Example 1: Amorphous Silicon on Oxidized Silicon Substrate .28a-Si.2FSiO2.2FSi-Sub.29 Refractive index and extinction coefficient of thin film materials

example 1 shows 1 broad maximum in n(λ) , k(λ) spectra of a-si film, expected amorphous materials. material transitions toward crystallinity, broad maximum gives way several sharper peaks in n(λ) , k(λ) spectra, demonstrated in graphics.

when measurement involves 2 or more films in stack of films, theoretical expression reflectance must expanded include n(λ) , k(λ) spectra, plus thickness, t, of each film. however, regression may not converge unique values of parameters, due non-linear nature of expression reflectance. helpful eliminate of unknowns . example, n(λ) , k(λ) spectra of 1 or more of films may known literature or previous measurements, , held fixed (not allowed vary) during regression. obtain results shown in example 1, n(λ) , k(λ) spectra of sio2 layer fixed, , other parameters, n(λ) , k(λ) of a-si, plus thicknesses of both a-si , sio2 allowed vary.