Initial stages of porous silicon formation: An in‐situ investigation of the electronic properties and surface morphology

Abstract

In-situ photovoltage (PV) and photoluminescence (PL) are used to obtain information about the band bending of Si and the PL quenching by nonradiative (nr) surface recombination during the beginning of electrochemical etching of silicon in aqueous fluoride solutions. The onset of the porous silicon formation in diluted NH4F solution is accompanied by an increase of nr surface recombination, by a development of positive charged surface states and by a strong increase of the current density. The evolution of hydrogen and its penetration into near surface regions lead at first to the passivation and with ongoing time to the formation of nr surface defects. The lowest rate of nr surface recombination has been observed in highly concentrated HF solution just in the beginning of the electrochemical etching process. Therefore, intermediates of these reactions are rather of ionic nature than like Si dangling bonds. Scanning electron microscopy reveal the slight roughening of the Si surface and infrared spectroscopy confirm that these surfaces are always hydrogenated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)