A study of defects in amorphous silicon films

Positron lifetime measurements have been performed in an investigation of amorphous silicon films deposited on single-crystal silicon wafers. The amorphous films were produced by evaporation in vacuum or by sputtering in an atmosphere of either pure argon or a mixture of argon and fluorine. All films gave rise to a new lifetime component τ2 having values in the range of 400 to 500 ps. As many as 70% of the positrons annihilating in the film were calculated to be trapped by defects in the film. During isochronal annealing, the τ2 component disappeared around 700 °C for the evaporated films, while it persisted at least up to 1300 °C for the sputtered films. Another lifetime with a value of 2 ns was also observed. This lifetime had a constant intensity of 0.2 to 0.3% for both evaporated silicon and sputtered silicon using argon gas. For the sputtered film using both argon and fluorine, the intensity of this component was increased by a factor of 10 after annealing at 1100–1300 °C.