Characterization of high quality RTCVD relaxed Si1?xGex grown on ge graded buffer layers on Si by photoluminescence spectroscopy

Relaxed Si_1−xGe_x layers grown by rapid thermal chemical vapor deposition (RTCVD) have been characterized by photoluminescence (PL) spectroscopy. The structures consist of a Si_1−xGe_x capping layer with a 0.32 and 0.52 Ge concentration, grown on a compositionally graded Si_1−xGe_x buffer layer. The effect of the composition grading rate on the layer quality has been intensively studied. Well-resolved near band edge luminescence (excitonic lines with no-phonon and phonon replica similar as in bulk SiGe alloys) coming from the relaxed alloy capping layer and dislocation-related bands (Dl, D2, D3, D4 lines) in the graded buffer layer have been measured. The electronic quality of this relaxed capping layer, controlled by the design of the compositionally graded buffer layer, has been determined by the excitonic photoluminescence. A detailed analysis of the energy of the D4 dislocation band demonstrates that the main misfit dislocations remain confined in the first steps of the graded buffer layer. Si_1−xGe_x layers grown on these pseudo-substrates either under compressive or tensile strain and the well-defined PL results obtained are discussed on the bases of strain symmetrization and of high quality of the layers. This points out the possibility of using such high quality relaxed Si_1−xGe_x layers as substrates for the integration of new devices associated with Si technology.