Multi-layered nanosized Al2O3/Ge/Si structures manufactured by electron-beam evaporation and annealed at a temperature within the range 700−900◦C are examined using transmission electron microscopy, Raman spectroscopy and X-ray diffraction techniques. The periodic structure with a good layer planarity is confirmed to retain after heat treatment up to 900◦C. At an annealing temperature above 700◦C, nanocrystallites with a bimodal size distribution start to form within initially amorphous Ge layers, the mean size of small crystallites being determined by Ge layer thickness and annealing temperature. An essential loss of Ge from multi-layered structure after 900oC anneal and development of Ge1−x Six solid solution with x up to 0.07 in the nanocrystallites is revealed.

Structures with Ge/Si nanoparticles (quantum dots) in an alumina matrix are interesting for researchers due to the combination of two main semiconductors, as well as the use of a matrix with high dielectric permittivity and strong oxygen oxygen–metal bonding. Nanoperiodic multilayer structures in the sequence substrate/Al2O3/Ge/Si/Al2O3 . . .Al2O3 (period — Al2O3/Ge/Si, the number of periods was up to 20) annealed at different temperatures were prepared in this work. It was shown that nanocrystalline particles of both Ge and Si were observed in the structures after annealing. Nanocrystal sizes and quantity were determined by the thicknesses of deposited layers and the annealing temperatures. The results obtained by various optical techniques indicate a quantum-size effect in the structures, which is confirmed by high-resolution microscopy.

AbstractThe problem of the optimal choice of parameters of the empirical tight-binding method to simulate the quantum-confined levels of Si nanocrystals embedded into an amorphous SiO_2 matrix is studied. To account for tunneling from nanocrystals to SiO_2, the amorphous matrix is considered as a virtual crystal with a band structure similar to that of SiO_2 β-cristobalite and with a lattice constant matched to the lattice constant of bulk Si. The electron density distributions in k space for electrons and holes quantum-confined in a Si nanocrystal in SiO_2 are calculated in a wide energy region, which provides a means to see clearly the possibility of the existence of efficient direct optical transitions for hot electrons at the upper quantum-confined levels.

Обзор посвящен моделированию нанокристаллов Si и Ge методом сильной связи. Сначала приведeн краткий обзор методов моделирования и результатов, полученных для кремниевых и германиевых нанокристаллов. Затем подробно описан метод моделирования сильной связью в варианте с учeтом орбиталей s,p,d,s* и представлены результаты, полученные на его основе для нанокристаллов кремния и германия. DOI: 10.21883/FTP.2017.10.45009.8605