Dopant site analysis of heavily Si-doped GaAs using a combination of electron microscopy and synchrotron radiation

Silicon (Si) acts as an amphoteric impurity in gallium arsenide (GaAs), occupying various sites and exhibiting different coordination structures within the material. In this study, we employed electron microscopy, x-ray absorption spectroscopy, and theoretical simulations to analyze the Si-occupied sites and local coordination structures at concentrations ranging from 2 to 4 × 1019 atoms/cm3 in heavily doped GaAs. High angular resolution electron channeling x-ray spectroscopy was employed to analyze the Si-occupied sites. This method quantitatively estimates site occupancies through statistical analysis of atom site-dependent spectra. It was observed that Si substitutes for both Ga and As sites with nearly equal occupancies. Si K-edge x-ray absorption fine structure (XAFS) measurements and density functional theory calculations were used to explore the local coordination structures of Si. The peak positions of experimental XAFS spectra aligned closely with those of the calculated XAFS spectra for neutral SiGa–SiAs dumbbells, particularly when Si atoms were in close proximity. Considering the effect of vacancies, the experimental XAFS peak position corresponded well with that of the calculated Si dumbbell–VAs pair. In addition, the observed pre-peak was attributed to neutral Si, likely originating from Si clusters. These findings enhance our understanding of Si-related defect structures and their influence on the properties of heavily Si-doped GaAs.