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

Abstract
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 bulk 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.