The influence of boron segregation and silicon cap-layer thickness on two-dimensional hole gases ͑2-DHGs͒ has been investigated in Si/Si 0.8 Ge 0.2 /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.
Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2 X 102' cm -3, to elucidate profile control and electrical activation over the growth temperature range 450-900 "C. Precipitation and surface segregation effects were observed at doping levels of 2 X 102' cm -3 for growth temperatures above 600 "C. At growth temperatures below 600 "C, excellent profile control was achieved with complete electrical activation at concentrations of 2 x 102' cm -3, corresponding to the optimal MBE growth conditions for a range of Si/Si,Gel --x heterostructures.
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