Effective mass (solid-state physics)

About: Effective mass (solid-state physics) is a research topic. Over the lifetime, 12539 publications have been published within this topic receiving 295485 citations.

Any l-state improved quasi-exact analytical solutions of the spatially dependent mass Klein–Gordon equation for the scalar and vector Hulthén potentials

Abstract: We present a new approximation scheme for the centrifugal term to obtain a quasi-exact analytical bound state solution within the framework of the position-dependent effective mass radial Klein?Gordon equation with the scalar and vector Hulth?n potentials in any arbitrary D dimension and orbital angular momentum quantum numbers l. The Nikiforov?Uvarov (NU) method is used in the calculations. The relativistic real energy levels and corresponding eigenfunctions for the bound states with different screening parameters have been given in a closed form. It is found that the solutions in the case of constant mass and in the case of s-wave (l=0) are identical with the ones obtained in the literature.

Gutzwiller-Hubbard lattice-gas model with variable density: Application to normal liquid 3He.

Abstract: The results of the Gutzwiller approach to a Hubbard lattice-gas model with a variable density of particles is used to describe the pressure dependence of thermodynamic properties of the ground state of normal liquid $^{3}\mathrm{He}$. The molar volume of the liquid is given by that of the underlying lattice and the filling factor n=1-\ensuremath{\delta} of the band, where \ensuremath{\delta} describes the deviation from half-filling. If the lattice is taken as incompressible, one finds that there exists a critical pressure at which a transition to a localized state occurs. The transition is accompanied by a disappearance of \ensuremath{\delta}, i.e., the transition only takes place at exactly half-filling. As the transition is approached, \ensuremath{\delta} and the density of doubly occupied sites are found to scale. The pressure dependence of the effective mass, the spin susceptibility and the compressibility is calculated. In a second model, the lattice is assumed to be compressible, shifting the critical pressure to much higher values. The on-site repulsion U is related to the microscopic soft-core potential ${f}_{0}^{s}$(r), which allows one to calculate the pressure dependence of the effective mass and the spin susceptibility. The absence of a localization transition for pressures of the order of the melting pressure of $^{3}\mathrm{He}$ leads to a smooth pressure dependence of the calculated quantities which are qualitatively borne out by experiment.

Band gap tunning in BN-doped graphene systems with high carrier mobility

Abstract: Using density functional theory, we present a comparative study of the electronic properties of BN-doped graphene monolayer, bilayer, trilayer, and multilayer systems. In addition, we address a superlattice of pristine and BN-doped graphene. Five doping concentrations between 12.5% and 75% are considered, for which we obtain band gaps from 0.02 eV to 2.43 eV. We show that the effective mass varies between 0.007 and 0.209 free electron masses, resembling a high mobility of the charge carriers.

Effective mass and collision time of (100) Si surface electrons

Abstract: The effective mass of electrons in (100) Si inversion and accumulation layers was measured by the temperature broadening of oscillatory magnetoconductance technique for a wide range of substrate doping level, geometry, and interface charge as well as various field-strength and substrate biases. It is shown that the apparent effective mass values are very sensitive to these parameters. Measurements were made at constant magnetic field but for varying oxide charge so that for a given magnetic field the effect of oxide-charge scattering could be eliminated by extrapolating to zero oxide charge. The result was remarkably a carrier-concentration independent mass of about 0.21. Collision broadening of the oscillations was studied to determine the scattering time $\ensuremath{\tau}$. The values of $\ensuremath{\tau}$ were found to be sensitive to the preexponential damping factor in H. The results are in fair agreement with the zero-field conductivity and average magnetoconductance measurements.

Low effective mass and carrier concentration optimization for high performance p-type Mg2(1−x)Li2xSi0.3Sn0.7 solid solutions

Abstract: Mg2Si1−xSnx solid solutions are promising thermoelectric materials for power generation applications in the 500–800 K range. Outstanding n-type forms of these solid solutions have been developed in the past few years with the thermoelectric figure of merit ZT as high as 1.4. Unfortunately, no comparable performance has been achieved so far with p-type forms of the structure. In this work, we use Li doping on Mg sites in an attempt to enhance and control the concentration of hole carriers. We show that Li as well as Ga is a far more effective p-type dopant in comparison to Na or K. With the increasing content of Li, the electrical conductivity rises rapidly on account of a significantly enhanced density of holes. While the Seebeck coefficient decreases concomitantly, the power factor retains robust values supported by a rather high mobility of holes. Theoretical calculations indicate that Mg2Si0.3Sn0.7 intrinsically possesses the almost convergent double valence band structure (the light and heavy band), and Li doping retains a low density of states (DOS) on the top of the valence band, contrary to the Ga doping at the sites of Si/Sn. Low temperature specific heat capacity studies attest to a low DOS effective mass in Li-doped samples and consequently their larger hole mobility. The overall effect is a large power factor of Li-doped solid solutions. Although the thermal conductivity increases as more Li is incorporated in the structure, the enhanced carrier density effectively shifts the onset of intrinsic excitations (bipolar effect) to higher temperatures, and the beneficial role of phonon Umklapp processes as the primary limiting factor to the lattice thermal conductivity is thus extended. The final outcome is the figure of merit ZT ∼ 0.5 at 750 K for x = 0.07. This represents a 30% improvement in the figure of merit of p-type Mg2Si1−xSnx solid solutions over the literature values. Hence, designing low DOS near Fermi level EF for given carrier pockets can serve as an effective approach to optimize the PF and thus ZT value.