Investigation On High Quality Ge Quantum Dots Preparated By Ion Beam Sputtering

When the Ge quantum dot size is less than or close to the exciton Bohr radius (24.3 nm), Ge quantum dots make a series of quantum effects, such as quantum confinement effect, quantum tunneling penetration effect and nonlinear optical effect. The photoelectric performance of the material is different from that of the bulk material, and it can be widely used in the detector, laser and other optoelectronic devices. Furthermore, one of the major advantages of Ge is its compatibility with conventional Si integrated circuit technology, so Ge quantum dots have become one of the hot spots in optoelectronics and microelectronics. In this thesis, we use the ion beam sputtering technique to grow the high quality Ge quantum dots, hoping that the Ge quantum dots with high crystallinity and high uniformity are obtained by optimizing the experimental parameters.High quality Ge quantum dots was successfully grown by ion beam sputtering are studied. First, The growth and evolution of Ge quantum dots were researched by controlling the growth temperature of Si buffer layer and deposition thickness of Ge layer. The experiments show that c-Ge-Ge vibrational peaks will be observed at 298 cm-1 when the Si buffer layer is grown at 800℃, which is transverse optical vibration peak of crystal Ge. On the basis of this, the deposition thickness of Ge is controlled. When the thickness of the deposition of Ge is 2.5 nm, the density of Ge quantum dots is the largest and the size is smallest. Then, the crystallinity and uniformity of Ge quantum dots are studied, it is found that the crystallinity of Ge and Si are 43% and64%, respectively. The standard deviation of the height and width of the Ge quantum dots are 3.53 and 10.71 nm, the uniformity of the spatial distribution is 58.8% at the growth temperature of Si buffer layer about 700 ℃. However, when the growth temperature is increased to 800℃,the crystallinity of Ge and of Si are 66% and 89%, the standard deviation of the height and width of the Ge quantum dots are 2.49 and 7.37 nm, and the uniformity of the spatial distribution is 64.56%.. It shows that the crystallinity and uniformity of Ge quantum dots are improved when the growth temperature of Si buffer layer is higher.And furthermore the growth mode of Si buffer layer changed, and the interval growth of the buffer layer is adopted at different temperature. The interval growth of Si buffer layer at 800℃the Si buffer layer has no amorphous wave packet, so it can improve the crystallinity of the Si buffer layer.. After changing the number of interval growth, it find that the Ge quantum dot density increased at a standstill for the 3 time., and the growth of Ge layer makes the crystallization of Si buffer layer increase.Finally, the annealing process is helpful to change the crystallinity and uniformity of Ge quantum dots. The Si buffer layer is annealed at different time, it is found that the crystallinity of Si and Ge increased to 71% and 94% with increasing of annealing time, so the increase of the annealing time of Si is beneficial to the crystallization of Si and Ge. After the study of the Ge layer situ annealing at different time, it manifests that, with the increase of the annealing time of Ge, the standard deviation of the Ge quantum dot size is gradually reduced, the uniformity increases to 91.89% and the crystallinity of Ge becomes 88%, which indicates that the increase of the annealing time of Ge layer can improve the uniformity of Ge quantum dots, and the crystallinity is also better. After the study of post annealing effect, it is found that the crystallinity of the Si buffer layer was increased, and the morphology of the quantum dots is found to have been greatly changed by Raman spectroscopy, A number of nano-hole structures have emerged on the surface of the sample, which is attributed to the diffusion and depletion of the atoms in the Ge quantum dots.