Electronic structure, structural and optical properties of thermally evaporated CdTe thin films

TL;DR

This study investigates the structural, electronic, and optical properties of thermally evaporated CdTe thin films, combining experimental measurements with ab initio calculations to understand their electronic structure and optical behavior.

Contribution

It provides a comprehensive analysis of CdTe thin films, highlighting the effects of LDA and LDA+U approximations on electronic structure calculations and their impact on optical property predictions.

Findings

LDA underestimates the band gap and energy levels of Cd-4d states.

LDA+U corrects s-d coupling and shifts Cd-4d levels closer to experimental values.

Calculated optical spectra agree well with experimental data.

Abstract

Thin films of CdTe were deposited on glass substrates by thermal evaporation. From the XRD measurements itis found that the films are of zinc-blende-type structure. Transmittance, absorption, extinction, and refractive coefficients are measured. Electronic structure, band parameters and optical spectra of CdTe were calculated from ab initio studies within the LDA and LDA+U approximations. It is shown that LDA underestimates the band gap, energy levels of the Cd-4d states, s-d coupling and band dispersion. However, it calculates the spin-orbit coupling correctly. LDA+U did not increase much the band gap value, but it corrected the s-d coupling by shifting the Cd-4d levels towards the experimentally determined location and by splitting the LDA-derived single s peak into two peaks, which originates from admixture of s and d states. It is shown that the sd coupling plays an important role in absorption and reflectivity constants. The calculated optical spectra fairly agree with experimental data. Independent of wave-vector scissors operator is found to be a good first approximation to shift rigidly the band gap of CdTe underestimated by LDA.