Optical properties of ZnSe using linear response theory

The electronic structure and optical response of ZnSe are studied in this work. The studies are carried out using first-principles full-potential linearized augmented plane wave method. After settling the crystal structure, the electronic band structure of the ground state of ZnSe is calculated. Linear response theory is applied to study optical response considering bootstrap (BS) and the long range contribution (LRC) kernels for the first time. We also use the random phase and adiabatic local density approximations for comparison. A procedure based on empirical pseudopotential method is developed to find material dependent parameterαrequired in the LRC kernel. The results are assessed by calculating the real and imaginary parts of linear dielectric function, refractive index, reflectivity, and the absorption coefficient. Results are compared with other calculations and available experimental data. The results of LRC kernel findingαfrom the proposed scheme are encouraging and at par with the BS kernel.

Extracting quantitative dielectric properties from pump-probe spectroscopy

Optical pump-probe spectroscopy is a powerful tool for the study of non-equilibrium electronic dynamics and finds wide applications across a range of fields, from physics and chemistry to material science and biology. However, a shortcoming of conventional pump-probe spectroscopy is that photoinduced changes in transmission, reflection and scattering can simultaneously contribute to the measured differential spectra, leading to ambiguities in assigning the origin of spectral signatures and ruling out quantitative interpretation of the spectra. Ideally, these methods would measure the underlying dielectric function (or the complex refractive index) which would then directly provide quantitative information on the transient excited state dynamics free of these ambiguities. Here we present and test a model independent route to transform differential transmission or reflection spectra, measured via conventional optical pump-probe spectroscopy, to changes in the quantitative transient dielectric function. We benchmark this method against changes in the real refractive index measured using time-resolved Frequency Domain Interferometry in prototypical inorganic and organic semiconductor films. Our methodology can be applied to existing and future pump-probe data sets, allowing for an unambiguous and quantitative characterisation of the transient photoexcited spectra of materials. This in turn will accelerate the adoption of pump-probe spectroscopy as a facile and robust materials characterisation and screening tool.

Photoinduced changes in transmission, reflection and scattering prevent conventional pump-probe spectroscopy to unambiguously assign the origin of spectral signatures. Ashoka et al. have developed an optical modelling technique to extract quantitative and unambiguous changes in the dielectric function from standard pump-probe measurements.

A Systematic Study of Compositionally Dependent Dielectric Tensors of SnSxSe1-x Alloys by Spectroscopic Ellipsometry

We report the dielectric tensors on the cleavage plane of biaxial SnSxSe1-x alloys in the spectral energy region from 0.74 to 6.42 eV obtained by spectroscopic ellipsometry. Single-crystal SnSxSe1-x alloys were grown by the temperature-gradient method. Strongly anisotropic optical responses are observed along the different principal axes. An approximate solution yields the anisotropic dielectric functions along the zigzag (a-axis) and armchair (b-axis) directions. The critical point (CP) energies of SnSxSe1-x alloys are obtained by analyzing numerically calculated second derivatives, and their physical origins are identified by energy band structure. Blue shifts of the CPs are observed with increasing S composition. The fundamental bandgap for Se = 0.8 and 1 in the armchair axis arises from band-to-band transitions at the M0 minimum point instead of the M1 saddle point as in SnS. These optical data will be useful for designing optoelectronic devices based on SnSxSe1-x alloys.

Theoretical investigations of electronic, optical and mechanical properties for GaSb and AlSb semiconductors under the influence of temperature

In this paper we explore the effects of temperature on the electronic and mechanical properties of GaSb and AlSb semiconductors by using the local empirical pseudo-potential method. Our results show that the band gaps, refractive index, optical dielectric constant, elastic constants (C11, C12, C44), bulk modulus, shear modulus and Young modulus of these compounds vary with the change in temperature. The comparison of some of our results with the available experimental data confirms the accurateness of our theoretical approach, which also infers the reliability of our other theoretical results. As, for some of the present calculations a little experimental data is available for comparison, therefore these results can be used as a reference work in the future studies.