High-Pressure Photoluminescence Studies of Pseudomorphic Si1-yCy/Si MQW Structures

Abstract

We have performed photoluminescence (PL) investigations of pseudomorphic Si 1-y C y /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, consists of bound and free exciton no-phonon lines and related Si transverse-optic phonon replicas. All MQW-related PL peaks shift to lower energy with increasing pressure at a rate characteristic for Γ-X indirect transitions in tetrahedral semiconductors. The total band offset and the activation energies for decay of the free and bound exciton emission increase slightly with pressure as a result of the larger negative band gap pressure coefficient of the strained pseudomorphic Si 1 -yCy layers compared to pure silicon. A separation of biaxial strain effects on the conduction and valence band near-gap states in the pseudomorphic Si 1-y C y layers (y < 0.02) on Si indicates a decrease of the intrinsic Si 1-y C y band gap which corresponds 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 localized in the SiC layers is inferred. This assignment is consistent with the dependence of PL-peak intensities and energies on excitation power, temperature and pressure.