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

Abstract

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.

Tunability in the optoelectrical performance of n-SnS(1−x)Sex thin films for photovoltaic applications

“…The alloy SnSSe has received more attention because its band gap can be easily tuned by the composition between the band gap of SnS and SnSe. [17][18][19][20][21] Thus, the preparation of the SnSSe alloy is interesting from band-gap engineering and optoelectronic points of view.…”