Dynamic Coupling of Piezoelectric Effects, Spontaneous Polarization, and Strain in Lattice-Mismatched Semiconductor Quantum-Well Heterostructures

A static and dynamic analysis of the combined and self-consistent influence of spontaneous polarization, piezoelectric effects, lattice mismatch, and strain effects is presented for a three-layer one-dimensional AlN/GaN wurtzite quantum-well structure with GaN as the central quantum-well layer . It is shown that, contrary to the assumption of Fonoberov and Balandin [J. Appl. Phys. 94, 7178 (2003); J. Vac. Sci. Technol. B 22, 2190 (2004)], even in cases with no current transport through the structure, the strain distributions are not well captured by minimization of the strain energy only and not, as is in principle required, the total free energy including electric and piezoelectric coupling and spontaneous polarization contributions. Furthermore, we have found that, when an ac signal is imposed through the structure, resonance frequencies exist where strain distributions are even more strongly affected by piezoelectric-coupling contributions depending on the amount of mechanical and electrical losses in the full material system

Second harmonic generation and birefringence of some ternary pnictide semiconductors

A first-principles study of the birefringence and the frequency dependent second harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC$_2$ (A = Zn, Cd; B = Si, Ge; C = As, P) with the chalcopyrite structures was carried out. We show that a simple empirical observation that a smaller value of the gap is correlated with larger value of SHG is qualitatively true. However, simple inverse power scaling laws between gaps and SHG were not found. Instead, the real value of the nonlinear response is a result of a very delicate balance between different intraband and interband terms.Comment: 13 pages, 12 figure

Electronic structure of helically coiled carbon nanotubes

AbstractIn the present work we calculate the electronic band structure of single-wall helical carbon nanotubes following an effective-mass approach. We include curvature effects and strain due to bending in the band structure. The curvature energy ΔE, and the change in the electronic energy ΔEs due to strain, depend upon the coil pitch and coil diameter of the tube. We find 0.003 ≤|ΔE|≤ 1.3 eV and 0 ≤ΔEs ≤ 4.0 eV for the single-wall helical carbon nanotubes considered here.</jats:p

Electrostriction coefficients of GaN, AlN, MgO and ZnO in the wurtzite structure from first-principles

International audienceFirst-principles calculations have been performed on wurtzite AlN, GaN, MgO and ZnO, with a view to obtaining electrostriction coefficients. © 2009 American Institute of Physics

Spurious solutions and boundary conditions in k center dot p theory

It is well known that the origin of one type of spurious solutions in multiband k(.)p theory is the failure to restrict the Fourier coefficients of the envelope functions to the first Brillouin zone. Often, the set of differential equations obtained is supplemented with interfacial boundary conditions derived by integrating the differential equations across the interface; however, this leads to a mathematically ill-posed problem as the envelope functions cannot simultaneously fulfill these boundary conditions and the requirement that the Fourier coefficients be restricted to the first Brillouin zone. We show, by way of an example, the origin of these spurious solutions and how to remove them

Accounting for Nonlinearities in Mathematical Modelling of Quantum Dot Molecules

Nonlinear mathematical models are becoming increasingly important for new applications of low-dimensional semiconductor structures. Examples of such structures include quasi-zero-dimensional quantum dots that have potential applications ranging from quantum computing to nano-biological devices. In this contribution, we analyze presently dominating linear models for bandstructure calculations and demonstrate why nonlinear models are required for characterizing adequately opto- electronic properties of self-assembled quantum dots