We have studied the impact of the hole shape on the growth of Ge dots. Si substrates that have been templated by means of electron beam lithography and reactive ion etching have been used to grow Si buffer layers at different substrate temperatures by molecular-beam epitaxy. Atomic-force-microscopy studies show that for high substrate temperatures, the prepatterned holes are smeared out. A model has been employed to quantitatively analyze the smearing out of the holes. The study further shows that the shape of the holes has a substantial impact on the morphology of the subsequently grown Ge dots, i.e. Ge dots grown in smeared out holes show a tendency towards an inhomogeneous size distribution and the formation of multiple dots in one hole.
We studied the impact of weak photon flux on the electron transport in strongly localized quantum dot system. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. This phenomenon has the potential to detect a single photoexcited carrier for a wide range of wavelength. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photoinduced fluctuations on the light intensity and the steplike response of conductance on the pulse excitation.
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