Comparison of Si/Si1-x-yGexCy and Si/Si1-yCy heterojunctions grown by rapid thermal chemical vapor deposition

The materials and electronic properties of Si/Si1-x-yGexCy and Si/Si1-yCy heterojunctions grown by rapid thermal chemical vapor deposition are compared. Substitutional carbon incorporation is readily achieved in Si1-x-yGexCy alloys by the addition of a carbon precursor such as ethylene or methylsilane during growth, using germane and dichlorosilane as the germanium and silicon sources respectively. In contrast, a significant fraction of the carbon is not substitutional in Si1-yCy films grown using dichlorosilane in combination with either carbon source. A highly reactive silicon source, such as silane, enables the growth of high quality Si1-yCy. Good agreement between the substitutional carbon concentration extracted from X-ray diffraction and the total carbon concentration measured by secondary ion mass spectrometry is observed in Si1-yCy alloys grown at 550 degrees C with silane, for carbon contents up to about 1.8 at.%. Si/Si1-x-yGexCy and Si/Si1-yCy metal-oxide-semiconductor capacitors show well-behaved electrical characteristics. Analysis of the capacitance-voltage data indicates that the band offsets are primarily in the valence band for Si/Si1-yGexCy and the conduction band for Si/Si1-yCy heterojunctions. The conduction band is lowered as carbon is added to Si and the effect is larger than expected from strain alone. (C) 1998 Elsevier Science S,A. All rights reserved.