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abstract: Abstract The transport properties and optical transmittance and absorption spectra for the nostoichiometric amorphous indium gallium zinc oxide (a IGZO) films with gallium and zinc deficiencies are investigated. The resistivity and carrier concentration variation with temperature both reveal that the films possess degenerate semiconductor (or metal) characteristics. The thermopower is negative and decreases linearly with decreasing temperature, indicating the electron diffusion thermopower governs the thermal transport process in each film. Using free electron like model, we extracted the electron effective mass, which is about three times as large as that of the stoichiometric one and increases with increasing carrier (electron) concentration. Neglecting the variation in the energy with the wavevector near the valence band maximum and using the free electron like model, we also obtained the electron effective mass via the optical absorption spectra measurement. The magnitude of the effective mass obtained via optical spectra measurement is comparable to that obtained via thermopower measurement for each film. Our results strongly suggest that the nostoichiometric a IGZO films possess free electron like pseudo energy bandstructure.
author_names: Xin Zhu

Yang Yang

X D Liu

Zhi-Qing Li
title: Electron effective mass and electronic structure in nonstoichiometric amorphous Indium Gallium Zinc Oxide films
year: 2020

abstract: The transport properties and optical transmittance and absorption spectra for the nostoichiometric amorphous Indium Gallium Zinc Oxide (a IGZO) films with Gallium and Zinc deficiencies are investigated. The resistivity and carrier concentration variation with temperature both reveal that the films possess degenerate semiconductor (or metal) characteristics. The thermopower is negative and decreases linearly with decreasing temperature, indicating the electron diffusion thermopower governs the thermal transport process in each film. Using free electron like model, we extracted the electron effective mass, which is about three times as large as that of the stoichiometric one and increases with increasing carrier (electron) concentration. Neglecting the variation in the energy with the wavevector near the valence band maximum and using the free electron like model, we also obtained the electron effective mass via the optical absorption spectra measurement. The magnitude of the effective mass obtained via optical spectra measurement is comparable to that obtained via thermopower measurement for each film. Our results strongly suggest that the nostoichiometric a IGZO films possess free electron like pseudo energy bandstructure.
author_names: Xin Zhu

Yang Yang

Xin-Dian Liu

Zhi-Qing Li
title: Electron effective mass and electronic structure in nonstoichiometric a IGZO films.
year: 2018

abstract: The electronic structure, density of states (DOS) effective mass are calculated for tetragonal TlInSe2 from first principle in the framework of density functional theory (DFT) The electronic structure of TlInSe2 has been investigated by Quantum Wise within GGA. The calculated band structure by Hartwigsen Goedecker Hutter (HGH) pseudopotentials (psp) shows both the valence band maximum and conduction band minimum located at the T point of the Brillouin zone. Valence band maximum at the T point and the surrounding parts originate mainly from 6s states of univalent Tl ions. Bottom of the conduction band is due to the contribution of 6p states of Tl and 5s states of In atoms. Calculated DOS effective mass for holes and electrons are mDOS h* 0.830m e, mDOS h* 0.492m e, respectively. Electron effective masses are fairly isotropic, while the hole effective masses show strong anisotropy. The calculated electronic structure, density of states and DOS effective masses of TlInSe2 are in good agreement with existing theoretical and experimental results.
author_names: Narmin A Ismayilova

Guseyn Orudzhev

Sakin H Jabarov
title: First principle calculation of the electronic structure, DOS and effective mass TlInSe2
year: 2017

abstract: The crystal and electronic structure of semiconductor nanowire systems have shown sensitive response to mechanical strain, enabling novel and improved electrical, and optoelectrical properties in nanowires by strain engineering. Here, the response of current voltage (I V) characteristics and band structure of individual p doped GaAs nanowires to bending deformation is studied by in situ electron microscopy combined with theoretical simulations. The I V characteristics of the nanowire change from linear to nonlinear as bending deformation is applied. The nonlinearity increases with strain. As opposed to the case of uniaxial strain in GaAs, the bending deformation does not give rise to a change in the band gap of GaAs nanowire according to in situ electron energy loss spectroscopy (EELS) measurements. Instead, the response to bending deformation can be explained by strain induced valence band shift, which results in an energy barrier for charge carrier transport along the nanowire. Moreover, the electron effective mass decreases as the strain changes from compressive to tensile across the GaAs nanowire in the bent region. Results from this study shed light on the complex interplay between lattice strain, band structure, and charge transport in semiconductor nanomaterials.
author_names: Lunjie Zeng

