Morphology and photoluminescence of ultrasmall size of Ge quantum dots directly grown on Si(0Â 0Â 1) substrate

► Sub-10-nm domelike Ge QDs with uniform size were obtained directly on the Si(0 0 1) surface. ► Their density is the highest one among the Ge QDs grown directly on Si surface. ► Two metastate QDs, pyramid-to-dome and multiheaded dome, were observed due to no post-annealing. ► The QDs own a very strong non-phonon peak with a large blue shift of 0.19 eV at 14 K.