Electron paramagnetic resonance of porous silicon: Observation and identification of conduction-band electrons

New features in electron paramagnetic resonance (EPR) of porous silicon have been examined here. A new isotropic EPR center was observed at g = 1.9995(1) at T = 4.2 K, in both p-type and n-type porous silicon. By comparing its g value with those of shallow donors in bull; silicon, the center was identified due to the conduction-band (CB) electrons in silicon microcrystals. The CB signal, present in freshly prepared p-type and n-type samples, can be dramatically and surprisingly enhanced by the presence of a polar solvent on the n-type porous silicon surface. Even though it was shown that most of the donor electrons in an n-type sample can be pulled into the porous layer from the substrate by solvent exposure of the porous layer, the possible electrochemical effects are not yet completely understood; to establish a reasonable model for them would require appropriately controlled experiments. (C) 1997 American Institute of Physics.