Overcharging of porous silicon localized states at gas adsorption
The behaviour of localized states in Pd/nano- or mesoporous Si/p-Si heterojunctions is studied by the DLTS technique in a vacuum and different atmospheres: ambient air, Ar, N2, CO2, O2. The complex DLTS spectra of both signs related to electron and hole traps in porous Si are detected. The intensity of DLTS peaks and activation energy is shown to be dependent on the morphology of the porous layers and ambient atmosphere in which DLTS measurements were carried out. The shift of activation energy with increase of the applied reverse voltage is interpreted from the point of view of a spatially inhomogeneous distribution of localized states in a porous layer. The cyclic transformation of DLTS spectra is observed for consecutive measurements in a vacuum and ambient atmosphere. Oxygen adsorption (at partial pressure of a few mbar) results in strong passivation of deep traps in mesoporous Si.