The origin of photoluminescence in Ge-implanted SiO2 layers

Ge ions were implanted at 100 keV with 3 x 10(16) cm(-2) into a 300 nm thick SiO2 layer on Si. Visible photoluminescence (PL) around 2.1 eV from an as-implanted sample is observed, and faded out by subsequent annealing at 900 degrees C for 2 h. However, PL shows up again after annealing above 900 degrees C at the same peak position. Compared with the as-implanted sample, significant increase of Ge-Ge bonds is measured in X-ray photoelectron spectroscopy, and the formation of Ge nanocrystals with a diameter of 5 nm are observed in transmission electron microscopy from the sample annealed at 1100 degrees C. We conclude that the PL peak from the sample annealed above 900 degrees C is caused by the quantum confinement effects from Ge nanocrystals, while the luminescence from the as-implanted sample is due to some radiative defects formed by Ge implantation. (C) 1999 Elsevier Science B.V. All rights reserved.