Investigation of humidity adsorption in porous silicon layers



The dependence of humidity adsorption in porous silicon (PS) layers on the fabrication conditions (current density and oxidation) has been investigated. As-prepared and additionally oxidized PS layers have been investigated using physical gas (N2) adsorption measurement at 77 K, water vapor adsorption measurements at room temperature, impedance spectroscopy and contact angle measurement. Pore size distributions and specific surface areas have been calculated using the BJH and BET model. Additional oxidation of porous layer promotes the humidity adsorption and improves the wetting compared to as-fabricated porous Si layers. The correlation between adsorption isotherms, electrical parameters and surface effects are presented and discussed in respect to the use of PS for humidity sensing. Oxidation of PS layers improves the sensitivity of PS based humidity sensors considerably. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)