sim \)11.44 %, early voltage \((V_{EA})\) by \(\sim \)47.59 %, maximum oscillation frequency (\(f_{MAX}\)) by \(\sim \)1.7 % and the ratio of gate-source capacitance and gate-drain capacitance \((C_{gs}/C_{gd})\) by \(\sim \)15.27 % with a slight reduction in the value of unity gain cut-off frequency (\(f_{T}\)) by \(\sim \)0.58 % in comparison to the conventional structure at drain current \((I_{ds})\) of \(10\,\upmu \)A/\(\upmu \)m. Furthermore, to reduce the drain field influence on the channel region, we also studied the effect of asymmetric drain extension length on Dual-kS FinFET structure.     

Theoretical investigation of electronic performance,half-metallicity,and magnetic properties of Cr-substituted BaTe

We have investigated the structural, electronic, and ferromagnetic properties of chromium (Cr)-doped rocksalt BaTe (\(\hbox {Ba}_{1-x}\hbox {Cr}_{x}\hbox {Te}\)) compounds with compositions \(x = 0.25\), 0.5, and 0.75, based on density functional theory with generalized gradient approximation of Wu–Cohen (GGA-WC) and Tran–Blaha-modified Becke–Johnson (TB-mBJ) potential using the WIEN2k package. We found that the electronic structure showed half-metallic ferromagnetic character with spin polarization of 100 % around the Fermi level. In addition, the minority-spin bands depicted a half-metallic ferromagnetic (HMF) gap and half-metallic (HM) gap. The improved HMF and HM gaps found with the TB-mBJ potential are higher than with the GGA-WC approximation. These large HM gaps make \(\hbox {Ba}_{1-x} \hbox {Cr}_{x}\hbox {Te}\) compounds promising candidates for use in spintronics applications.     

Thermoelectric,electronic and structural properties of CuNMn3 cubic antiperovskite

Using first-principles calculations, in this work we report the structural, electronic and, for the first time, thermoelectric properties of CuNMn3 cubic antiperovskite. The structural properties are explored using GGA and \(\hbox {GGA}{+}\hbox {U}\) approximations. Structural optimization shows that the compound is stable in the ferrimagnetic phase, and the electronic properties confirm the metallicity of this compound. At room temperature, high values of the Seebeck coefficient are obtained between \(-\) 0.8 and 0.5 \(\upmu (\hbox {eV})\) chemical potential, whereas outside this region the Seebeck coefficient diminishes. Also, thermal conductivities are minimal in this region of chemical potential; therefore, the material can be used to achieve thermocouples. Thermal conductivity is high for 900 K. The maximum electrical conductivity is obtained at 0.38 \(\upmu (\hbox {eV})\) chemical potential, with a value of \(4.15\times 10^{20}(\Omega ~\hbox {ms})^{-1}\). The figure of merit ZT values obtained are still low, so for thermoelectric applications of the material, it is necessary to improve the figure of merit coefficient by doping the material with a suitable element.     

Investigation on the structural,elastic, electronic,and magnetic properties of half-metallic $$\hbox {Co}_{2}\hbox {MnSi}$$ and CoMnIrSi via first-principles calculations

We investigated the structural, elastic, electronic, and magnetic properties of \(\hbox {Co}_{2}\hbox {MnSi}\) and CoMnIrSi full-Heusler compounds by means of density functional theory based on the full-potential linearized augmented plane wave (FP-LAPW) approach. The generalized gradient approximation as proposed by Wu and Cohen (GGA-WC) was employed to treat the exchange-correlation effect. The results show that both alloys are structurally and mechanically stable. \(\hbox {Co}_{2}\hbox {MnSi}\) is almost elastically isotropic, while CoMnIrSi is anisotropic, and both alloys are ductile. The studied compounds have perfect spin polarization of 100 %, with down-spin bandgap of 0.796 eV and 0.728 eV, respectively. The calculated magnetic properties indicate that the Slater–Pauling rule is satisfied in both cases. Finally, the effect of strain on the half-metallic properties of \(\hbox {Co}_{2}\hbox {MnSi}\) and CoMnIrSi was also investigated by varying the lattice constant over a wide range.