Preparation And Annealing Characteristics Of The Silicon-germanium Quantum Dots

In this thesis, the fabrication and properties of silicon based germanium quantum dots were studied. The Ge quantum dot was fabricated on pattern substrates, the influence of pattern conditions and growth parameters were investigated. The annealing effect of quantum dot was discussed in the thesis, and the energy level structure of quantum dot was also investigated by photocurrent spectra measurements.The fabrication and morphology of quantum dot on pattern substrate were investigated. Two different approaches were employed in the fabrication of pattern substrates, which were EBL and polystyrene (PS) spheres self assembling, with wet etching and RIE treatment. After MBE growth, a novel circularly arranged structure of Ge quantum dots had been fabricated. It was observed that both pattern and growth parameters affected the morphology of the quantum dots. For example, the circularly organized quantum dot nanostructures cannot be obtained on neither un-patterned substrate nor pattern substrate without oxidation; more deposition of Ge amount caused disappear of circularly structure and dish like structures were former; buffer layers influenced the morphology of quantum dot. These could be all explained by strain induced quantum dot fabrication. The defects related quantum dot arrangements were also shown in this thesis.The annealing effect of quantum dot was discussed in this thesis. The enhancement of photocurrent response was only observed in quantum dot after annealing. Meanwhile, the photo response was decreased when the annealing temperature exceed 800℃. There were three main effects during annealing process: defects elimination, inter diffusion and strain relaxation. The blue shift of photo response could be explained by broaden of band gap, which were arisen from inter diffusion and strain relaxation. Energy levers in the quantum dot were also investigated in this thesis. At least two energy levels were observed in our experiments, and the energy difference between ground state and valance band was about 0.347eV, and the excited state is about 48meV.