Embedded In The Preparation And Properties Of Germanium Nanocrystals In The Dielectric Film

In this thesis, we have studied the Ge nanocrystals embedded in SiO₂ films which wrere prepared using magnetron sputtering and subsequent thermal annealing. Some influential factors on the structures of Ge nanocrystals, which include annealing temperature, Ge content, and so on, are studied. Multilayered Ge nanocrystals embedded in SiO_xGeN_y films have been fabricated on Si substrate by a superlattice approach. This approach significantly improved the density of Ge nanocrystals and ameliorated both the size and spatial distribution uniformity. The structure properties of the fabricated samples were investigated by X-ray diffraction (XRD), Raman spectrum and transmission electron microscopy (TEM). The following conclusions were obtained:1. Raman spectras were fitted by phonon confinement model (RWL model), and the size of Ge nanocrystals have been obtained. There are discrepancies of peak position between the fitted and experimental Raman curves. The compressive stress was analysed using XRD data. Our study showed that the compressive stress mainly causes the peak position discrepancy between fitted Raman curve and experimantal curve.2. Annealing temperature has an important influence on the structure of Ge nanocrystals. In the experiment, we found that Ge atoms start to crystallize when temperature reachs 750℃. At the Same condition, the size of Ge nanocrystals increased as the annealing temperature rised. But at higher temperature, both the size and the quantity of Ge nanocrystals reduced. A appropriate annealing temperature is important to obtain high quality composite films. The best annealing temperature of the samples we fabricated is about 900℃.3. At the same condition, the size and quantity of Ge nanocrystals were improved as increasing of Ge content in the Ge+SiO₂ composite target. The phenomena of Si crstallizing has been found at the low Ge content condition. Ge content and the best anneealing temperature restrict each other. As Ge content increasing, the maximun size of Ge nanocrystals enlarged, and the higher annealing temperature is needed to obtain the maximum size of Ge nanocrystals.4. After Ge nanocrystals formed in the composite film, preferred orientation of Si(111) appeard. The higher annealing temperature,the preferrd oritenation is more obvious.5. Superlattice approach was be brought forward first time. A 20 bi-layers (Ge+SiO₂)/SiO_xGeN_y superlattice structure was grown with abternate doposition of these two layers. The experiment results show that the Ge nanocrystal were confined within the (Ge+SiO₂) layers, and their size is defined by the (Ge+SiO₂) layer thickness. The denesity, size and spatial distribution of nanocrystals can be controlled by the multilayered superlattiec method.