Electrical properties of Si1-xCx alloys and modulation doped Si/Si1-xCx/Si structures

We report electrical properties of undoped and Sb-doped Si1-xCx alloys grown by molecular beam epitaxy. Nominally undoped alloy layers exhibit electron background levels of 4 x 10(16) cm(-3) with a mobility above 30 000 cm(2)/V s at low temperatures. The layers can be doped with Sb at low growth temperatures, and the carrier concentrations and mobilities obtained are comparable to similarly doped Si layers. Modulation-doped Si/Si1-xCx/Si structures with the modulation doping in the Si layer close to the surface exhibit enhanced electron mobilities with peak values of about 10 000 cm(2)/V s, indicating that Si1-xCx strained on a silicon substrate forms an electron channel. From the saturation carrier concentration at low temperatures, the electron barrier between Si and Si0.98C0.02 is estimated to be about 150 meV. In lightly doped channel structures carrier freeze-out at low temperatures is observed, indicating a relatively high defect density in the channel. (C) 1995 American Institute of Physics.