Electrical measurements on MBE grown Si/Si_1-xGe_x heterojunctions

Electrical measurements were made on Si/Si_1-lxGe_x, n-n heterojunctions grown by MBE on Si 〈100〉 substrates. The carrier concentration profile derived from capacitance-voltage measurements gives a determination of the conduction band discontinuity. We found for a strained Si layer on a relaxed Si_0.75Ge_0.25 layer that the Si conduction band is lower by 0.12 eV than the alloy band. In the case where the alloy layer is strained, the conduction band is still lower on the Si side but the magnitude of the discontinuity is small. C-V measurements on a partially relaxed layer show deep levels appearing at the interface. Cross-sectional TEM revealed defects at the interface which are correlated with the electrical states.