Systematics of electron mobility in Si/SiGe heterostructures

Abstract

We have investigated limits to the low temperature electron mobility in modulation-doped Si/SiGe heterostructures grown by ultrahigh vacuum chemical vapor deposition. The temperature dependence and peak value of the mobility suggest that interface roughness is the chief scattering mechanism in samples with a thin buffer layer below the channel. Up to about 2 μm, increasing the thickness of the buffer layer raises the mobility. We have also observed a systematic increase of electron mobility with spacer (or setback) thickness, which is characteristic of remote ion scattering. The influence of background impurities is seen in the decrease of mobility with decreasing two-dimensional gas density.