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Abstract

We present a detailed, investigation of novel strain-driven
semiconductor nanostructures. Our examinations include self-
assembled nanoholes, lateral quantum-dot (QD) molecules, and
rolled-up nanotubes. We overgrow InAs QDs with GaAs and apply
atomically precise in situ etching to fabricate homogeneous
arrays of nanometer-sized holes with diameters of 40 to 60 nm
and depths up to 6.2 nm. The structural properties of the
nanoholes can be precisely tuned by changing the QD capping
thickness and the in situ etching time. We show that strain
fields surrounding the buried quantum dots drive the nanohole
formation process. We overgrow the mmoholes with 0.2- to 2.5-ML
InAs and observe the formation of compact lateral InAs QD
molecules. The number of QDs involved in a lateral QD molecule
can be tuned from two to six by changing the growth
temperature. Our systematic photoluminescence study documents
the QD molecule formation process step by step and helps to
interpret our structural results. We also present the
fabrication of laterally aligned lateral QD bimolecules by
growing InGaAs on a GaAs (001) substrate patterned with a
square array of nanometer sized holes. Charge carriers in such
bimolecules might serve as quantum gates in a future
semiconductor based quantum computer. Furthermore, we release
strained semiconductor bilayers from their surface to fabricate
individual rolled-up semiconductor micro- and nanotubes. We
control the diameter of strain-driven In(Ga)As-GaAs tubes from
the nanometer to micrometer range by simply,changing the layer
thicknesses and built-in strain. We propose to roll in metal
strip lines to fabricate nanocoils and nanotransformers. To
support our proposition, we fabricate homogeneous single and
twin GaInP tubes. We present a straight GaInP microtube of more
than 2 mm in length and a length-to-diameter ratio of about
2000, thus, elucidating the great potential of this technology.