Humidity-voltaic characteristics of Ag-PS-Si structures

Abstract

Electrical characteristics of Ag-porous silicon (PS)-Si and PS-Si structures at the different ambient humidity and room temperature were investigated. Ag-PSSi structures have been fabricated by evaporation of Ag film onto the PS surface of PS-Si structures using electron-beam evaporator technique. It is shown that current-voltage characteristics of Ag-PS-Si structures strongly depend on ambient relative humidity (RH), whereas humidity-sensitiveness of electrical characteristics of PS-Si structures is weakly expressed. The humidity-voltaic effect, i.e. the origin of open-circuit voltage in Ag-PS-Si structures in humid atmosphere is discovered. The humidity-stimulated voltage approximately linearly increases with rise of the relative humidity. For the best Ag-PS-Si structure value of open-circuit voltage reached up to 350 mV at 90% RH. The possible mechanism responsible for humidity-stimulated generation of voltage in Ag-PS-Si structures is considered. The efficient photoluminescence from porous silicon (PS) observed by Canham [1] has stimulated extensive researches on formation mechanism of PS and physical mechanisms responsible for such luminescence [2]. Crystalline structure of PS is network of silicon nanometer-sized regions surrounded by void space with very large surface to volume ratios. PS surfaces are covered by silicon hydrides and silicon oxides. Surface bonds, in particular Si-H bonds play an important role in regulating of luminescence and other properties due to the large internal surface area of PS [3]. It is worth noting that environment influences on photoluminescence characteristics of PS [4]. The presence of water-vapor environment causes Si-Si bond breaking with formation Si-H bonds [5]. Influence of water on intensity of photoluminescence spectrum of PS is displayed in [6]. The porosity of the crystalline PS structure allows the fabrication of various different kinds of sensor device. Taliercio et al. [7, 8] suggested to use PS films as efficient membranes of oxygen sensors. Hydrogen detection with palladium modified porous silicon studied by Polishchuk et al. [9]. In Au-PS surface type structure Yamana et al. [10] discovered the dependence of the current on the relative humidity (RH) under applied voltage. A dependence of the reverse current of metalPS structure on the relative humidity was investigated by Dimitrov [11]. In this work the effect of ambient humidity on the current-voltage characteristics of Ag-PS diode structure is investigated. A rise of open-circuit voltage up to