Abstract:Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates by solid source molecular beam epitaxy. The surface morphology obtained by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy images (TEM) shows that the Ge islands are preferentially grown at the sidewalls of pure Si stripes along [-110] direction at 650 o C or along the trenches, whereas most of the Ge islands are formed on the top terrace when the patterned stripes are covered by a strained GeSi buffer layer. Reducing the growth temperature to 600 o C results in a nucleation of Ge islands both on the top terrace and at the sidewall of pure Si stripes. A qualitative analysis, based on the growth kinetics, demonstrates that the step structure of the stripes, the external strain field and the local critical wetting layer thickness for the islands formation contribute to the preferential positioning of Ge islands on the stripes.
I. INTRODUCTIONSelf-assembled quantum dots (SAQD) have become an intensive research topic not only because of their promising device applications 1 but also to understand the fundamental process of strained thin film growth. A frequently employed growth mode of a strained heteroepilayer is the so-called Stranski-Krastanow(SK) mode, where after a thin wetting layer the epilayer releases the misfit strain by 3D island formation. These straightforwardly formed islands can be small and in general dislocation-free, but random in position. Although locally laterally ordered SAQD have been observed, i.e., via the growth of a multilayer of SAQD, 2,3 or the growth of SAQD above a buried strained layer with a dislocation network, 4 or growth of SAQD on a vicinal surface with step-bunching, 5,6 these kinds of short-range ordered SAQD are not adequate for most electronic or optoelectronic device applications. 1 Recently, it was shown that the combination of lithographic etching techniques and the SK growth mode provides a potential to grow long-range spatially ordered SAQD. 7-13 Some interesting phenomena have been observed during the growth of SAQD on patterned substrates. For instance InAs SAQD can be preferentially grown either on the top terraces or at the sidewalls or at the trenches of stripe-patterned GaAs substrates. 7 The number of InAs SAQD can be adjusted by the depth of patterned holes. 8 Ge SAQD are preferentially grown at the edges of selectively grown Si mesas in etched SiO 2 windows, 9,10 while they preferentially grow at the sidewalls of pure Si stripes. 11 These phenomena were discussed from the point of view of either energetics or kinetics. However, no detailed discussion about the growth of SAQD on patterned substrates has been presented so far.It is the purpose of this paper to present a description of a growth mechanism to explain the main features of the Ge island formation on stripe-patterned Si (001) substrates. The preferential positioning of Ge SAQD grown at 650 o C on patterned pure Si stripes with different periodicity and height is analyzed from AFM im...