Self-oreanized Growth Of Ordered Ge/Si Quantum Dot Array Using Ion Beam Sputtering Deposition Technique

Ge/Si quantum dots (QDs) have a wide range of potential applications in the field of optoelectronics, microelectronics, and single electron device due to its unique quantum confinement effect. It is the key point to realize these applications by controlling nucleation sites accurately and improving the uniformity of QDs size. The ordered QDs grown on template can achieve these aims and become one of the hot topics.In this thesis, ion beam sputtering deposition (IBSD) technique is used to investigate the growth of the ordered Ge QDs on Si substrate, based on polystyrene (PS) nanospheres template and etching technique. The examination results of scanning electron microscope (SEM), atomic force microscope (AFM), and Raman spectrum can be concluded as follow:1. The quality of the monolayer PS nanospheres thin film depends on the dose of the surfactant. The close-packed hexagonal structure can be obtained with suitable dose of the surfactant. When a small dose of surfactant (sodium dodecyl sulfate (SDS)) is dropped into the monolayer PS nanospheres thin film, the surface of this film becomes flat. No obvious defects are observed in this film, that is, the PS nanospheres are ordered arrangement within a monolayer layer. However, this film exhibits double layer structure and orderless arrangement when a large dose of SDS is used.In addition, there are many defects in the PS nanospheres thin film when the SDS is absent.2. The Si or Ge atoms were deposited directly on the monolayer PS nanospheres film with hexagonal close-packed structure, which was arranged on Si substrate, by IBSD. Subsequently, the PS nanospheres are removed during the ultrasonic processing. Then, the annealing treatment is carried out to enhance the crystallinity of the QDs and obtain a larger-area periodic hexagonal QDs array. Compared with the size of QDs grown at different coverage, it was obviously that the base of QDs increased and the height of QDs decreased with coverage enhanced. This can be ascribed to the fact that the additional atoms tend to diffuse to the bottom of the QDs and fill the interspace of the neighbor PS nanospheres.3. A densely ordered pit pattern was prepared on Si substrate via nanosphere lithography (NSL). Then, an array of Ge QDs grew on this pit-patterned Si substrate by IBSD. The diffusion and gather of Ge adatoms on patterned substrate have been studied at different growth temperature, buffer thickness and ramping temperature of Ge. And these conditions were used to modulate the minimal point of surface potential. After controlled the minimum of surface potential on patterned substrate, the hexagonal distributed and size uniformity Ge quantum dots were arrayed periodically within and outside the pits respectively, at suitable surface curvature and diffusion condition. The mechanism of Ge QDs nucleated on patterned substrate was analyzed. The results suggest that the effect of surface energy and strain energy on the surface chemical potential controls the nucleation site of the Ge QDs.