Silicon clustering in Si-GaAs delta-doped layers and superlattices

To probe the development of Si-GaAs superlattices, we performed Si K-edge x-ray absorption measurements on periodic Si delta-doped structures in GaAs, for equivalent Si thicknesses of 0.02, 0.2, 0.5, 1, 2, and 4 monolayers (ML). We detected the presence of both Si-Si and Si-As (or Si-Ga) bonds and followed the variation of the coordination numbers as a function of the equivalent thickness of the Si layers. The Si-Si coordination number was found to gradually increase with increasing thickness, but Si-Si bonds were always detected, even at equivalent Si coverages of 0.02 ML. This indicates that the preferred growth conditions for Si-GaAs superlattices lead to widespread Si clustering and self-compensation, and suggests that lateral growth of such clusters to achieve coalescence may be the main mechanism for Si quantum well development.