High-pressure photoluminescence studies of pseudomorphic Si1-yCy/Si MQW structures

We have performed photoluminescence (PL) investigations of pseudomorphic Si 1-yCy/Si (y = 0.45, 1.05, and 1.62%) multiple quantum well (MQW) structures under hydrostatic pressure (0 to 8 GPa) and at low temperatures (10 to 70 K). The main MQW-related emission, at energies below the Si band gap, consi sts of bound and free exciton no-phonon lines and related Si transverse-opt ic phonon replicas. All MQW-related PL peaks shift to lower energy with inc reasing pressure at a rate characteristic for Gamma-X indirect transitions in tetrahedral semiconductors. The total band offset and the activation ene rgies for decay of the free and bound exciton emission increase slightly wi th pressure as a result of the larger negative band gap pressure coefficien t of the strained pseudomorphic Si1-yCy layers compared to pure silicon. A separation of biaxial strain effects on the conduction and valence band nea r-gap states in the pseudomorphic Si1-yCy layers (y less than or equal to 0 .02) on Si indicates a decrease of the intrinsic Si1-yCy band gap which cor responds to that of pure silicon compressed to the lattice constant of the alloy. From this a type-I band alignment with electrons and light holes loc alized in the SiC layers is inferred. This assignment is consistent with th e dependence of PL-peak intensities and energies on excitation power, tempe rature :Ind pressure.