Effect of strain on Si/Si1−xGex valence band structure studied by angle-resolved magnetotunneling spectroscopy

Abstract

We have studied the effect of strain and strain relaxation on the band structure of Si1−xGex quantum wells. Two differently strained, molecular‐beam epitaxy grown Si/Si1−xGex hole resonant tunneling structures were studied: one fully pseudomorphic structure, with the strain in the Si1−xGex well, and the other grown on a thick relaxed Si1−xGex buffer, with the strain in the Si barriers. For the latter structure transmission electron microscopy revealed a large threading dislocation density emanating from the buffer. Using angle‐resolved magnetotunneling spectroscopy we found an anisotropy in the hole states in different in‐plane 90° directions, that was not present in fully pseudomorphically grown structures. We suggest that this is due to anisotropic strain relaxation in the buffer layer.