Tuning the properties of Ge and Si nanocrystals based structures by tailoring the preparation conditions Review.

Ge and Si nanocrystals (NCs), quantum dots (QDs), and amorphous nanoparticles (NPs) have a significant role in the developement of micro- and nanoelectronic devices due to capability to tune their electrical and photoconductive properties by tailoring the morphology and structure parameters. Ge and Si NCs/QDs/NPs are zero-dimensional (0D) systems and the SiO2 films containing them are percolative systems. In this review, the role of deposition and annealing conditions in the morphology and structure of Ge and Si NCs/QDs/NPs embedded in amorphous SiO2 matrix is discussed for a wide variety of films and multilayered structures. The electrical and photoconductive properties of nanostructures deposited by different techniques as magnetron sputtering, ion implantation, chemical vapour deposition, sol-gel and molecular beam epitaxy, and subsequently annealed in conventional furnace or by rapid thermal annealing under different conditions are analised. We demonstrate how the electrical and photoconductive properties of nanostructures can be tuned by varying the deposition and annealing parameters. The role of Si-rich oxide and defects in the formation of Ge and Si NCs is shown and the role of defects in improving electrical properties and enhancing the photoconductivity of films and multilayered structures is highlighted. We evidence the contribution of quantum confinement effect and show that the most probable transport mechanisms in these percolative systems are tunnelling and hopping. [ABSTRACT FROM AUTHOR]