Parameterization of the dielectric functions of InGaSb alloys

Analytic expressions are presented that accurately represent the dielectric functions ε = ε1 + iε2 of In1−xGaxSb from 1.5 to 6 eV. We used the parametric model, which portrays ε as a sum of polynomials and can accommodate the asymmetric nature of critical point transitions. The ε spectra were obtained previously by spectroscopic ellipsometry for x = 0.000, 0.102, 0.305, 0.473, 0.684, and 1.000. The ε data are successfully reconstructed and parameterized by eight polynomials. With the interpolation of parameters of ε spectra, we can determine ε as a continuous function of Ga composition and energy over the entire composition range 0 ≤ x ≤ 1. These results should be useful for device design and in situ monitoring of deposition.