Dielectric function of CuBrxI1-x alloy thin films

We study the dielectric function of CuBrxI1-x thin film alloys using spectroscopic ellipsometry in the spectral range between 0.7 eV and 6.4 eV, in combination with first-principles calculations based on density functional theory. Through the comparison of theory and experiment, we attribute features in the dielectric function to electronic transitions at specific k-points in the Brillouin zone. The observed band gap bowing as a function of alloy composition is discussed in terms of different physical and chemical contributions. The band splitting at the top of the valence band due to spin-orbit coupling is found to decrease with increasing Br-concentration, from a value of 660 meV for CuI to 150 meV for CuBr. This result can be understood considering the contribution of copper d orbitals to the valence band maximum as a function of the alloy composition.

Automated summary

We studied the dielectric function of CuBrxI1-x thin film alloys using spectroscopic ellipsometry and density functional theory calculations. The features in the dielectric function were attributed to electronic transitions at specific k-points in the Brillouin zone, and the band gap bowing was discussed in terms of physical and chemical contributions. The band splitting at the top of the valence band decreased with increasing Br-concentration, which can be understood by considering the contribution of copper d orbitals to the valence band maximum.