PHONON-RESOLVED PHOTOLUMINESCENCE AT LAMBDA=1.55 MU-M FROM UNDULATINGSI0.5GE0.5 EPITAXIAL LAYERS

Si0.5Ge0.5/Si multiquantum well structures are grown using a productio n-compatible ultrahigh vacuum chemical vapor deposition system. The st ructures are designed in order to obtain dislocation-free undulating s trained layers. A photoluminescence emission corresponding to the dire ct ''no phonon'' transition is measured at energies systematically sma ller than calculated far planar layers, implying that any increase in band gap due to elastic relaxation of the lattice strain at the undula tion crests is compensated for by a confinement energy decrease togeth er with a Ge accumulation at the undulation crests. The photoluminesce nce ''no phonon'' emission peaks at a wavelength that increases with n ominal well thickness up to 1.55 mu m. This opens the possibility of u sing dislocation-free silicon-germanium undulating layers as an absorb er for photodetector applications at the telecommunication wavelengths of lambda = 1.3-1.55 mu m. (C) 1998 American Institute of Physics [S0 003-6951(98)01219-4].