Determination of local lattice tilt in Si1−xGex virtual substrate using high resolution channeling contrast microscopy

Strain relaxed Si1−xGex virtual substrates with low densities of threading dislocations are grown by molecular beam epitaxy or chemical vapour deposition using the compositional grading technique. They have a wide range of applications in microelectronic and optoelectronic devices. A common surface feature of such virtual substrates is a cross-hatch pattern that is oriented along orthogonal [1 1 0] directions and is believed to be associated with strain relaxation processes. Such cross-hatch roughening affects carrier mobility and the quality of the subsequent layers grown on the virtual substrates. Accurate measurements of the material properties of these virtual substrates are essential for the optimization of the growth processes and conditions. Channeling contrast microscopy, which uses a focused ion beam to obtain laterally resolved channeling yield information, is an ideal technique to determine the microstructural characteristics of such samples. Here, we determine the extent of the local lattice tilt from channeling contrast measurements and investigate the influence of the growth temperature and grading rate on surface morphology, crystalline quality and the extent of the lattice tilts in the constant composition layer.