ELECTRICAL-PROPERTIES OF THERMALLY OXIDIZED POROUS SILICON

A detailed electrical investigation of oxidized porous silicon (OPS) h as been undertaken, using metal oxide semiconductor capacitors. We dem onstrate that the dielectric can provide good electrical isolation und er moderate electric fields, exhibiting low leakage current, high resi stivity reasonably low interface state density, and fixed charge level . The total density of electron traps in the OPS was found to be of th e order 10(12) cm(-2) with the charge centroid lying within the oxidiz ed porous silicon layer, rather than in the underlying bulk thermal ox ide or OPS/Si interfaces. The conduction mechanism at higher fields ni as found to be rather sensitive to the substrate type and hence the mi crostructure of the OPS and possible metallic contamination. Conductio n limiting mechanisms of the tunneling type (temperature insensitive), Poole-Frenkel thermally activated type, and an anomalous conduction ( negative temperature dependence) were observed on several typical wafe rs. We attribute the low barrier height of 0.9 eV, extracted from the samples exhibiting tunneling conduction, to localized injection arisin g from interfacial asperities. A dominant donor-like trap with depth o f 0.9 eV from the conduction bandedge was found in p-type samples show ing Poole-Frenkel conduction. Evidence is presented that stress/strain may play a role in the anomalous conduction seen in n-type samples.