Abstract
In this tutorial we review recent progress in the design and growth of epitaxial semiconductor nanostructures in lattice-mismatched material systems. We focus on the Ge on Si model system after pointing out the similarities to III-V and other growth systems qualitatively as well as quantitatively. During material deposition, the first layers of the epitaxial film wet the surface before the formation of strain-driven three-dimensional nanostructures. In particular, we stress that the supersaturation of the wetting layer (WL), whose relevance is often neglected, plays a key role in determining the nucleation and growth of nanodots (NDs), nanodot-molecules and nanowires (NWs). At elevated growth temperatures the Ge reservoir in the planar, supersaturated WL is abruptly consumed and generates NDs with highly homogeneous sizes - a process mainly driven by elastic energy minimization. Furthermore, the careful control of the supersaturated Ge layer allows us to obtain perfectly site-controlled, ordered NDs or ND-molecules on pit-patterned substrates for a broad range of pit-periods. At low growth temperatures subtle interplays between surface energies of dominant crystal facets in the system drive the material transfer from the supersaturated WL into the elongating NWs growing horizontally, dislocation- and catalyst-free on the substrate surface. Due to the similarities in the formation of nanostructures in different epitaxial semiconductor systems we expect that the observation of the novel growth phenomena described in this Tutorial Review for Ge/Si should be relevant for other lattice-mismatched heterostructure systems, too.
Highlights
quantum dots (QDs) lasers, based on In(Ga)As/GaAs QDs, have shown superior performance over conventional quantum well lasers.[1,2] Single photon and entangled photon-pair emission were demonstrated using single InAs/GaAs QDs,[3,4,5] making26 | Chem
We have reviewed the recent progress in epitaxial growth of semiconductor nanostructures, focusing on the Ge/Si model system
We have shown that the metastable or supersaturated Ge wetting layer (WL) plays a key role in determining the nucleation and growth of NDs and NWs
Summary
QD lasers, based on In(Ga)As/GaAs QDs, have shown superior performance over conventional quantum well lasers.[1,2] Single photon and entangled photon-pair emission were demonstrated using single InAs/GaAs QDs,[3,4,5] making. Ge and SiGe NDs on Si have been used as buried stressors to enhance carrier mobility in Si channels,[6,7] as effective phononscattering centers to reduce thermal conductivity[8] and as single-hole supercurrent transistors.[9] All these advancements and breakthroughs would not have been possible without the development of self-organized growth of nanostructures. Dr Martyna Grydlik conducted her PhD studies at the Institute of Semiconductor and Solid State Physics and received her PhD degree in Physics in 2011 from the Johannes Kepler University, Linz, Austria, supervised by Dr. Gunther Bauer. His interests include interdisciplinary research fields, ranging from low-dimensional electronic materials to energy storage and microrobotics. We emphasize the importance of controlling the thickness of deposited thin-films on a sub-ångstrom (o0.01 nm) level in order to obtain highly uniform NDs (Section 4.1), ordered NDs with arbitrary inter-ND spacing (Section 4.2), several micrometer long Ge nanowires (Section 4.3) and nanowire bundles (Section 4.4)
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