Islanding, growth mode and ordering in Si heteroepitaxy on Ge(001) substrates structured by thermal annealing

TL;DR

This study investigates how thermal annealing of nanostructured Ge substrates influences Si/Ge heteroepitaxial growth modes, islanding behavior, and spatial ordering, revealing substrate structure-dependent growth dynamics and site patterning.

Contribution

It demonstrates how substrate misorientation and surface structure control growth modes, islanding critical thickness, and dot site ordering in Si heteroepitaxy on Ge(001).

Findings

Lowered islanding critical thickness on highly-miscut Ge(001).

Growth mode varies with surface domain structure.

Substrate patterning influences dot site spatial correlation.

Abstract

Si/Ge heteroepitaxial dots under tensile strain are grown on nanostructured Ge substrates produced by high-temperature flash heating exploiting the spontaneous faceting of the Ge(001) surface close to the onset of surface melting. A very diverse growth mode is obtained depending on the specific atomic structure and step density of nearby surface domains with different vicinal crystallographic orientations. On highly-miscut areas of the Ge(001) substrate, the critical thickness for islanding is lowered to about 5 ML, in contrast to the 11 ML reported for the flat Ge(001) surface, while on unreconstructed (1x1) domains the growth is Volmer-Weber driven. An explanation is proposed considering the diverse relative contributions of step and surface energies on misoriented substrates. In addition, we show that the bottom-up pattern of the substrate naturally formed by thermal annealing determines a spatial correlation for the dot sites.