Issues on the molecular-beam epitaxial growth of p -SiGe inverted-modulation-doped structures

The influence of boron segregation and silicon cap-layer thickness on two-dimensional hole gases (2-DHGs) has been investigated in Si/Si0.8Ge0.2/Si inverted-modulation-doped heterostructures grown by solid-source molecular-beam epitaxy. Boron segregation, which is significant in structures with small spacer layers, can be suppressed by growth interruption after the boron doping. How growth interruption affected the electrical properties of the 2-DHG and the boron doping profile as measured by secondary ion mass spectroscopy are reported. We report also on the role played by the unpassivated silicon cap, and compare carrier transport at the normal and inverted interfaces.