High-density formation of Ge quantum dots on SiO2

We formed high-density Ge quantum dots (QDs) on an ultrathin SiO2 layer by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) with a germane gas (GeH4) assisted by a remote plasma of pure H2. We then characterized the electronic charged states of the QDs by an AFM/Kelvin probe technique. The formation of single crystalline Ge-QDs with an areal dot density of ∼2.0 × 1011 cm−2 was confirmed after examining the surface morphology and lattice by atomic force microscopy and transmission electron microscopy, respectively. It has been suggested that an increase in the flux of deposition precursors due to efficient decomposition of GeH4 by a supply of hydrogen radicals and the dehydration reaction of surface OH bonds plays a role in nucleation of Ge-QDs on SiO2. Surface passivation with hydrogen may also promote the surface migration of deposition precursors during LPCVD. The surface potential of the dots changed in a stepwise manner with respect to the tip bias due to multistep electron injection into and extraction from the Ge-QDs.

Research highlights
► We formed high-density Ge-QDs on an ultrathin SiO2 layer by controlling the early stages of LPCVD with GeH4 assisted by a remote H2 plasma.
► Hydrogen radicals play roles in both creation of nucleation sites on OH-terminated SiO2 surfaces and in decomposition of GeH4 to generate the precursors of Ge-QDs.
► The surface potential of the dots changed in a stepwise manner with respect to the tip bias due to multistep electron injection into and extraction from the Ge-QDs.
► These results provide useful information for the fabrication of multi-valued floating gate memories.