NATURE OF ELECTRON-SPIN-RESONANCE CENTERS IN POROUS SILICON

The nature of the defects in porous silicon has been studied by electr on spin resonance (ESR) measurements. From an analysis of the ESR spec tra which have an angular dependence, we show that the main defect has trigonal symmetry with a principal axis along the < 111 >> axis and t hat the principal values of the g-tensor, g(parallel to) and g perpend icular to, are 2.0022 and 2.0078, respectively. This defect is identif ied as a silicon dangling bond in the region which retains the crystal linity of the substrate. We have also observed light-induced defect cr eation and photoluminescence (PL) fatigue associated with it. These ch anges are partly, but not completely, recovered by thermal annealing, unlike hydrogenated amorphous silicon. Since an increase of the ESR sp in density due to the illumination results in a decrease of PL intensi ty, it is concluded that the Si dangling bond acts as a nonradiative c enter. Furthermore, we have observed a change of the ESR line shape in the case of prolonged illumination. We also discuss the origin of thi s change.