DIFFUSION OF HYDROGEN IN POROUS SILICON-BASED SENSORS

Abstract

Porous silicon (PS) layers of 65% porosity on n-type (111) Si substrates were prepared by anodic etching. Au/PS/Si structures have been fabricated by evaporation of thin Au film onto the PS surface. Current-voltage characteristics and the open-circuit voltage (Voc) generation in Au/PS/Si structures were examined at different ambient humidities (water vapor) in the temperature range 295-365 K. Generation of a voltage from 10 to 400 mV with the increase of the relative humidity from 50% relative humidity (RH) to 95% RH was observed in Au/PS/Si sensors. The response and recovery time of open-circuit voltage generated in Au/PS/Si Schottky-type sensors under humid atmosphere depends on ambient temperature. The effective diffusion coefficient of hydrogen estimated from response (or recovery) Voc − t curves on placing (or removal) of Au/PS/Si sensors in (or out) of humid ambient (90% RH) in the temperature range 313−363 K increases from 3.1 × 10−8 to 1.7 × 10−7 cm2/s and is described as D = 9.2 × 10−3 exp(−0.34 eV/kT). The possible mechanism of the hydrogen diffusion in porous silicon layers of Au/PS/Si sensors was considered.