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Published online by Cambridge University Press: 28 February 2011
The absorption of CO2 laser radiation in doped silicon is dominated by free-carrier transitions, which is an extrinsic absorption property. For applications where one would like to preferentially deposit the pulse energy in heavilydoped layers, the CO2 laser is found to be preferable to other laser systems that oscillate at a photon energyexceeding the bandgap.The advantages of laser processing with below-bandgap radiation are illustrated by three different applications that areeither impossible or much more difficult to achieve with a visible or ultraviolet laser: (1) the melting of buried layerswithout melting the material that encapsulates the molten layer, (2) the melting of shallow layers at the surface, and(3)the annealing of lattice imperfections caused by high-temperature diffusion of phosphorus dopants into small diffusion wells.