Abstract
Electron paramagnetic resonance measurements have been made on samples of float zone silicon, implanted with 10^15 Er/cm2. One sample was coimplanted with oxygen to give an impurity concentration of 10^20 O/cm3 and 10^19 Er/cm3. In this coimplanted sample, sharp lines are observed which are identified as arising from a single spin 1/2 Er3+ center having a g tensor exhibiting monoclinic C1h symmetry. The principal g values and tilt angle are g1=0.80, g2=5.45, g3=12.60, and τ=2.6°. In the absence of O, the sharp lines are not observed. No Er3+ cubic centers were detected in either sample. Possible structures for the center are discussed