EFFECT OF STRAIN ON SI/SI1-XGEX VALENCE BAND-STRUCTURE STUDIED BY ANGLE-RESOLVED MAGNETOTUNNELING SPECTROSCOPY

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 state in different in-plane 90-degrees directions, that was not present in fully pseudomorphically grown structures. We suggest that this is due to anisotropic strain relaxation in the buffer layer.