The optically active center and its activation process in Er-doped Si thin film produced by laser ablation

The local structure of erbium-doped silicon produced by the laser ablation technique is investigated by Er L-III-edge x-ray absorption fine structure analysis. The combined analysis of extended x-ray absorption fine structure analysis and an x-ray absorption near-edge structure simulation based on multiple-scattering theory reveals the most probable atomic coordination of the optically active center; Er bonded with six oxygen atoms has a C-4 upsilon symmetry. The optical activation process of this system is also discussed. The Si target with 10 wt% Er2O3 has two kinds of local structures, C-rare-earth Er2O3 grain and another Er phase incorporated in Si. The laser ablation homogenizes these phases, and deposits a new single-phase structure of the octahedron (O-h point group) on the substrates. In this phase, the optical transition probability is low due to the forbidden 4f transition of Er in the crystal field originating from the higher-order symmetry of O. After annealing, degradation of the symmetry from O-h to C-4 upsilon results in a crystal field suitable for inducing sufficient radiation transition. (C) 1999 American Institute of Physics. [S0021-8979(99)04508-9].