Growth And Characterization Of Si Based Nanostructures And Functional Oxide Films

With the development of semiconductor technology, two challenges emerge. On the one hand, with the integration density increasing, the size of single devices decreases dramatically. The size has been close to the physical limit for the conventional semicon-ductor devices. Quantum effect becomes prominent in these devices, which degraded the performance of the conventional semiconductor devices. According to quantum effect, tunneling current is created through the gate and the leakage current is dramatically large. To overcome this problem, high?materials were developed to replace the conven-tional gate material,SiO2.From another viewpoint, quantum computer was studied to process information by utilizing the quantum effect of particles. Qubit is the fundamen-tal component of a quantum computer. A qubit can be made of a single electron, or one particle in two energy levels, etc. Among them, quantum dots, which are taken as artifi-cial atoms, are candidates to fabricate qubits, and attracted research interests. Besides, quantum dots have many important application in other fields, such optoelectronics, etc. On the other hand, the demand on memory is surging. Non-volatile memory is very important, for the information stored in non-volatile memories was not lost, after the power was switched off. Not only the important information was safe under accidental power cut, but also the energy consumption can be reduced. Thus non-volatile memory is a hot topic in research field. In this thesis, from these two aspects, the growth of Si based quantum dots/quantum rings and the growth and physical properties of functional Mn oxide films were studied.In-situ annealing at a high temperature of 640?was performed for a low tempera-ture grown Si capping layer, which was grown at 300?on SiGe self-assembled quantum dots with a thickness of 50 nm. Square nanopits, with a depth of about 8 nm and bound-aries along (110), are formed in the Si capping layer after annealing. Cross-sectional 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?. 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?. A subsequent growth of Ge on the nanopit-patterned surface results in the formation of SiGe quantum dot molecules around the nanopits.The size uniformity of self-assembled SiGe quantum rings, which are formed by capping SiGe quantum dots with a thin Si layer, is found to be greatly influenced by the growth temperature and the areal density of SiGe quantum dots. Higher growth temperature benefits the size uniformity of quantum dots, but results in low Ge concen- tration as well as asymmetric Ge distribution in the dots, which induces the subsequently formed quantum rings to be asymmetric in shape, even broken somewhere in the ridge of rings. Low growth temperature degrades the size uniformity of quantum dots, and thus that of quantum rings. A high areal density results in the expansion and coalescence of neighboring quantum dots to form a chain, rather than quantum rings. Uniform quantum rings with a size dispersion of 4.6% and an areal density of 7.8×108cm-2 are obtained at the optimized growth temperature of 640?.An easy approach to fabricate ordered pattern using nanosphere lithography and reactive iron etching technology was demonstrated. Long-range ordered GeSi nanorings with 430 nm period were grown on patterned Si (001) substrates by molecular beam epitaxy. The size and shape of rings were closely associated with the size of capped GeSi quantum dots and the Si capping processes. Statistical analysis on the lateral size distribution shows that the high growth temperature and the long-time annealing can improve the uniformity of nanorings.?-MnO2 films were grown on Si (100) by molecular beam epitaxy and the structures were characterized by AFM, XRD, TEM, etc. It is found that the Er-alloying remarkably improves the thermal stability of?-MnO2 films. When Er concentration is 6%?the films consist of highly oriented?-MnO2 crystal grains.The electric and magnetic properties of?-MnO2 films were studied. Memory effects with different mechanisms were observed for the as-grown films and annealed films. For the as-grown films, the memory effect is caused by charge trapping at the interface:for the annealed films, the memory effect is caused by the ferroelectricity of?-MnO2. The fcrromagnetisrn of as-grown films at low temperature is originated from the moment of Er sublattice. After annealing, ferromagnetic transition occurs near 40K. The ferromag-netism may be caused by the exchange between Er3+ and Mn4+. Near 50K, magnetic vortices are generated when applying magnetic field in the film plane, which results in small coercive force and small residual magnetic moment. By measuring magnetic hysteresis loops in different configuration, the axis along with the growth direction is hard axis and there exists easy axis in the film plane. Therefore, the [100] and [010] of?-MnO2 crystal are hard axes and [001] is the easy axis.