Example 4: Multi-Spectral Analysis of Germanium .2840.25.29-Selenium .2860.25.29 Thin Films Refractive index and extinction coefficient of thin film materials

when dealing complex films, in instances parameters cannot resolved uniquely. constrain solution set of unique values, technique involving multi-spectral analysis can used. in simplest case, entails depositing film on 2 different substrates , simultaneously analyzing results using forouhi-bloomer dispersion equations.

for example, single measurement of reflectance 190 nm - 1000 nm of ge40se60/si not provide unique n(λ) , k(λ) spectra of film. however, problem can solved depositing same ge40se60 film on substrate, in case oxidized silicon, , simultaneously analyzing measured reflectance data determine:

thickness of ge40se60/si film on silicon substrate 34.5nm,
thickness of ge40se60/si film on oxidized silicon substrate 33.6nm,
thickness of sio2 (with n , k spectra of sio2 held fixed), and
n , k spectra, 190 - 1000 nm, of ge40se60/si.