Structure, Morphology, Chemical Composition, and Optical Properties of Annealed Multilayer Ge/Al2O3 and Si/Ge/Si/Al2O3 Nanoperiodic Systems

The properties of multilayer (up to 80 layers) nanoperiodic (period up to similar to 12 nm) Al2O3/Ge and Al2O3/Si/Ge/Si systems annealed in a nitrogen atmosphere at temperatures from 700 to 900 degrees C are studiedusing transmission electron microscopy, X-ray techniques of photoelectron spectroscopy, diffractometry,and ref lectometry, and optical methods of photoluminescence and Raman scattering. In Al2O3/Ge samplesannealed at 700 degrees C, the formation of Ge nanocrystals with a size of similar to 3 nm is detected, which disappear at800-900 degrees C, when nanocrystals of the Al6Ge5 semiconductor phase of large size (> 100 nm) grow. The intro-duction of separating layers of Si (Al2O3/Si/Ge/Si) leads to the formation of nanocrystals of the SiGex alloyat a temperature of 800 degrees C, above which the size of the crystallites of this phase is about similar to 3-4 nm. The dataobtained using X-ray techniques are in good agreement with the results of high-resolution transmission elec-tron microscopy and Raman spectroscopy. In the Al2O3/Ge samples, photoluminescence is observed atroom temperature at similar to 2.1 eV, and in the Al2O3/Si/Ge/Si samples, there is an additional luminescence peakat similar to 1.4 eV. Hydrogenation of the samples by annealing in a hydrogen atmosphere at 500 degrees C enhances the lumi-nescence intensity.