Shape evolution of MBE grown Si$_{1-x}$Ge$_{x}$ structures on high index Si(5 5 12) surfaces: A temperature dependent study

TL;DR

This study investigates how growth temperature and heating methods influence the shape, size, and composition of Ge-Si islands on Si(5 5 12) surfaces during molecular beam epitaxy, revealing temperature-dependent morphological transitions.

Contribution

It provides new insights into temperature and heating method effects on SiGe island morphology and composition on high index Si surfaces during MBE growth.

Findings

Spherical islands at 600°C with bimodal distribution in radiative heating.

Faceted structures emerge at 700°C in radiative heating.

Aligned trapezoidal SiGe structures form at 600°C with DC heating.

Abstract

The morphological evolution and the effect of growth temperature on size, orientation and composition of molecular beam epitaxy grown Ge-Si islands on Si(5 5 12) surfaces have been investigated in the temperature range from room temperature (RT) to 800$^\circ$C. Two modes of substrate heating i.e. radiative heating (RH) and direct current heating (DH) have been used. The post-growth characterization was carried out ex situ by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (X-TEM) and Rutherford backscattering spectrometry (RBS). In the RH case, we found spherical island structures at 600$^\circ$C with a bimodal distribution and upon increasing temperature, the structures got faceted at 700$^\circ$C. At 800$^\circ$C thick ($\sim$ 122nm) dome like structures are formed bounded by facets. While in the case of DC heating, after the optimum critical temperature 600$^\circ$C, well aligned trapezoidal Si$_{1-x}$Ge$_x$ structures with a graded composition starts forming along the step edges. Interestingly, these aligned structures have been found only around 600$^\circ$C, neither at low temperature nor at higher temperatures.