Near-band-gap photoluminescence from pseudomorphic Si1−xGex single layers on silicon

Abstract

The systematic study of band‐edge luminescence in pseudomorphic Si/Si_1−xGe_x/Si double‐heterostructure layers is reported for a wide composition range, 0.12<xxE^S_X(x) = 1.155−0.874x+0.376x² eV. Addition of an expression for the exciton binding energy provides an approximation for the energy difference between the alloy valence band and the lowest conduction‐band edge at low temperature. An exciton upshift of 16.9 meV due to quantum confinement is observed in a 6.3‐nm Si_0.83Ge_0.17 alloy well. This is consistent with either type‐I or type‐II band alignment for which the conduction‐band offset has a magnitude ‖ΔE_c‖ ≤ 10 meV. The excitonic hole is closely confined in the alloy but the spectra suggest that the electron density in the silicon barriers is increased for the thin layer.