Mechanism of crack formation in strained SiGe(111) layers

Strained SiGe layers are grown on Ge(1 1 1) and Ge-on-Si(1 1 1) substrates with and without forming mesapatterning, where the Ge and Ge-on-Si(1 1 1) outside of the defined mesa-pattern area are etched down by various thicknesses. We find that high-density cracks are formed both inside and outside of the mesa-area and the cracks are connected across the mesa-boundary when the Ge layer partially remains outside of the mesa area (partially etched case). By contrast, the crack formation is completely suppressed when the Ge is fully etched, leaving the Si on the etched surface. These results mean that the cracks are initially generated in the SiGe layer grown on the Ge outside of the mesa-area and they propagate into the mesa-area, making the mesa-area covered with crack networks. In addition, since it is implied that the density of the crack generation sources is not high, the crack-free SiGe can be grown in the mesa area by fully removing the Ge layer outside of the mesa area. Therefore, the patterning method can provide very attractive templates highly applicable to strained SiGe-based optoelectronic and spintronic devices with superior performances.