Thomas Kanne

Jesper Nygard

Peter Krogstrup

Wolfgang Jager

Eva Olsson
title: The Effect of Bending Deformation on Charge Transport and Electron Effective Mass of p doped GaAs Nanowires
venue: physica status solidi (RRL) Rapid Research Letters
year: 2019

abstract: The effective mass is a convenient descriptor of the electronic band structure used to characterize the density of states and electron transport based on a free electron model. While effective mass is an excellent first order descriptor in real systems, the exact value can have several definitions, each of which describe a different aspect of electron transport. Here we use Boltzmann transport calculations applied to ab initio band structures to extract a density of states effective mass from the Seebeck Coefficient and an inertial mass from the electrical conductivity to characterize the band structure irrespective of the exact scattering mechanism. We identify a Fermi Surface Complexity Factor: {N}_{\rm{v}\ast {K}\ast $Nv*K* from the ratio of these two masses, which in simple cases depends on the number of Fermi surface pockets {N}_{\rm{v}\ast (Nv* and their anisotropy K* both of which are beneficial to high thermoelectric performance as exemplified by the high values found in PbTe. The Fermi Surface Complexity factor can be used in high throughput search of promising thermoelectric materials.Electronic materials: In search of the right massA simple method for determining a material's thermoelectric properties is developed by researchers in the United States and Belgium. Jeffrey Snyder from Northwestern University and his co workers' model could simplify the search for materials that efficiently generate electricity from waste heat. Even though the environment of an electron in a solid is very complex, the way an electron moves through a solid's lattice of atoms can be treated as if it is moving in free space. However, because of the influence of its environment an effective mass, not its true mass, is used to model the movement of electrons and that material's properties. But this effective mass can be defined in several ways depending on which material property is being modeled. Snyder et al. determine that the ratio of two different effective masses, as computed from different electronic properties, could be a good method to identify novel thermoelectric materials and can be associated with the "complexity" of the electronic structure.
author_names: Zachary M Gibbs

Francesco Ricci

Guodong Li

Hong Zhu

Kristin Aslaug Persson

Gerbrand Ceder

Geoffroy Hautier

Anubhav Jain

Gerald Jeffrey Snyder
title: Effective mass and Fermi surface complexity factor from ab initio band structure calculations
venue: npj Computational Materials
year: 2017

abstract: Abstract The first principles hybrid density functional theory is applied to the contrastive investigation on the structural and electronic properties of wurtzite ZnO under hydrostatic strain and uniaxial strain along c axial, and the effect of strain on electron effective mass. It is observed that the structural transformation of the wurtzite ZnO occurs under tensile hydrostatic strain and compressive uniaxial strain. The transformation of ZnO from wurtzite phase to graphitelike phase is accompanied by the transition from a direct to indirect band gap. The deformation potentials that quantify the changes of band gap with strain are also reported. When the hydrostatic strain changes from compression to tension, the electron effective masses at G point in S T and D directions, and average electron effective mass decrease linearly. For the uniaxial strain, the changes of electron effective mass are dissimilar to the hydrostatic results.
author_names: Yaqin Wang

