| Advancements in material technology normally depend on the discovery of new materials with unique and desirable properties for the intended use thus inspires the technological transformations which shape the life of humanity.The two-dimensional layered materials?2DLMs?are atomically thin nano-sheets of van der Waal solids that can be exfoliated from the bulk due to weak nature of binding energies.Nanotechnology and nanoengineering techniques enable rapid advances in developing new materials for optoelectronic,nanoelectronic and thermoelectric devices.With modern semiconductor technology is becoming more sophisticated and controlling properties becomes more advance and complex.Searching the most optimal and promising materials with desirable parameters still show some underlying challenges.This underlying challenge is investigated by applying predictive first Principles calculations approach to guide research and get into insights of semiconductor materials for optoelectronic,nanoelectronic and thermoelectric applications.In this work,involves firs-principles investigation of two-dimensional ?-InSe and few-layer Tellurene for optoelectronic and nanoelectronic applications,while monolayer ?-Tellurene for thermoelectric applications.Their electronic and optical properties were investigated by use of density functional theory methods,while the thermoelectric properties of monolayer ?-Tellurene were calculated by employing the first-principles method combined with Boltzmann transport approach and by means of first deformation potential theoryIn addition,all means of steering the study of 2D materials properties is an effective strategies of obtaining properties of material with tailored characteristics suitable for optoelectronic and nanoelectronic device applications.In this work,it is performed to pursue of understanding properties of 2D materials i.e InSe and Tellurene.Many of the outcomes indicate that these 2D materials give promising properties for the next-generation nanoelectronics and optoelectronics devices.Nevertheless,still this researched area motivates unceasingly deep exploration of InSe and Tellurene crystals' properties and correlates strong motivation for further studies in this research area.We demonstrate remarkable properties of ?-InSe.We establish that quantum confinement played a big role in the manifestation of properties exhibited by monolayer and few-layer ?-InSe.Owing to the manifestation of quantum confinement;the band structures show direct to indirect transitions from bulk ?-InSe to few-layer ?-InSe.Similar to the work functions,the quantum effects manifest where the work function reduces sequentially from 5.22 eV?1 L?to 5.0 eV?6 L?,and then stagnated at 4.99 eV for 7 L and 8L and decrease to 4.77 eV in bulk ?-InSe.For optical properties,the imaginary function showed strong dependence on the thickness variation.The optical response can be efficiently tuned by varying the number of layers as seen in a shift of energy from high(monolayer?3.3 eV?to low?bulk ?-InSe?3.0 eV?,in?36?^C polarization?,which have appeared as exciting technique to tune the optical response of ?-InSe.The results implies that layer control provides an effective strategy to enhance layer-dependent properties in ?-InSe,and therefore offers a great potential for applications in the next-generation high-performance electronic and optoelectronic devices,and re-engineering of Schottky barrier.To Tellurene,it was established to be an emerging two-dimensional chiral semiconductor,with fascinating optical and electronic properties.We explored the electronic structure,and optical properties of few-layer Tellurene.The density functional theory?DFT?and many-body perturbation theory?MBPT?demonstrate that 2 L exhibited the indirect band structure,and the,3L,4 L,5 L and 6 L,all exhibit robust slightly indirect band structures,and due to structural reconstruction,which change to direct band structure at monolayer limit.2D-Tellurene exhibited tunable band gap from 1.0 eV for the monolayer to 0.3 eV for the six layer structure.The decreases of the band gap with increasing number of layer exhibit odd-even due quantum confinement size effect and disappearance of inversion symmetry in odd-numbered layer structures resulting in the anisotropic SOC splitting of the energy bands.Both optical spectra in?36?^C and?36?||C both directions show variation in optical gap values,which change the threshold of photo-absorption energy.Moreover,the results obtained shows that,electronic and optical properties in Te are layer dependent,and sufficient for fabrication of electronic and optoelectronic nanodevices,and this is essential in the realization of its full potentials.With the recent development in fabrication of Tellurene where there was successful experimental growth of two-dimensional?2D?Tellurene?Yixin et al.Nat.Electron,2018,1,228-236?and the recent study of unusually low thermal conductivity in atomically thin 2D tellurium?Jie Ren et al.Nanoscale,2018,10,12997?,motivated this part of this work.We carried out systematic calculations for the monolayer ?-Tellurene,focused on its,electrical transport electronic,and thermoelectric transport by means of density functional theory?DFT?combined with deformation potential theory and Boltzmann transport theory.We demonstrated that monolayer ?-Tellurene is dynamically and thermally stable up to 700 K,and has a band gap of 1.5 eV,and The mobilities are highly direction-temperature-dependent,with high room-temperature value of1343 cm2 V-1 s-1 and relaxation time of 283 fs in the armchair direction for hole transport.It is coincidently favorable in the armchair direction for both the Seebeck coefficient and the electrical conductivity,making the p-type monolayer Tellurene as a highly promising thermoelectric material.With cited lattice thermal conductivity,the maximum figure of merit?ZT?is 2.9 and 0.84 along the armchair and zigzag direction for p-type doping at 700 K,respectively.The predicted properties demonstrate that monolayer ?-Tellurene can be a prospective material towards thermoelectric applications. |
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