An investigation on the thermal stability of the Ge xSi 1-x⧸Si superlattice grown by MBE

Abstract

Strained Ge x Si 1- x /Si superlattices with Ge content of 0.48 and 0.49 grown by MBE at 420°C (sample A) and 570°C (sample B) were annealed and studied by X-ray diffraction, Raman scattering and TEM. The cross section TEM image of the samples before annealing showed that the growth of sample A was two-dimensional, but for sample B, the growth of the Ge x Si 1- x layer was three-dimensional. By the X-ray diffraction spectra before and after annealing for samples A and B, the strain relaxations from X-ray diffraction measurements were 27% and 35% for samples A and B, respectively. This difference might be from the three-dimensional growth of sample B, in which the strain was stronger than that in sample A. Raman scattering measurements showed that the Ge-Ge peak and the Ge-Si peak shifted towards the lower energy after annealing, while the Si-Si peak shifted towards the higher energy. The reason for the shift of these peaks could be explained by the common contribution of the strain relaxation and the internal diffusion of Ge atoms into the Si layer. In addition, the behavior of the strained Ge x Si 1- x /Si superlattice annealed by rapid thermal annealing technology was also studied. A sample of superlattice with a Ge content of 0.46 was rapidly thermal annealed at the temperature range of 600 to 1000°C and at each temperature the sample was annealed twice for 40 s each time. From X-ray diffraction measurements it could be found that as the annealing temperature increased from 600 to 900°C, the strain relaxation would increase from 19% up to 57%. As the sample was annealed at 1000°C, no satellite peaks were in the X-ray diffraction spectra and no multilayer structure could be observed in the cross section TEM image, that is, in the sample the GeSi layers were completely mixed up with the Si layers.