RAMAN INVESTIGATIONS OF ELASTIC STRAIN RELIEF IN SI1-XGEX LAYERS ON PATTERNED SILICON SUBSTRATE

The appearance of an elastic strain relief in narrow mesalike patterned Si1-xGex heteroepitaxial layers is shown. A Si1-xGex layer was deposited on a mesalike patterned Si(001) substrate by molecular-beam epitaxy. The germanium concentration was x=14%, the layer thickness h=96 mum was several times larger than the critical thickness h(c). The layers on top of the mesas were investigated by Raman microscopy. The Raman line shifts of the wider mesas and their dislocation densities agree with the predicted strain reduction by generation of misfit dislocations. On the narrow mesas an additional shift of the Raman lines toward the unstrained alloylike Raman frequency was measured. It is caused by an elastic strain relief on top of the narrow mesas. An estimation of the expected Raman line shifts is given assuming an uniaxially strained SiGe layer. The calculated line shifts agree sufficiently with the measured values. The elastic strain relief reduces the free energy of the layer-substrate system, reduces the stress in the pseudomorphic layer, and stabilizes the structure. The effect arises if the mesas are narrower than 2 mum. It is therefore of interest in all submicrometer technologies.