Effects Of Nonparabolic Band Structure Research Articles

Determination of electron effective mass in InN by cyclotron resonance spectroscopy

Abstract We report the determination of electron effective mass in InN by using cyclotron resonance (CR) spectroscopy. To avoid the influence of sapphire substrate on CR measurements, InN epilayer with low residual electron concentration of 5 × 1017 cm−3 was grown on silicon substrate. Together with analyzing the effect of non-parabolic band structure, we derive that the isotropy c-plane electron effective mass of InN epilayer is 0 . 0 50 ± 0.0 0 2 m0 and 0 . 0 58 ± 0.0 0 2 m0 at temperatures of 4.2 and 50 K, respectively, which is in good agreement with our theoretical predication of the effective mass near the Γ point.

Direct observation of the band gap shrinkage in amorphous In2O3–ZnO thin films

We investigated the dependence of valence- and core-level photoemission spectra of amorphous In2O3–ZnO (a-IZO) films on carrier density by using hard x-ray photoemission spectroscopy (hν=8000 eV). The valence band edge distinctly shifts toward high binding energy with the increase in carrier density from 0.80 to 3.96 × 1020 cm−3, and an abrupt jump for the shift of the valence band edge from high to low binding energy occurs at a carrier density of 4.76×1020 cm−3. After considering the effect of nonparabolic bandstructure, the shifts are still less than the width of the occupied conduction band, providing direct evidence for the band gap shrinkage. Our calculation results indicate that the contribution of the band gap shrinkage increases as the carrier density increases, which accords with the observations in doped conducting crystal materials, such as Sn doped In2O3. Moreover, it is found that the conduction electrons of a-IZO films are strongly perturbed by the ionization of core levels, which leads to obvious plasmon satellites in core photoemission spectra lines.

Fullband Simulation of Nano-Scale MOSFETs Based on a Non-equilibrium Green's Function Method

The analysis of multiband quantum transport simulation in double-gate metal oxide semiconductor field effects transistors (DGMOSFETs) is performed based on a non-equilibrium Green's function (NEGF) formalism coupled self-consistently with the Poisson equation. The empirical sp3s* tight binding approximation (TBA) with nearest neighbor coupling is employed to obtain a realistic multiband structure. The effects of non-parabolic bandstructure as well as anisotropic features of Si are studied and analyzed. As a result, it is found that the multiband simulation results on potential and current profiles show significant differences, especially in higher applied bias, from those of conventional effective mass model.

Non-equilibrium Green’s function method for modeling quantum electron transport in nano-scale devices with anisotropic multiband structure

Aggressive scaling of devices has reduced device dimensions into nanometer scale in which the single-band effective mass model is inadequate to simulate quantum transport in such devices. Thus it motivates the use of more realistic full band structures in quantum transport simulations. In this study we perform the analysis of multiband quantum transport in nanoscale devices based on a non-equilibrium Green’s function (NEGF) formalism coupled self-consistently with the Poisson equation. The empirical nearest neighbor sp3s* tight binding approximation (TBA), where the couplings among atomic orbitals of the host crystal are taken into account, is employed to obtain a realistic multiband structure. The effects of non-parabolic bandstructure as well as anisotropic features of Si are studied and analyzed. Our multiband simulation results on potential and current profiles show significant differences, especially in higher applied bias, with those of conventional effective mass model where only parabolic singleband is considered in the simulation.

Nonparabolicity effects on electron-confined LO-phonon scattering rates in GaAs-Al0.45Ga0.55As superlattice

theoretically the effect of non-parabolic band structure on the electron-confined LO-phonon scattering rate in GaAs- Al0.45Ga0.55As superlattice using the quantum treatment, the new wave function of electron miniband conduction of superlattice and a reformulation slab model for the confined LO-phonon modes. An expression for the scattering rates is obtained. Our results show that for transitions due to the emission of confined LO-phonon the scattering rates significantly increase for non-parabolicity case.

