A self-ordered, body-centered tetragonal superlattice of SiGe nanodot growth by reduced pressure CVD

Abstract

Self-ordered three-dimensional body-centered tetragonal (BCT) SiGe nanodot structures are fabricated by depositing SiGe/Si superlattice layer stacks using reduced pressure chemical vapor deposition. For high enough Ge content in the island (>30%) and deposition temperature of the Si spacer layers (T > 700 °C), we observe the formation of an ordered array with islands arranged in staggered position in adjacent layers. The in plane periodicity of the islands can be selected by a suitable choice of the annealing temperature before the Si spacer layer growth and of the SiGe dot volume, while only a weak influence of the Ge concentration is observed. Phase-field simulations are used to clarify the driving force determining the observed BCT ordering, shedding light on the competition between heteroepitaxial strain and surface-energy minimization in the presence of a non-negligible surface roughness.

Capillary-driven elastic attraction between quantum dots

“…The technique best suited for device integration is epitaxy where quantum dots growth is driven by the elastic relaxation of the misfit strain. Even-though its general picture is rather well documented and understood 33 , some puzzling experimental outcomes can still be revealed by careful scrutiny [34][35][36][37] . One such experimental finding is the clustering of Ge quantum dots in their early stage of growth on Si 38 .…”

Self-Ordered Ge Nanodot Fabrication by Using Reduced Pressure Chemical Vapor Deposition

“…Ge nanodot formation on concave part) is due to surface energy reduction and dot-on-dot vertical alignment is caused by strain energy reduction. In the case of 3D SiGe nanodot formation on a rough Si surface, 10,11 the preferred position of the SiGe nanodot formation is in concave regions, because tensile strain above the embedded SiGe nanodots is not high enough. As a result, the main driving force of the SiGe nanodot formation is not strain energy reduction but surface energy reduction.…”

“…By repeating several cycles of the Si 0.6 Ge 0.4 and Si layer deposition, a BCT Si 0.6 Ge 0.4 nanodot layer stack with checkerboard mesa structured Si surface is formed because the Si 0.6 Ge 0.4 nanodot formation occurs at concave region of the Si surface during temperature ramping up to Si spacer growth temperature. 10 The periodicity of the checkerboard structure in [110] direction is ∼150 nm. Root mean square (RMS) roughness and height of the Si mesas are 1.2 nm and ∼4 nm, respectively.…”

“…8,9. In a previous study, we reported a self-ordered body-centered tetragonal (BCT) SiGe nanodot formation using reduced pressure (RP) chemical vapor deposition (CVD) by repeating SiGe and Si layer stack deposition. 10 By repeating several cycles of the SiGe and Si layer stack deposition using SiH 4 as precursor for the Si layer, checkerboard Si mesas are formed on embedded SiGe dots and next SiGe dots are formed in concave region between the Si mesas. By using SiH 2 Cl 2 as precursor for the Si growth, a vertically aligned dot-on-dot structure was formed because of smooth Si spacer surface formation.…”

Three-Dimensional Self-Ordered Multilayered Ge Nanodots on SiGe

“…[21][22][23] In our previous work, laterally and vertically self-aligned multilayered SiGe nanodots fabrication with Si spacer on Si(001) were studied. 24,25 Vertical and body-centeredtetragonal alignment were obtained by controlling local distribution and surface energy. In this study, we demonstrate 3-dimensional (3D) self-ordered Ge nanodots on SiGe virtual substrate (VS) by SiGe/Ge cyclic epitaxial growth and discuss the effects of fabrication parameters.…”