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.

Recent Studies on Rutile (TiO2)

Abstract: A review is made of the work on reduced and ``doped'' rutile performed since the appearance of Grant's survey article in the Reviews of Modern Physics (1958). Measurements of electrical and optical properties, and of electron spin resonance spectra are discussed. A model of electronic bound states and conduction levels is suggested that is compatible with the results of these experiments. There is strong evidence that the defects in reduced rutile are interstitial Ti3+ ions. At very low temperatures, nearly all electrons are self‐trapped on cation sites (polarons). As the temperature increases, some of these trapped electrons will be excited into the conduction band. The activation energy for this process is approximately 0.007 ev below 50°K, and about one order of magnitude higher around room temperature. It is concluded that conduction takes place in a narrow 3d band associated with Ti ions; the effective mass at the bottom of this band is ∼25m0. If one assumes that the polaron binding energy can be des...

The Effect of General Strain on the Band Structure and Electron Mobility of Silicon

Abstract: A model capturing the effect of general strain on the electron effective masses and band-edge energies of the lowest conduction band of silicon is developed. Analytical expressions for the effective mass change induced by shear strain and valley shifts/splittings are derived using a degenerate kldrp theory at the zone-boundary X point. Good agreement to numerical band- structure calculations using the nonlocal empirical pseudopotential method with spin-orbit interactions is observed. The model is validated by calculating the bulk electron mobility under general strain with a Monte Carlo technique using the full-band structure and the proposed analytical model for the band structure. Finally, the impact of strain on the inversion-layer mobility of electrons is discussed.

DFT and k · p modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells

Abstract: 3D hybrid organic perovskites, CH3NH3PbX3 (X = halogen), have recently been used to strongly improve the efficiency of dye sensitized solar cells (DSSC) leading to a new class of low-cost mesoscopic solar cells. CsSnI3 perovskite can also be used for hole conduction in DSSC. Density functional theory and GW corrections are used to compare lead and tin hybrid and all-inorganic perovskites. The room temperature optical absorption is associated to electronic transitions between the spin–orbit split-off band in the conduction band and the valence band. Spin–orbit coupling is about three times smaller for tin. Moreover, the effective mass of relevant band edge hole states is small (0.17). The high temperature phase sequence of CsSnI3 leading to the room temperature orthorhombic phase and the recently reported phases of CH3NH3MI3 (where M = Pb, Sn) close to the room temperature, are also studied. Tetragonal distortions from the ideal cubic phase are analysed by a k · p perturbation, including spin–orbit effect. In addition, the non-centrosymmetric phases of CH3NH3MI3 exhibit a splitting of the electronic bands away from the critical point. The present work shows that their physical properties are more similar to conventional semiconductors than to the absorbers used in DSSC. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Anisotropic mass density by two-dimensional acoustic metamaterials

Abstract: We show that specially designed two-dimensional arrangements of full elastic cylinders embedded in a nonviscous fluid or gas define (in the homogenization limit) a new class of acoustic metamaterials characterized by a dynamical effective mass density that is anisotropic. Here, analytic expressions for the dynamical mass density and the effective sound velocity tensors are derived in the long wavelength limit. Both show an explicit dependence on the lattice filling fraction, the elastic properties of cylinders relative to the background, their positions in the unit cell, and their multiple scattering interactions. Several examples of these metamaterials are reported and discussed.

Electronic structure and transport in thermoelectric compounds AZn2Sb2 (A = Sr, Ca, Yb, Eu).

Abstract: The AZn2Sb2 (Pm1, A = Ca, Sr, Eu, Yb) class of Zintl compounds has shown high thermoelectric efficiency (zT∼ 1) and is an appealing system for the development of Zintl structure–property relationships. High temperature transport measurements have previously been conducted for all known compositions except for SrZn2Sb2; here we characterize polycrystalline SrZn2Sb2 to 723 K and review the transport behavior of the other compounds in this class. Consistent with the known AZn2Sb2 compounds, SrZn2Sb2 is found to be a hole-doped semiconductor with a thermal band gap ∼ 0.27 eV. The Seebeck coefficients of the AZn2Sb2 compounds are found to be described by similar effective mass (m* ∼ 0.6 me). Electronic structure calculations reveal similar m* is due to antimony p states at the valence band edge which are largely unaffected by the choice of A-site species. However, the choice of A-site element has a dramatic effect on the hole mobility, with the room temperature mobility of the rare earth-based compositions approximately double that found for Ca and Sr on the A site. This difference in mobility is examined in the context of electronic structure calculations.