An efficient solution of the Boltzmann transport equation which includes the Pauli exclusion principle

Nonequilibrium distribution functions for both degenerate and nondegenerate electron ensembles are obtained from efficient solutions to a Boltzmann transport equation for Si. The distribution function is taken to be expressible as a Legendre polynomial expansion, which is substituted into a Boltzmann equation that incorporates the effects of nonparabolic band structure, inelastic phonon scattering and the Pauli exclusion principle. The resulting Boltzmann equation takes on a nonlinear form which is quickly solved by means of the numerical Newton-Raphson method with appropriate boundary conditions. The resulting distribution function approaches the Fermi-Dirac function in the limit of high electron concentration and low electric field. In low probability ranges, which are found at high energies, the distribution function takes on the character of the Boltzmann distribution. Using average energy as a guideline, the values of electric field and carrier concentration which require consideration of the Pauli exclusion principle in electron transport investigations for Si are provided. In addition to providing a technique for investigating the effects of degeneracy, the efficiency of the new method facilitates its use in CAD tools for semiconductor devices.

Efficient calculation of ionization coefficients in silicon from the energy distribution function

A method for calculating impact ionization coefficients by solving the Boltzmann transport equation is presented. The distribution function is taken to be expressible as a Legendre polynomial expansion, which is substituted into a Boltzmann equation that incorporates the effects of nonparabolic band structure, deformation-potential phonon scattering, and impact ionization. The resulting Boltzmann equation can be expressed in a linear form, and solved using sparse-matrix difference-differential methods. Ionization coefficients are obtained directly from the distribution function. Calculated values for the ionization coefficients agree very well with experiment for electrons in silicon.

The effects of non-parabolic band structure on Auger transition rates in bulk semiconductors, quantum wells and quantum well wires

A new approach to the problem of including non-parabolic band structure in calculations of Auger recombination rates is presented, giving results for quantum wells (QW) that are readily generalised to the cases of bulk semiconductors and quantum well wires (QWW). The band structure in the region of the excited Auger carrier is described using non-local pseudopotential band structure, whereas the other carriers, being close to their respective band edges, are described using parabolic bandstructure. The authors' approach differs from earlier work in that the energies and wavevectors of carriers close to the band edges are not neglected, but simple analytic results are obtained. Numerical results for the effects of non-parabolic band structure on bulk Auger transition rates in GaAs and GaSb, using the simple expressions derived in this paper, are found to be in good agreement with other calculations.

Effect of non-parabolic band structure on amplification of surface phonons in n-type InSb films

The effect of non-parabolic band structure of surface phonons in n-type InSb films has been investigated quantum mechanically in the GHz frequency region. Numerical results show that the amplification coefficient is enhanced for the non-parabolic band structure due to the non-linear nature of the energy band in semiconductors. Moreover, the amplification coefficient depends also on the temperature, the piezoelectric coupling mechanisms, the frequency of sound waves, the electric field, and the thickness of the semiconductor film.

Effect of nonparabolic band structure of semiconductors on acoustoelectric instability

Effect of nonparabolic band structure of semiconductors on acoustoelectric instability

Effect of nonparabolicity on transverse magnetoresistance of semiconductors in strong magnetic fields

The effect of nonparabolic band structure on the transverse magnetoresistance in a semiconductor such as $n$-type InSb in the presence of a dc magnetic field is studied taking into account the inelasticities in the electron-phonon scattering. We discuss this effect of nonparabolicity in semiconductors for both deformation-potential coupling and piezoelectric coupling to acoustic phonons. Results show that the numerical values of the transverse magnetoresistance for the case of the piezoelectric coupling are much smaller than those for the case of the deformation-potential coupling. Therefore, the deformation-potential coupling mechanism plays the dominant role for the transverse magnetoresistance in strong magnetic fields in $n$-type InSb. We also found that the nonparabolicity of the energy-band structure will change the effect of the temperature on the transverse magnetoresistance besides the enhancement of its magnitude. Our numerical results are found to be in qualitative agreement with experimental results in the quantum limit.

Effect of Nonparabolic Band Structure on Longitudinal Magnetoacoustic Phenomena

The effect of nonparabolic band structure on the propagation of ultrasound in a semiconductor such as $n$-type InSb in the presence of longitudinal magnetic fields is discussed using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The absorption coefficient and sound velocity for ultrasound propagating parallel to the magnetic field are found to change with magnetic field. This dependence on magnetic field arises solely from the nonparabolicity of the energy bands and would be in addition to any magnetic field dependence due to a field-dependent relaxation time. A numerical calculation is performed for the case of $n$-type InSb and a comparison is made with the experimental results of Nill and McWhorter.