Ellipsometric study of optical properties of GaSxSe1-x layered mixed crystals

• Ellipsometry measurements were carried out in the 1.2–6.2 eV spectral range.
• Spectral dependence of optical constants ε1, ε2, n and k was obtained.
• Second derivative spectra of dielectric function revealed interband transitions.
• The variation of critical point energies with composition (x) was also plotted.

Spectroscopic ellipsometry measurements were performed on GaSxSe1-x mixed crystals (0 ⩽ x ⩽ 1) in the 1.2–6.2 eV range. Spectral dependence of optical parameters; real and imaginary components of pseudodielectric function, pseudorefractive index and pseudoextinction coefficient were reported in the present work. Critical point (CP) analyses on second-energy derivative spectra of the pseudodielectric function were accomplished to find the interband transition energies. The revealed energy values were associated with each other taking into account the fact that band gap energy of mixed crystals rises with increase in sulfur content. The variation of CP energies with composition (x) was also plotted. Peaks in the spectra of studied optical parameters and CP energy values were observed to be shifted to higher energy values as sulfur concentration is increased in the mixed crystals.

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