Studies on In_x(As₂Se₃)_1-x thin films using variable angle spectroscopic ellipsometry (VASE)

The results of multi-angle ellipsometrical measurements of thermally evaporated In_x(As₂Se₃)_1-x (x = 0, 0.01,0.05) films are presented. Optical parameters n and E_s of thin In_x(As₂Se₃)_1-x films show that indium atoms were incorporated into the host matrix of As₂Se₃ forming distinct features depending on the indium concentration. Refractive index, n, was found to decrease with the addition of In to the binary As₂Se₃. The real and imaginary parts of the dielectric function, ε' and ε" were also calculated from the obtained data and correlated with In concentration. It was found that e' decreases with the increase of In content while ε" increases with the increase of In content. Absorption edge is shifted towards lower photon energy with the increase of In content. As a result, the optical energy gap decreases with increasing In content. This has been correlated with the chemical character of the additive as well as with the structural and bonding aspects of the amorphous composition. Nonlinear optical constants (χ⁽³⁾ and n₂) were determined from linear optical parameters using semi-empirical relations in the long wavelength limit.