Growth and electrical performance of heterojunction p⁺Si_1-x-yGe_xC_y/p^-Si diodes

We have fabricated heterojunction p⁺Si_1-x-yGe_xC_y/ p^-Si diodes. The SiGeC layers were grown epitaxially on Si (100) substrates by the rapid thermal chemical vapor deposition (RTCVD) technique using methysilane gas as a carbon precursor. The germanium concentration is 20% in these SiGeC alloys and the carbon concentrations are in the range of 0% to 1%. By studying the current-voltage characteristics of these diodes as a function of temperature the valence band discontinuities between SiGeC and Si layers were obtained as a function of carbon concentrations. We have found that the valence band discontinuity of the SiGe/Si heterostructure decreases by 11 meV when 1% of carbon is incorporated. Photoluminescence (PL) results show that 1% carbon increases the bandgap of strained p⁺SiGe alloys by 25 meV. This would imply that the conduction band discontinuity of SiGe/Si will decrease by 14 meV when 1% carbon is incorporated.