Drude-like behavior of Ge:Sb:Te alloys in the infrared

The optical transmittance of Ge:Sb:Te evaporated thin film alloys with different compositions was measured in the wavelength range from 2.5 to 34 μm. The as-deposited films with an amorphous structure were thermally crystallized to achieve the two known crystalline phases: the fcc and the hexagonal at higher treatment temperatures. There are drastic changes in the transmittance spectra of samples with different structural phase, which reflects the differences in their optical constants. For amorphous films, only the frequency independent term in Drude’s formula is required to properly describe their transmittance spectra. For samples in the hexagonal and the fcc structures, the transmittance spectra show a metallic and semimetallic behavior, respectively; therefore, the full Drude expression has been used as the general dispersion relation for the optical constants of the films. The electrical conductivity deduced from the Drude expression shows a dependence on Sb concentration in good agreement with previously reported values measured on bulk single crystals. Furthermore, the n and k spectra obtained in the measured infrared range are in good agreement with the values in the visible-UV region, previously measured using spectroscopic ellipsometry.