Research On Sputtering Multilayer Ge/Si Quantum Dot

The self-assembly Ge/Si quantum dots grown on Si substrate shows many unique optical and electrical properties. These properties will play an important role in fabricating the new microelectronics and optoelectronics devices. Moreover, Si-based Ge quantum dots can be compatible with the mature Silicon integrated circuit technology, so the fabrication of Ge/Si quantum dots has more special significance. Molecular beam epitaxy (MBE) and chemical vapor deposition (CVD) are two main methods of self-organized growth of Si-based Ge quantum dots at present. In addition, ion beam sputtering deposition (IBSD) is used to prepare quantum dots in recent years. It has been demonstrated that growing multilayer structures is an effective way to control the growth of quantum dots. On the one hand, it can increase the number of quantum dots per unit volume, which is helpful for the application of quantum dot devices. On the other hand, the elastic strain fields created by buried islands will mediate the growth of islands on the upper layer. Suitable experimental conditions, after repeated a certain number, the size uniformity of islands can be greatly improved by growing multilayer structures. However, the growth parameters of Si spacer-layer and deposition conditions of Ge will be important influencing factors in the structure.In this thesis, Ge/Si quantum dots were prepared by ion beam sputtering technique, and the study work mainly composed with following aspects:1. A series of double-layer Ge/Si quantum dots were prepared on Si(100) substrate by ion beam sputtering system. The influence of the growth temperature of Si spacer-layer on the upper layer quantum dots is investigated by atomic force microscopy(AFM) and Raman spectra. The results show that the size of islands on the second layer decreases and the density first increases and then decreases, with increasing growth temperature of Si spacer-layers. In this article, an optimum growth temperature of Si spacer-layer is obtained by analyzing the AFM pictures and Raman spectra.2. Double-layer Ge/Si quantum dots were prepared by ion beam sputtering deposition on Si (100) substrates. The influences of deposition thickness of Si spacer-layer on the microstructure of double-layer Ge/Si quantum dots were characterized by Atomic force microscopy (AFM) and Raman spectra technique. The results indicate that increasing the thickness of Si spacer-layer, the islands merger phenomenon disappears. When the deposition thickness is larger than40nm, the islands on the upper-layer show the same features with the buried islands. The mechanism of three-factor interactions of nano-islands is proposed to explain these phenomena.3. A series of single-layer and double-layers Ge/Si quantum dots samples with different Ge thickness were grown on Si(100) substrate by ion beam sputtering system. AFM and Raman spectroscopy were employed to characterize the evolution of surface islands in the different structure, and study the influence of buried strain on the growth of islands on the upper layer. The results show that a reduction of wetting-layer thickness of islands on the upper layer. In addition, with increasing the thickness of Ge deposition, the growth of islands on the second layer is modulated. Increasing the thickness of spacer-layer, the growth of islands on the second layer follows the buried dots. The change of growth mode is explained by the non-uniform strain field induced by the buried islands and passing through the spacer-layer.