Fundamental properties of silicon films crystallized by a 30-ns-pulsed XeCl excimer laser were discussed. Although crystallization of 50-nm thick silicon films formed on quartz substrates occurred through laser heating at the crystalline threshold energy density of 160 mJ/cm~2, a higher laser energy density at 360 mJ/cm~2 was necessary to crystallize silicon films completely. Analyses of free carrier optical absorption revealed that phosphorus-doped silicon films with a carrier density about 2x10~(20) cm~(-3) had a high carrier mobility of 20 cm~2/Vs for irradiation at the crystallization threshold energy density, while Hall effect measurements gave a carrier mobility of electrical current traversing grain boundaries of 3 cm~2/Vs. This suggested that the crystalline grains had good electrical properties. As the laser energy density increased to 360 mJ/cm~2 and laser pulse number increased to 5, the carrier mobility obtained by the Hall effect measurements markedly increased to 28 cm~2/Vs because of improvement of grain boundary properties, while the carrier mobility obtained by analysis of free carrier absorption increased to 40 cm~2/Vs. A post annealing method at 190 deg C with high-pressure H_2O vapor was developed to reduce the density of defect states. Increase of carrier mobility to 500 cm~2/Vs was demonstrated in the polycrystalline silicon thin film transistors fabricated in laser crystallized silicon films.
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