Papers by Author: D. Oren

Abstract: Current-voltage characteristics of Schottky-type Ag/Porous Silicon (Ag/PS) structures in normal air, humid ambient and in different hydrogen-containing solutions (distilled water, freshwater, Black sea-water, ethanol ad methanol) have been investigated. Generation of the opencircuit voltage (Voc), short-circuit current (Jsc) up to 560 mV and 0.5mA/cm2, respectively, on placing Ag/PS structures in hydrogen-containing solutions was discovered. This phenomenon is reversible, i.e. placing and removal of Ag/PS structures cell from hydrogen-containing solutions is accompanied by response and recovery of the Voc and Jsc parameters. It is shown that the thermal annealing of the Ag/PS structure at 200oC for 10 min is accompanied by somewhat changes and stabilization of Voc and Jsc parameters of Ag/PS sensors. The possible mechanisms related with hydrogen-stimulated generation of voltage and diffusion-stimulated stabilization of the sensing parameters of Ag/PS Schottky-type structures is suggested. Data received in this work indicate on perspectivity of using Ag/PS structures as both the gas sensors and hydrogen cells.

Abstract: Porous silicon (PS) layers with porosity of 60% on n-type (111) Si substrates were prepared by anodic etching under the white illumination. Metal (Cu, Ag or Au)/PS/Si and metal (Cu, Ag or Au)/Si structures have been fabricated by evaporation of thin metal film onto the PS or Si surface, respectively. The diffusion annealing of structures was carried out in air at 100-250oC. Examination of Cu, Ag and Au concentration distribution in PS layer and monocrystalline Si substrate was performed by successive removal of thin layers from sample and measuring the energy dispersive X-ray fluorescence (EDXRF) intensity of CuKα1, AgKα1 and AuLβ1 peak. The effective diffusion coefficients for investigated metals along PS surfaces decrease in series Cu, Ag and Au and temperature dependences are described as D(Cu)=7.8 exp(-0.62eV/kT), D(Ag)=4.2x10 exp(-0.72eV/kT) and D(Au)=1.2x102 exp(-0.81eV/kT). Diffusion coefficients of Cu, Ag and Au along PS surfaces are larger (by a factor of 104-105) than those into monocrystalline Si. The diffusion mechanism of Cu, Ag and Au along PS surfaces is discussed and data on influence of diffusion of these metals on humidity-sensitive characteristics of metal(Cu, Ag or Au)/PS Schottky type gas sensors is also presented. Diffusion of metals of I group in PS is accompanied by increase of humidity-sensitivity of metal/PS structures by a factor of 1.2-1.4.