Electrically active point defects in amorphous silicon nitride: An illumination and charge injection study

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Abstract
We observe a strong correlation between changes in the density of paramagnetic silicon ‘‘dangling-bond’’ centers and changes in the space-charge density in amorphous silicon nitride films subjected alternately to illumination and both positive- and negative-charge injection. We demonstrate that ultraviolet illumination annihilates space charge and creates stable paramagnetic centers in silicon nitride. These centers can be passivated with a 1-h anneal at 250 °C. Our results provide the first direct experimental evidence associating a specific point defect with the trapping phenomena in amorphous silicon nitride. We also demonstrate both directly and for the first time the amphoteric nature of the silicon nitride dangling-bond center. Furthermore, our ability to cycle the defect between its paramagnetic neutral state and both its charged diamagnetic states suggests that the optical generation of dangling bonds in amorphous silicon nitride involves no complex structural rearrangement, but simply changes in the charge and spin states of the defect.