Electron paramagnetic resonance measurements on porous silicon

Electron paramagnetic resonance spectroscopy has been applied to investigate the properties of porous silicon formed on a (100)-oriented p-type silicon wafer prepared by anodisation. When anodisation was carried out in an electrolyte solution of HF(·H2O), H2O and C2H5OH with a volume ratio of 1 : 0 : 1, two different types of resonance were observed: one of which was of angular dependence which was coincident with the Pbl centre formed on the Si(100) surface, and the other was independent of the angle between the 〈011〉 axis of the silicon wafer and the applied magnetic field. For the porous silicon prepared in an electrolyte solution of HF(·H2O), H2O and C2H5OH with a volume ratio of 1 : 1 : 2 an angular-independent anisotropic signal with g⊥ = 2.0014 and g⊥ = 2.0064 was observed. This seemingly looks a signal with g = 2.005, but the difference g⊥ − g⊥ is larger than that for the dangling bonds in amorphous Si. It is therefore presumed that the resonances observed in this study are assigned to Pbl at the surface of Si(100) and Pb-like centres in nano-size crystallites.