W. Salejda

Stark effect in semiconductor quantum dots

A theory of the Stark effect in semiconductor quantum dots has been developed for the case of dominating polarization interaction of an electron and a hole with the nanocrystal surface. A shift of electron and hole quantum well levels in a nanocrystal in the interband absorption range in a uniform external electric field is determined by the quantum-confinement quadratic Stark effect. An electro-optical method is proposed, making it possible to estimate the characteristic quantum dot radius at which three-dimensional excitons can exist.

Polarized light transmission through generalized Fibonacci multilayers: I. Dynamical maps approach and II. Numerical results

Summary I. Dynamical maps approach: The theory of polarized light propagation in dielectric generalized Fibonacci multilayers is developed. The matrix formulation and dynamical maps technique is used. New objects: diagonal antitraces, symmetric and antisymmetric nondiagonal antitraces of characteristic matrices are introduced. Dynamical maps for these objects are derived. Transmittance for s- and p-type polarized light of the studied aperiodic multilayers placed between two homogenous media is expressed in terms of traces and antitraces of characteristic matrices. Three interesting physical situations are considered, allowing to study the influence of surrounding media on light transmission properties of Fibonacci-type multilayers. II. Numerical results: The theory of polarized light propagation in generalized Fibonacci multilayers, recently developed in the framework of matrix formulation and dynamical maps technique, is applied. Transmittance of studied systems is numerically calculated and presented in gray scale figures. The main tendencies in dependences of transmittance on model parameters are presented and discussed. We find a strong dependence of transmittance on refractive indices of surrounding media. We show that the proposed approach can be useful in optical engineering.

Negative differential resistance in aperiodic semiconductor superlattices

Influence of external DC electric field on the electron tunnelling through aperiodic semiconductor superlattices is studied numerically in the framework of generalized Kronig–Penney model and Landauer formalism. Spatial dependence of electron effective mass and dielectric constant as well as band non-parabolicity effects and non-abrupt interfaces are taken into account. Influence of model parameters on the Landauer resistance is investigated. Areas of negative differential resistance are found and presented as two-dimensional grayscale maps.

The Landauer conductance of generalised Fibonacci superlattices. Numerical results

The quantum model for quasi-one-dimensional generalised Fibonacci superlattices (GFS) is formulated. The Landauer electrical conductance σL of GFS is studied numerically. It is shown that σL as a function of incident particle energy E oscillates strongly and exhibits resonant character. We have verified numerically that σL(E) reaches its local maximum for E corresponding to energy eigenenvalues of charge in superlattices.

Electromagnetic wave propagation through aperiodic superlattices composed of left- and right-handed materials

Using the transfer matrix formalism and dynamical maps technique, we calculate numerically transmittance of polarized electromagnetic wave through aperiodic superlattices (generalized Fibonacci, generalized Thue-Morse, double-periodic and Rudin-Shapiro), built of left- and right-handed materials. In our calculations, strong dispersion of left-handed materials is taken into account, leading to tunnelling effects in a wide range of wavelengths and incidence angles. The results are presented in gray scale transmittance maps.

The Landauer resistance of generalized Fibonacci lattices: the dynamical maps approach

We study the electronic properties of the generalized Fibonacci lattices containing finite numbers of rectangular barriers distributed quasi-periodically. In the framework of the Kronig-Penney model we derive the dynamical maps which allow to calculate the Landauer resistance of the considered systems. The maps obtained are an extension of the existing results to: (1) the more general class of distributions of rectangular barriers; and (2) the case of complex unimodular matrices.

Photonic band structure of one-dimensional aperiodic superlattices composed of negative refraction metamaterials

The dispersion relation for polarized light transmitting through a one-dimensional superlattice composed of aperiodically arranged layers made of ordinary dielectric and negative refraction metamaterials is calculated with finite element method. Generalized Fibonacci, generalized Thue-Morse, double-periodic and Rudin-Shapiro superlattices are investigated, using their periodic approximants. Strong dispersion of metamaterials is taken into account. Group velocities and effective refraction indices in the structures are calculated. The self-similar structure of the transmission spectra is observed.

Two-dimensional Wannier-Mott exciton in a uniform electric field

A new treatment of the problem of a two-dimensional Wannier-Mott exciton in a uniform electric field, based on the parabolic coordinates, is presented. The quasi-stationary Hamiltonian is regularized, and the efficient numerical methods are applied. The dependence of the exciton binding energy on the electric field is computed. The results are very close to those obtained by the perturbation theory calculations.

Toward cloaking in nanosphere dispersed liquid crystal (NDLC) metamaterial

We discuss the concept of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry for TM polarization. The system consists of six layers of NDLC with different values of ordinary refractive index. Finite element calculations (COMSOL Multiphysics) show that scattering from the hidden object is strongly limited in the presence of the cloak.

Reverse engineering of AlxGa1−xAs/GaAs structures composition by reflectance spectroscopy

The paper presents the application of non-modulation reflectance method for composition profiling of epitaxial AlxGa−xAs/GaAs structures. This non-destructive method is based on spectral measurements and theoretical reflectance spectrum matching. This is a very accurate and sensitive method of determining the Al composition in AlxGa1−xAs layers and structures with resolution down to 1 nm. In this work, the authors describe theoretic principles of this method and present experimental results of characterization of different AlGaAs structures to prove the potential of the worked out method.