Optical properties of amorphous GeTe, Sb2Te3, and Ge2Sb2Te5: The role of oxygen

Amorphous films of GeTe, Sb2Te3, and Ge2Sb2Te5 were grown to thicknesses of 0.3–3μm using rf sputtering. The optical properties of these films are influenced by the presence of oxygen impurities. The absorption edge in these glasses is sometimes broader than in “standard” chalcogenide glasses, such as GeSe2 or As2Se3. This result implies either that the valance band consists of highly strained bonds or that large densities of defects exist. In some samples, there exists an electron paramagnetic resonance signal in the absence of any optical excitation, which implies that a large defect density (∼1019cm−3) exists within the energy gap. Below the optical gap the refractive index for Ge2Sb2Te5 is approximately 3.5. Electron spin resonance signals associated with the glassy SiO2 interface with the chalcogenide films are also observed.