Phonon-resolved photoluminescence at λ=1.55 μm from undulating Si0.5Ge0.5 epitaxial layers

Abstract

Si 0.5 Ge 0.5 /Si multiquantum well structures are grown using a production-compatible ultrahigh vacuum chemical vapor deposition system. The structures are designed in order to obtain dislocation-free undulating strained layers. A photoluminescence emission corresponding to the direct “no phonon” transition is measured at energies systematically smaller than calculated for planar layers, implying that any increase in band gap due to elastic relaxation of the lattice strain at the undulation crests is compensated for by a confinement energy decrease together with a Ge accumulation at the undulation crests. The photoluminescence “no phonon” emission peaks at a wavelength that increases with nominal well thickness up to 1.55 μm. This opens the possibility of using dislocation-free silicon–germanium undulating layers as an absorber for photodetector applications at the telecommunication wavelengths of λ=1.3–1.55 μm.