Variation Of Electron Effective Mass Research Articles

Laser-induced modulation of optical band-gap parameters in the III–V-type semiconductors from the density-of-state (DOS) calculations

Optical band gap ( $$E_{\mathrm{g}0} $$ ) is a parameter of paramount importance in describing various transport and opto-electronic properties of the III–V-type low band-gap semiconductors. In the present communication, an attempt has been made to develop an energy–momentum ( $$E{-}{\bar{k}} $$ ) dispersion relation for studying the density-of-state (DOS) and band-gap-related parameters. The external laser excitation has been treated as a perturbation. It has been shown theoretically that due to such excitation with different intensity (I) and wavelength $$(\lambda )$$ , the band edge of the conduction band (CB) of the III–V compound semiconductors moves vertically upward, indicating laser modulation (increase) of $$E_{\mathrm {g}0} $$ and related parameters compared to those of the normal ones (unperturbed). Therefore, in the presence of light, the original CB edge forms a pseudo-CB edge above the unperturbed CB edge in the forbidden band (FB) zone. This new development of the ( $$E{-}{\bar{k}} $$ ) relationship has also been extended for the estimation of exact optical effective mass (OPEM) of an electron in some III–V compound semiconductors. The OPEM variation with carrier concentration showed a continuous decreasing nature, while the corresponding variation of electron effective mass (EEM) (without laser excitation) exhibited an increasing trend. The present theoretical results would be important for the deeper understanding of the variation of OPEM with I and $$\lambda $$ . The observed new results will also be beneficial for studying laser-induced effects in semiconductor heterostructures with different applications in optoelectronic devices.

Effects of Intercalation on the Electronic Properties of Multilayer Tmdc Materials

Over the past few years, Transition Metal Dichalgogenide (TMDC) materials have shown great potentials for next generation nanoelectronic applications. Both monolayers and van der Waals (vdW) heterostructures drawn from them have shown really interesting electronic and optoelectronic properties [1][2]. The electronic structure and properties of these materials can be significantly influenced by the number of material layers involved and van der Waals interaction between the layers of TMDC. Recent advancement in processing technology has allowed the controlled growth of vdW heterostructures by stacking and their successful integration in electronic device applications for low power electronics. Effects of intercalation of a 2D TMDC sheet in between two monolayers of MoS2 have been shown in recent literature [1]. In this work, we have provided a detailed simulation study of the effects of biaxial strain on electronic properties like bandgap and carrier effective mass in the conduction band of vdW intercalated trilayers (MoS2/MX2/MoS2 where, M=Mo/W and X=Se/S) from first principle simulation. We provide simulation results of three different stacking configurations: AAA, ABA and ACA as shown in fig. 1. The simulation was carried out using PWSCF package of Quantum Espresso [3] simulation tool. After geometry optimization and relaxation of different stacking configurations, self-consistent field (SCF) calculation was done to determine electronic configuration for the relaxed atomic structure followed by bandstructure calculation using the same package. We used normconserving pseudopotenial functions in our simulation framework and 24x24x1 Monkhorst-Pack k-point grids for sampling in the brillouin zone. After extracted of geometrically relaxed structure, biaxial strain was applied to the lattice and the effects on band structure and carrier effective mass were observed. The carrier effective mass at the brillouin zone symmetry points was calculated by simple parabolic fitting to the extracted ab-initio band structure. At first, we performed structural geometry optimization for ABA and ACA stacking configurations. We extracted the optimized values of lattice constant and interlayer separation. Our extracted results showed good agreement with the values reported in [1]. Fig 2. Shows the effect of variation of electron effective mass at K point in the brillouin zone for the simulated lattice structure under strain. The figure reveals lowering of effective mass at K points in the brillouin zone as we move from compressive to tensile strain regime. It is also seen that, for stacking configuration AAA in all three lattice structures, the simulation reveals a slightly lower carrier effective mass at K point for high compressive strain. However, as we move towards tensile strain regime, the stacking configurations reveal almost similar effective masses at K point. The gradual lowering of carrier effective mass at K point in the Brillouin zone is consistent with the results reported in literature[4]. Fig.3 shows the effect of strain on bandgap of different stacking configurations of multilayer TMDC materials as extracted from simulation. In all three material structures used in this study, we see a gradual lowering of bandgap with strain and therefore a gradual shift from semiconducting to metallic properties which is consistent with the results reported in [5] for bilayer TMDC heterostructures. Of the three structures used in this study, MoS2/WSe2/MoS2 shows the lowest bandgap and therefore the quickest transition to metallic state under tesile strain as seen from fig. 3(c). As observed from our simulation results, at unstrained condition, MoS2/WSe2/MoS2 trilayer showed a direct bandgap for all three stacking configurations. On the other hand, unstrained MoS2/MoSe2/MoS2 and MoS2/WS2/MoS2 trilayers showed indirect bandgap for all three stackings. The AAA stacking configuration is observed to be showing the lowest bandgap when compressive strain is being applied to the lattice. Some results extracted from our simulation for unstrained lattice configuration is listed below: LatticeStackingLattice Constant(A0) Bandgap, Eg(eV)Effective mass,mK(m0)AAA3.2390.7070.5035MoS2/MoSe2/MoS2 ABA3.240.7290.5129ACA3.2380.7520.5142AAA3.1861.2930.5753MoS2/WS2/MoS2 ABA3.1831.0740.5886ACA3.1861.1470.5877AAA3.2410.50350.5035MoS2/WSe2/MoS2 ABA3.2370.5420.5084ACA3.2430.5620.5097 In this work, we have provided a detailed simulation results on the effects of intercalation on electronic properties of TMDC materials. The findings of this study would be helpful in modeilng electronic devices using these material structures.

