High-density formation of Ge quantum dots on SiO 2

Abstract

We formed high-density Ge quantum dots (QDs) on an ultrathin SiO 2 layer by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) with a germane gas (GeH 4) assisted by a remote plasma of pure H 2. 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 × 10 11 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 GeH 4 by a supply of hydrogen radicals and the dehydration reaction of surface OH bonds plays a role in nucleation of Ge-QDs on SiO 2. 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.