Characterization of a new sensing device based on hydrocarbon groups (CH x ) coated porous silicon H. Cheraga, S. Belhousse, N. Gabouze * UDTS, 2 bd. Frantz Fanon, B.P. 399 Alger-Gare, Algiers, Algeria Available online 19 July 2004 Abstract A gas sensing device based on hydrocarbons (CH x )/porous silicon structure was fabricated. Porous silicon was prepared by electrochemical etching of p-type silicon in HF/ethanol (50/50) by volume. The porous samples were coated with hydrocarbons groups deposited by plasma of methane. Sensitivity of these devices, response time and capacitance response to different gas exposure (ethane, ethylene and propane) have been investigated. Current–voltage and capacitance–voltage characterizations show that heterojunction are modified by the gas reactivity on the PS/CH x surface. Based on these results and IR spectroscopy measurements, mechanism of electrical conduction was interpreted in term of charge carrier transport through shallow traps associated with the surface. Finally, it was noted that, after 6 months, our sensor preserves its features such as, short response time, stability and reproducibility. # 2004 Elsevier B.V. All rights reserved. Keywords: Porous silicon; Gas sensor; Thin films 1. Introduction There has been considerable interest in the last years in gas sensors based on porous silicon. