Sputtering Growths And Optical Properties Of Ge Quantum Dots And Films On Si Substrates

Crystal Ge (c-Ge) materials, such as, Ge/Si quantum dots (QDs) and Ge thin films, have always been a research hotspots in Si-based optoelectronics and microelectronics in the past decades owing to their compatibilities with Si technology and excellent properties compared with Si.We investigate the photoluminescence, near-and mid-infrared absorptions of mutilayer Ge/Si QDs prepared by Ion Beam Sputtering Deposition (IBSD) using the optimal growth parameter of Ge/Si QDs in our previous works. Two absorption peaks are obseved at 1.5 and 3.4 μm, which correspond to the interband transition and the transition of the bound to continuous state, respectively. Furthermore, their corresponding energies are good agreement with their energy level alignments. Unfortunitely, the strengths of their absorptions are very weak and even the result is unrepeatable, which are attributed to the low-quality of Ge QDs grown on a mixed-phase Si buffer or spacer with amorphous and crystalline. However, it is demonstrated that the high-quality Ge QDs can be prepared by the method of the interval-growth Si layer owing to improving the crystallinity of Si layer.Considering the fact that Ge/Si films photodectors display a high responsivity, we carry out the research of the low-temperature (LT) and high-temperature (HT) two-steps Ge films grown on Si substrates by DC magnetron sputtering. It is observed that the two-step Ge films don’t achieve the epitaxial growth but show the random growth in our experiments. What’s more, the root-mean-square (RMS) surface roughnesses of Ge films decrease with increasing growth temperature of LT Ge layer, which ascribes to the effect of annealing on the surface morphology of LT Ge layer. More importantly, the two-step Ge films display the obvious absorptions at 1.0～1.8 μm.Additionally, we also investigate the microstructure and optical properties of Ge films on Si substrates prepared at low temperatures by DC magnetron sputtering and the effect of in situ annealing on them. With increasing growth temperature, Ge films undergo a transition from amorphous to microcrystalline, then to polycrystalline. After annealing, these thin films transform into polycrystalline films with the (111) preferred orientation and identical crystal sizes. The surfaces of the amorphous and microcrystalline Ge films are severely coarsened, while the polycrystalline Ge film still displays a smooth surface. The growth mechanisms of Ge films with different crystalline phases in the annealing process are discussed, which can better explain their morphology evolutions. Their infrared absorptions at 1.0-1.8 μm are enhanced after the annealing treatment.