tailieunhanh - Báo cáo hóa học: " Formation of Nanopits in Si Capping Layers on SiGe Quantum Dots"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: IFormation of Nanopits in Si Capping Layers on SiGe Quantum Dots | Cui et al. Nanoscale Res Lett 2011 6 59 http content 6 1 59 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Formation of Nanopits in Si Capping Layers on SiGe Quantum Dots Jian Cui Jian Hui Lin Yue Qin Wu Yong Liang Fan Zhenyang Zhong Xin Ju Yang Zui Min Jiang Abstract In-situ annealing at a high temperature of 640 C was performed for a low temperature grown Si capping layer which was grown at 300 C on SiGe self-assembled quantum dots with a thickness of 50 nm. Square nanopits with a depth of about 8 nm and boundaries along 110 are formed in the Si capping layer after annealing. Crosssectional transmission electron microscopy observation shows that each nanopit is located right over one dot with one to one correspondence. The detailed migration of Si atoms for the nanopit formation is revealed by in-situ annealing at a low temperature of 540 C. The final well-defined profiles of the nanopits indicate that both strain energy and surface energy play roles during the nanopit formation and the nanopits are stable at 640 C. A subsequent growth of Ge on the nanopit-patterned surface results in the formation of SiGe quantum dot molecules around the nanopits. Introduction Heteroepitaxy has been a powerful method to fabricate functional quantum structures e. g. quantum wells 1 quantum dots QDs 2 and quantum rings QRs 3 4 . On the one hand strain is the most important factor affecting the formation of nanostructures 1-3 and even their capping layers in heteroepitaxy 5 . The evolution of the strain can result in a variety of nanostructures such as QRs 3 . On the other hand strain induced by heteroepitaxy has been a very prominent improvement in technology to increase carrier mobility 6 . Recently strained Si channel induced by SiGe QDs has been proposed to enhance hole mobility in field effect transistors 7 . Thus strain together with its distribution and evolution is a key to understand the growth mechanism of the quantum