Charge transfer in p +-Si / Si 1-xGe x modulation doped heterostructures grown by RTCVD

Abstract

High-quality Si/Si 1-xGe x simple (both normal and inverted) and double modulation doped heterostructures with 0<x<0.3 have been grown on Si(100) substrates by rapid thermal chemical vapor deposition (RTCVD) at low temperature (610°C), using silane, germane and diborane in a hydrogen carrier gas. Hall measurements have been performed from 300 to 20 K and show the hole confinement in the Si 1-xGe x layer. The dependence of the confined density and hole mobility on germanium concentration and Si spacer thickness is presented. A simple calculation taking into account a single quantized energy level at each Si/SiGe interface has been made and yields confined densities in good agreement with experimental results. Magnetotransport measurements have been performed on several samples, and well defined Shubnikov de Haas oscillations and integral quantum Hall plateaus up to v=32 can be observed at 1.6 K in the magnetic field range 2–13 teslas. These data confirm the existence of a two dimensional hole gas at each Si/SiGe interface, with a density ranging from 3.10 11 to 10 12 cm -2, and a top mobility above 4000 cm 2/Vs, comparable to the best results obtained in similar MBE grown structures. Finally, these results demonstrate that high-quality p-type modulation-doped Si/Si 1-xGe x heterostructures can be grown by RTCVD at low temperature, and illustrate the latter's capabilities in terms of doping abruptness and interface quality.