Modeling Si nanoprecipitate formation in SiO2 layers with excess Si atoms

Computer simulations based on the Monte Carlo method are used to analyze pr ocesses leading to the formation of luminescence centers in SiO2 implanted with Si ions. The simulations, which take place in a two-dimensional space, mimic the growth of silicon nanoprecipitates in layers containing several at. % of excess silicon. It is assumed that percolation clusters made up of neighboring Si atoms form first. As the annealing temperature increases, t hese clusters grow and compactify into nano-sized inclusions of a well-defi ned phase. It is shown that a dose dependence arises from an abrupt enhance ment of the probability of forming direct Si-Si bonds when the concentratio n of silicon exceeds similar to 1 at. %. Under these conditions, percolatio n chains and clusters form even before annealing begins. The effect of the temperature of subsequent anneals up to 900 degrees C is modeled via the we ll-known temperature dependence of Si diffusion in SiO2. It is assumed that annealing at moderate temperatures increases the mobility of Si atoms, the reby facilitating percolation and development of clusters due to an increas e in the interaction radius. Intrinsic diffusion processes that occur at hi gh temperatures transform branching clusters into nanoprecipitates with wel l-defined phase boundaries. The dose and temperature intervals for the form ation of precipitates obtained from these simulations are in agreement with the experimental intervals of dose and temperatures corresponding to the a ppearance of and changes in luminescence. (C) 1999 American Institute of Ph ysics. [S1063-7826(99)00204-5].