Alloying of self-organized semiconductor 3D islands

Abstract

We present a short review of alloying in uncapped self-organized semiconductor heteronanostructures. Our aim is to provide a logical guide through the main concepts proposed in recent scientific debates. In particular, we focus on the issue of mapping the chemical composition within individual germanium quantum dots grown on silicon surfaces, a widely studied model system with high technological potential. We discuss the different experimental results reported so far in the literature, along with the main theories suggested for their rationalization. In particular, we expand on the interplay of competing factors, including thermodynamic considerations, strain relaxation and kinetic limitations. Finally, we propose a possible pathway towards a unifying picture, with the intention to motivate further research on this topic.

Kinetic Monte Carlo simulations and cross-sectional scanning tunneling microscopy as tools to investigate the heteroepitaxial capping of self-assembled quantum dots

“…The issue of bulk diffusion is somewhat controversial (e.g. Ratto et al 33 ) and while it is easy to include such effects in our KMC model it is difficult to justify the mechanisms that would actually lead to bulk diffusion. For this reason, we have chosen to neglect it, however, as discussed below, this does not mean we ignore intermixing.…”

GeSi intermixing in Ge nanostructures on Si(111): An XAFS versus STM study

“…An intense debate has focused on the main driving forces responsible for alloying, which has been alternatively attributed to segregation 33,34 or to entropic/kinetic 35 or enthalpic factors. 36,37 As a result of such alloying phenomena the effective lattice mismatch is substantially driven below the nominal 4.2%.…”

“…[37][38][39] The emerging picture is that island evolution/ripening and GeSi alloying both lead to a partial strain relief and depend on energetic as well as kinetic fac-tors. These phenomena are associated with significant mass transport during growth and possibly postdeposition annealing.…”

Modeling the plastic relaxation onset in realistic SiGe islands on Si(001)

“…Recently, the closely related behavior of Ge/Si vs III-V compounds was nicely analyzed. 6,7 In-depth experimental analysis of Ge/Si islands revealed a very fascinating physics, in particular for what concerns the morphological evolution during deposition of the 3D structures. It is known that islands grown by molecular-beam epitaxy ͑MBE͒ at common ͑500-800°C͒ temperatures first appear as prepyramids and ͑105͒ pyramids ͑shallower in shape͒, and then as domes and barns ͑steeper morphologies, involving multiple exposed facets͒.…”