Influence of interdiffusion and surfactants on Si/SiGe heterointerfaces

Molecular beam epixaxially grown SiGe single quantum wells were investigated by photoluminescence techniques and secondary ion mass spectrometry. For all experiments nominally identical SiGe quantum wells with a width of 4 nm and a Ge concentration of 20% were used. A shift to higher energies of the near-band-edge emission for single quantum wells grown at temperatures above 850°C is attributed to interdiffusion and segregation of Si and/or Ge at the heterointerface. The diffusion process was simulated by a model and it is shown that the observed behaviour can be explained in terms of two different diffusion mechanisms: diffusion via lattice site exchanges and point defect-induced diffusion. In another set of experiments, segregation effects which can additionally deform the shape of the Ge concentration profile and therefore the potential profile, have been investigated separately. All our results were established by secondary ion mass spectrometry.