Local microstructures of Si in GaN studied by x-ray absorption spectroscopy

Si K-edge x-ray absorption spectroscopy (XAFS) has been used to study the local structure of Si dopant in GaN crystalline material. Doping concentrations NSi from 8.0×1016 to 4.4×1019 cm−3 were investigated. It is observed that the near-edge spectra vary significantly as a function of NSi. At low concentrations the Si K-edge spectra exhibit features similar to that obtained from N K-edge measurement, while at high concentrations the near-edge spectra shape is similar to that recorded from Si3N4. We interpret the results as an indication that Si is not randomly distributed. The changes of the near-edge spectra as a function of doping level is explained as due to changes in the magnitude of Si local lattice contraction caused by the formation of various types of Si clusters. The interpretation is further supported by extended XAFS spectra analysis. A Si-induced strain-field near the surface is proposed as the main force for the cluster formation during epitaxial growth.