Deep-level transient spectroscopic measurements were performed on Si0.6Ge0.4/Si single quantum-wells which had been grown by molecular beam epitaxy. The results revealed hole traps which were labelled H1 and H2. The former was a deep level in Si whose activation energy (with respect to the valence band) and capture cross-section were 0.3eV and 3 x 10-22cm2. When an electric field was applied to the quantum well, an anomalous behavior was observed only in the case of H2. The activation energy of H2 increased, and then saturated, as the applied electric field was increased. This behavior could be explained by supposing that H2 was an emission from interface states to a bound state in a quantum well. The depth profile of H2 also exhibited a spatially confined behavior which strongly supported the idea that H2 was an interface state. Calculations which were based upon a variational method were used to determine the bound-state energy levels of the quantum well in a constant electric field. By comparing experimental data with the calculations, it was deduced that H2 corresponded to an interface state whose energy level lay 0.45eV above the valence band edge of the well. The capture cross-section of H2 was 2.1 x 10-18cm2.

T.W.Kang, W.J.Park, C.K.Chung, J.S.Park, K.L.Wang, T.W.Kim: Semiconductor Science and Technology, 1995, 10[2], 179-82