Effects of strain on the electron effective mass in GaN and AlN

Stress is known to strongly alter the effective mass in semiconductors, changing the mobility of carriers. Transport measurements on AlGaN/GaN heterostructures indicated a large increase in mobility under tensile strain [M. Azize and T. Palacios, J. Appl. Phys. 108, 023707 (2010)]. Using first-principles methods, we calculate the variation of electron effective mass in GaN and AlN under hydrostatic and biaxial stress. Unexpected trends are found, which are explained within k·p theory through a variation of the interband momentum matrix elements. The magnitude of the effective-mass reduction is too small to explain the experimentally reported increase in mobility.

Electron spin relaxation in GaAs1−xBix: Effects of spin-orbit tuning by Bi incorporation

The electron spin relaxation in n-type and intrinsic GaAs1−xBix with Bi composition 0≤x≤0.1 is investigated from the microscopic kinetic spin Bloch equation approach. The incorporation of Bi is shown to markedly decrease the spin relaxation time as a consequence of the modification of the spin-orbit interaction, which shows the feasibility of GaAs1−xBix in the applications of spintronic devices. We demonstrate that the density and temperature dependences of spin relaxation time in GaAs1−xBix resemble the ones in GaAs. Meanwhile, the Bir-Aronov-Pikus mechanism is found to be negligible compared to the D'yakonov-Perel' mechanism in intrinsic sample. Due to the absence of direct measurement of the electron effective mass in the whole compositional range under investigation, we further explore the effect of a possible variation of electron effective mass on the electron spin relaxation.

Tight-binding approach to calculation of localised perturbations in semiconductors

The replacement of As by N in GaAs introduces several pertubations, including both a change in potential at the N site and also long range strain relaxation in the crystal. It can be very useful to describe this perturbation in terms of the change in the Hamiltonian, ΔH, due to the introduction of N. Using plane-wave approaches, ΔH treats explicitly all atomic displacements in the structure. By contrast, a tight-binding approach allows a much simpler analysis. We illustrate the benefits of the tight-binding method by considering Ga(P,As:Bi) and GaNAs. We show that the tight-binding method provides a clear and quantitative explanation for many of the unusual electronic properties of these and related alloys, including the nonmonotonic variation of electron effective mass, me, and gyromagnetic ratio, ge, in GaNAs.

Photoelectric emission from a finite barrier quantum well formed in a GaAs film sandwiched between (Al,Ga)As layers

AbstractIn this communication an attempt is made to estimate the photoelectric current density from a finite barrier quantum well (QW) formed in an ultrathin film of semiconductor. The variation of electron effective mass in various energy levels of the conduction band has been considered in the present estimation. For computational purposes, the QW with rectangular potential of finite barrier has been modeled by a thin film of GaAs sandwiched between barrier layers of (Al,Ga)As, and the well depth has been varied by varying the Al concentration. Results have been compared with standard established results for photoelectric emission from ultrathin films of GaAs, where the rectangular QW was assumed to be infinitely deep. The quantized nature of the photoelectric current density provides a description of energy level structures in QWs of varying widths and depths – both finite and infinite. The results indicate that to make an electron participate in the emission process, higher incident photon energy is required in case of a finite QW with respect to that of an infinite QW. An enhanced photoelectric current density is also obtained in the former case. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron–acoustic phonon interaction in semiconductor nanostructures: Role of deformation variation of electron effective mass

We demonstrate that the phonon-induced variation of electron effective mass gives a substantial contribution to the electron--acoustic-phonon interaction in semiconductor nanostructures. Calculations are carried out for electrons in a quantum well (QW) and a quantum wire (QWR) of III-V heterostructure materials. This mechanism gives rise to an interference effect in electron scattering with longitudinal acoustic phonons via the deformation potential and allows the electrons to interact with transverse acoustic phonons. Due to these peculiarities, the additional channel of scattering can either increase or decrease the total scattering rate. For a given semiconductor, the modified scattering constant has been shown to depend on the dimensionality of the electron gas, the size and the shape of the nanostructure, and on the temperature. The scattering constants for intrasubband transitions in QW's and QWR's are different for the electron energy and momentum relaxation. For narrow QW's or flattened QWR's, modification of the commonly used bulk deformation potential interaction at low temperatures originates mainly due to interaction with transverse acoustic phonons. For GaAs QW of 50 \AA{} width, the ratio of the total relaxation rate of the electron energy to that from the bulk deformation potential coupling is about 0.65 for the temperature 4 K and 1.7 for 20 K.

Acoustic phonon bottleneck in quantum dots: role of deformation variation of electron effective mass

We demonstrate that phonon-induced variation of electron effective mass leads to a substantial increase of the electron–acoustic phonon interaction in semiconductor quantum dots. The contribution of this mechanism to electron scattering depends on a shape of the nanostructure. For dots of small sizes it exceeds the contribution of the conventional deformation potential and it prevents the reduction of the electron relaxation rate with decreasing dot size as predicted by the conventional theory.