Hydrogen detection on bare SiO2 between metal gates

Abstract

Metal–oxide–semiconductor capacitors with gates of Pd and Au forming a wedge of bare SiO2 between them are described. It is observed that the sensitivity to H2 in the wedge is larger than on the outside of the metal gates due to the different distribution of potential determined by the geometrical constraints. The local response of the surface is obtained through the use of a scanning light pulse technique (SLPT), showing photocurrent versus voltage curves shifted to more negative voltages upon exposure to hydrogen. Within the wedge there is a two-dimensional photocurrent pattern composed of two splitting photocurrent peaks, whose separation depends on the distance between Au and Pd contacts, and on the composition of the ambient. The transient response in the wedge is comparable to that of Pd gates and the possibility of detecting hydrogen (or other molecules) by measuring on the bare insulator surface provides new possibilities for the use of field-effect structures for gas sensing. A semiempirical model describing the SLPT response for this particular geometry, conforms to experimental features, and highlights the sensitivity of the distribution of potential in the wedge to the density of charges induced on the semiconductor surface.