One-Dimensional to Three-Dimensional Ripple-to-Dome Transition for SiGe on Vicinal Si (1 1 10)

Abstract

SiGe heteroepitaxy on vicinal Si (1 1 10) is studied as a model system for one-dimensional (1D) to three-dimensional growth mode transitions. By in situ scanning tunneling microscopy it is shown that the 1D-3D transition proceeds smoothly from perfectly facetted 1D nanoripples to coarsened superripples, tadpoles, asymmetric domes, and barns without involving coalescence or agglomeration. By extension of the studies to a wide range of SiGe compositions, a 1D-3D growth phase diagram is obtained. Total energy calculations reveal that the observed critical transition volumes are fully consistent with thermodynamic driven strain relaxation.

Formation of Self-Connected Si0.8Ge0.2 Lateral Nanowires and Pyramids on Rib-Patterned Si(1 1 10) Substrate

“…Thus, due to the rather low growth rate and medium growth temperature used in our work, it can be expected that the nanowires and the pyramids form simultaneously on both facets. Further geometry evolution for the Si-rich SiGe on flat Si(1 1 10) substrate has also been elaborated in previous work [27, 41]. But in this work, the rib-patterning along the [1 −1 0] direction induces the truncating for nanowires at the rib shoulders.…”

“…It is well resolved that most of the nanowires on the rib top are terminated with two intersecting {105} facets [27]. Moreover, a self-connecting phenomenon at the rib shoulder between the nanowires on rib-top and the pyramids on the (0 0 1) faceted sidewall has been observed as highlighted with dashed circles in Fig.…”

“…Figure 3c is the top view of the schematic where the two smoothly self-connected {105} facets of extended nanowires are marked with shadows to indicate the final surface morphology. While the coexistence of SiGe huts with the pyramids on both flat Si (001) and Si (1 1 10) substrates has been observed and studied systematically [26, 27], the self-connecting of the nanowires with the pyramids at the rib shoulder between the (1 1 10) rib-top and the (0 0 1) faceted sidewall has not been reported yet. Many huts can be observed sitting on the faceted sidewalls at various sites in the AFM images as highlighted by square dashes shown in Fig.…”

“…The total energy density difference exhibited above is quite small. Nevertheless, this is not uncommon that a small total energy difference in the order of 1% may lead to the onset of the energetically preferential geometry [19, 27], so long as the quasi equilibrium growth condition is fulfilled. The rather low deposition rate of 0.12 Å/s and medium temperature of 650 °C during our MBE growth exactly provide the favorite condition which enabled the thermodynamics the dominating driven force for the observed phenomena.…”

“…So far, template patterning is one of the most successful routes to achieve controllable growth of the lateral SiGe nanowires on both miscut [19] and singular Si (001) substrate [26]. Recent work has also showed the morphology evolution between the nanowires and the islands during the variation of the growth temperature and the thickness of the Si spacer [27, 28]. Nevertheless, there has been very few reports on the evolution of the SiGe lateral nanowires on the patterned miscut substrate, where the coexistence of the nanowires and islands are inevitable.…”