Photoluminescence decay of direct and indirect transitions in Ge/SiGe multiple quantum wells

Abstract

We present a detailed experimental study of the photoluminescence decay of direct Γ-Γ and indirect L-Γ transitions in compressively strained Ge/Si0.15Ge0.85 type I multiple quantum wells. The lifetime of the fundamental L-Γ indirect-gap related transition is in the 6 to 13 ns range at the lattice temperature of 14 K. These values are just one order of magnitude higher than those typical of type-I direct gap III-V quantum wells and are significantly shorter than those characteristic of type-II indirect gap SiGe/Si quantum wells. The measured decay times show a clear dependence on the quantum well width and lattice temperature. The decay of the Γ-Γ direct-gap related transition is dominated by the ultrafast electron scattering from Γ-type to L-type states of the conduction band.