Secondary ion mass spectrometry study of space-charge formation in thermally poled fused silica

Applying a dc electric field across a fused silica sample at elevated tempe ratures followed by cooling the sample with the field applied (thermal poli ng) leads to a second-order nonlinearity that has been linked to the format ion of a space-charge region in bulk glass. The first microscopic informati on on the extent of the space-charge region and its behavior with poling ti me is reported using secondary ion mass spectrometry to monitor the distrib ution of charged impurities. Lithium and sodium ions are observed to form d epletion regions. Potassium and sodium ions as well as a hydrogenated speci es appear to be injected from the surface. The extent of the space-charge r egion evolves approximately logarithmically with poling time well after the nonlinearity as measured by second-harmonic generation has been establishe d. The evolution of the space charge region can be qualitatively understood by an ion-exchange model that allows interaction of two ionic carriers wit h vastly different mobilities. (C) 1999 American Institute of Physics. [S00 21-8979(99)02524-4].