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

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.

11 pages, 7 figures