Effect of carbon on the valence band offset of Si/sub 1-x-y/Ge/sub x/C/sub y//Si heterojunctions

We have grown pseudomorphic single crystal Si/sub 1-x-y/Ge/sub x/C/sub y/ layers on Si (100) substrates by Rapid Thermal Chemical Vapor Deposition with up to 2.5% substitutional carbon. Capacitance-voltage as well as admittance spectroscopy measurements have been used to study the effect of carbon on the valence band offset of compressively strained Si/sub 1-x-y/Ge/sub x/C/sub y//(100) Si heterojunctions. The valence band offset of Si/sub 1-x-y/Ge/sub x/C/sub y//Si decreased by 25-30 meV as 1% carbon was added. Previous studies showed that 1% carbon increased the bandgap of strained Si/sub 1-x/Ge/sub x/ alloys by 21-26 meV, indicating that all the change in bandgap of Si/sub 1-x/Ge/sub x/ as carbon was added is accommodated in the valence band.