Paramagnetic defects in amorphous and microcrystalline silicon (a-Si:H and mu c-Si:H) with various structure compositions and doping levels were investigated by electron spin resonance (ESR). Samples were prepared by PECVD. The defect density was varied with 2 MeV electron bombardment at 100 K and stepwise annealing in the range of 80 K-433 K. In intrinsic material the spin density of the dominant ESR signal, presumably originating from dangling bonds (db), increases by up to 3 orders of magnitude after irradiation. In doped mu c-Si:H material the pronounced conduction electron (CE) resonance disappears after irradiation and is replaced by the db resonance like in the irradiated intrinsic material. Generally the initial spin density and the line shape can be restored upon annealing at 433 K. Additional features at g-values of g;approximate to,, 2.010 and g approximate to 2.000 in the ESR spectra are observed after irradiation together with the strongly enhanced Si db line at about g=2.004-2.005. These features decrease rapidly on the first annealing steps and cannot be observed after the final annealing stage. (C) 2006 Elsevier B.V. All rights reserved.