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 M-0 minimum point instead of the M-1 saddle point as in SnS. These optical data will be useful for designing optoelectronic devices based on SnSxSe1-x alloys.

Automated summary

Dielectric tensors on the cleavage plane of biaxial SnSxSe1-x alloys were reported using spectroscopic ellipsometry in the energy region from 0.74 to 6.42 eV, revealing strongly anisotropic optical responses along different principal axes. An approximate solution provided anisotropic dielectric functions along zigzag and armchair directions. The blue shifts of critical point energies with increasing S composition were observed, and the fundamental bandgap for Se = 0.8 and 1 in the armchair axis was found to arise from band-to-band transitions at the M-0 minimum point.