Wu Tang

Junhao Zhu

Jie Liu
title: Strain induced change of band structure and electron effective mass in wurtzite ZnO: A first principles study
year: 2015

abstract: Abstract Density functional theory was used to calculate the electronic band structure, effective mass, and optical dispersion of 2 mercapto 5 methyl 1,3,4 thiadiazole (MMTD) The all electron, full potential, linearized augmented plane wave method was used. The exchange correlation potential was treated using the local density approximation, generalized gradient approximation, and modified Becke Johnson approximation. The calculated band structure shows that MMTD has a direct energy bandgap. The partial density of states revealed strong hybridization between N p, C p, N s, and H s orbitals. The electronic charge density distribution confirmed partial ionic and strong covalent C N, C C, C H, and N N bonds. We also calculated the optical dielectric function and related optical properties (refractive index, extinction coefficient, absorption coefficient, and reflectivity)
author_names: Sikander Azam

Ali H Reshak
title: Electronic structure, effective mass, and optical dispersion of 2 mercapto 5 methyl 1,3,4 thiadiazole: density functional theory calculations
year: 2014

abstract: In this paper, we studied the electronic properties, effective masses, and carrier mobility of monolayer \hbox {MoS}_2$$MoS2 using density functional theory calculations. The carrier mobility was considered by means of ab initio calculations using the Boltzmann transport equation coupled with deformation potential theory. The effects of mechanical biaxial strain on the electronic properties, effective mass, and carrier mobility of monolayer \hbox {MoS}_2$$MoS2 were also investigated. It is demonstrated that the electronic properties, such as band structure and density of state, of monolayer \hbox {MoS}_2$$MoS2 are very sensitive to biaxial strain, leading to a direct indirect transition in semiconductor monolayer \hbox {MoS}_2$$MoS2. Moreover, we found that the carrier mobility and effective mass can be enhanced significantly by biaxial strain and by lowering temperature. The electron mobility increases over 12 times with a biaxial strain of 10% while the carrier mobility gradually decreases with increasing temperature. These results are very useful for the future nanotechnology, and they make monolayer \hbox {MoS}_2$$MoS2 a promising candidate for application in nanoelectronic and optoelectronic devices.
author_names: Huynh V Phuc

Nguyen Ngoc Hieu

Bui D Hoi

Nguyen Van Hieu

Tran Viet Thu

Nguyen Man Hung

Victor V Ilyasov

Nikolai A Poklonski

Chuong Van Nguyen
title: Tuning the Electronic Properties, Effective Mass and Carrier Mobility of MoS2 Monolayer by Strain Engineering: First Principle Calculations
venue: Journal of Electronic Materials
year: 2017

abstract: The band engineering using strain and electric field of monolayer silicon phosphide (2D SiP) has been investigated by first principle calculation. The biaxial strain is used to tune the electronic band gap from 1.91 to 0.7 eV by applying compressive strain 0 10% and 1.91 1.0 eV by tensile strain from 0 to 12% Furthermore, SiP shows metallic behaviour beyond 12% of compressive strain and 14% of tensile strain. However, the negligible effect of the external electric field on the electronic band structure of 2D SiP shows the sustainability of the monolayer. The stress vs strain curve shows the excellent mechanical stability of the monolayer SiP. 2D SiP also shows low electron effective mass for higher carrier mobility. Further, optical properties of the monolayer show the UV region absorption. Our results provide insights to possible mechanical tuning of SiP monolayer by applying external strain for nano electronic and nano optoelectronic device application.
author_names: Shivam Kansara

Prabal Dev Bhuyan

Yogesh Sonvane

Sanjeev K Gupta
title: Two dimensional silicon phosphide: low effective mass and direct band gap for future devices applications
venue: Journal of Materials Science
year: 2019

abstract: In this letter, we analyze a conceptual design for the operation of an Otto cycle heat machine driven by adiabatic modifications on the electronic effective mass. Such tailoring of it can be implemented, for instance, via the application of external electron fields in some materials, as in Gallium Nitride (GaN) We show that due both the energy quantization on this structure and the adiabatic transformation of the effective mass, the machine performance can be improved. The realization of classically inconceivable Otto machines, with an incompressible working substance, can be realized as well. Our finds hold in cases where the electronic effective mass, in the low temperature regime, remains constant during the isochoric strokes.
author_names: Cleverson Filgueiras
title: Quantum heat machines enabled by the electronic effective mass
year: 2019