Modulation-doped n-type Si/SiGe with inverted interface

We report the growth of n-type modulation-doped Si/SiGe with the doped SiGe supply layer underneath the strained Si channel. The mobility and charge density are measured in samples with 2- and 3-nm-thick spacers using gated Hall measurements. A peak room temperature mobility of 2200 cm2/V s is measured at a sheet density of 2.5×1012 cm-2. The measurements indicate a clear mobility modulation especially near threshold. Our layer design allows the gate to induce a sheet charge density of up to 3.2×1012 cm-2, before any significant reduction in the mobility is observed.