Nanosecond laser induce size-controllable SiGe islands with high Ge composition, large aspect ratio and defect-free characteristics

•Single crystalline SiGe islands can be directly formed by pulse laser-dewetting amorphous germanium thin films.•By changing the laser fluence, the size of these SiGe islands, can controlled from 40 to 150nm.•The surface mean height has the same variation tendency with the mean diameter, which result in the high aspect ratio islands (1.06).