Measurement of the conduction band offsets in Si/Si1-x-yGexCy and Si/Si1-yCy heterostructures using metal-oxide-semiconductor capacitors

Metal-oxide-semiconductor (MOS) capacitors fabricated on in situ doped n-ty pe Si/Si1-x-yGexCy and Si/Si1-yCy epitaxial layers were used to study the c onduction band offsets in these heterojunctions. The heterostructures were grown epitaxially in a rapid thermal chemical vapor deposition reactor. Si/ Si1-x-yGexCy samples with a nominal Ge concentration of 20 at. % and carbon fractions up to 1.3 at. % were studied. Carbon fractions up to 1.6 at. % w ere studied for the Si/Si1-yCy samples. Gate oxides were formed by thermal oxidation of the Si cap at 750 degrees C. X-ray diffraction measurements co nfirm that the processing did not affect the strain in the layers. Devices exhibit well-behaved high frequency and quasistatic capacitance-voltage (C- V) characteristics indicating the high electronic quality of the material. Capacitance-voltage measurements performed over a range of temperatures wer e used to extract the band offsets. Confinement of electrons at the heteroi nterface is apparent in the C-V curves of the Si/Si1-yCy MOS capacitors. Co mparison of the measured C-V data to one-dimensional device simulations yie lds a conduction band edge lowering of similar to 65 meV per at. % C in the Si1-yCy samples. The Si1-x-yGexCy samples, on the other hand show no evide nce of electron confinement. Based on a sensitivity analysis of this techni que, it is estimated that the conduction band offset in these samples is le ss than 30 meV. The smaller offsets in Si/Si1-x-yGexCy compared to Si/Si1-y Cy can be explained by the competition between strain compensation and the intrinsic chemical effect of carbon in Si1-x-yGexCy. (C) 1999 American Inst itute of Physics. [S0021-8979(99)07702-6].