Abstract
For the prototypical Ge/Si(001) system, we show that at high growth temperature a new type of Stranski-Krastanow islands is formed with side facets steeper than {111} and high aspect ratio. Nano-goniometric analysis of the island shapes reveals the presence of six new facet groups in addition to those previously found for dome or barn-shaped islands. Due to the highly multi-faceted island shape and high aspect ratio, the new island types are named "cupola" islands and their steepest {12 5 3} side facet is inclined by 68°to the substrate surface. Assessing the relative stability of the new facets from surface area analysis, we find that their stability is similar to that of {113} and {15 3 23} facets of dome islands. The comparison of the different island shapes shows that they form a hierarchical class of geometrical structures, in which the lower aspect ratio islands of barns, domes and pyramids are directly derived from the cupola islands by successive truncation of the pedestal bases without facet rearrangements. The results underline the key role of surface faceting in the process of island formation, which is as crucial for understanding the island's growth evolution as it is important for device applications.
Highlights
SiGe islands grown on Si(001) substrates exhibit a large variety of shapes that strongly depend on the Ge growth temperature and the thermal energy provided to the system [1]
The islands are significantly larger than the barns and domes obtained at lower TGe, where for 700°C typical values of 20 and 120 nm for height and diameter are found [6] and the density of approximately 109 cm-2 is about a factor of 50 higher than that found for TGe = 900°C
The higher growth temperature results in a higher degree of Si/Ge intermixing, as estimated from the ratio of 5 ML Ge incorporated in the dots (8 ML minus 3 ML assumed to be in the wetting layer) over the total island volumes measured by atomic force microscopy (AFM)
Summary
SiGe islands grown on Si(001) substrates exhibit a large variety of shapes that strongly depend on the Ge growth temperature and the thermal energy provided to the system [1]. The dotted and dashed circles indicate the surfaces with inclination of θ = 25.2° and 54.7°, which include the prominent {113} and {111} facets observed for dome and barn islands, respectively.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
