By preparing a junction between Al and porous p-type Si, a sensor was obtained in which the current was increased by up to 2 orders of magnitude in the presence of various gases. In order to interpret this phenomenon, it was assumed that the conductivity was governed by the width of a channel that resulted from the partial depletion of Si between 2 pores. This depleted region was attributed to charges that were trapped on surface states which were associated with the Si/SiO2 interface; where SiO2 was the native oxide. It was concluded that when some gas was adsorbed, mainly on Si-H bonds, electrical screening of the interface states occurred. These states were mainly dangling bonds that existed in the neighborhood of the Si-H bonds.

D.Stievenard, D.Deresmes: Applied Physics Letters, 1995, 67[11], 1570-2