Interface-related defects in a Ge0.4Si0.6/Si single well

Abstract

Deep-level transient spectroscopy measurements were performed on a Ge0.4Si0.6/Si single quantum well grown by molecular beam epitaxy. The results show hole traps labelled H1 and H2. H1 is a deep level in Si whose activation energy measured from the valence band and capture cross section are 0.3 eV and 3*10-22 cm2 respectively. When an electric field was applied to the quantum well, an anomalous behaviour was observed for H2 only. The activation energy of H2 increased and then saturated as the applied electric field increased. Such behaviour can be explained by identifying H2 as an emission from interface states to a bound state in a quantum well. The depth profile of H2 also showed a spatially confined behaviour which strongly supports the idea that H2 is an interface state. Calculations using a variational method were performed to determine the bound state energy levels of the quantum well in a constant electric field. Comparing the results of experiments with those of the calculations, H2 corresponds to an interface state whose energy level lies at 0.45 eV above the valence band edge of the well; the capture cross section of H2 is 2.1*10-18 cm2.