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 l ocal structure of Si dopant in GaN crystalline material. Doping concentrati ons N-Si from 8.0x10(16) to 4.4x10(19) cm(-3) were investigated. It is obse rved that the near-edge spectra vary significantly as a function of N-Si. A t 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 f ormation of various types of Si clusters. The interpretation is further sup ported by extended XAFS spectra analysis. A Si-induced strain-field near th e surface is proposed as the main force for the cluster formation during ep itaxial growth. (C) 1999 American Institute of Physics. [S0003-6951(99)0112 7-4].