Effect of the Ge mole fraction on the formation of a conduction path in cylindrical strained-silicon-on-SiGe MOSFETs

Using two-dimensional simulation, we have demonstrated the effect of the strain or Ge mole fraction xx in a Si1−xGex pillar on the conduction path in cylindrical strained-silicon (s-Si) MOSFETs. We show that for low values of the Ge mole fraction xx in a Si1−xGex pillar, the conduction path forms in the middle of the cylindrical SiGe pillar and not in the s-Si layer at the surface. Only for large values of the Ge mole fraction xx in Si1−xGex pillar does the current conduction path form in the s-Si layer, enabling the advantage of the mobility enhancement of carriers in the device operation. On the basis of our simulation study, we provide the minimum amount of strain or Ge mole fraction xx in a Si1−xGex pillar necessary in a device for the current to flow through the s-Si layer.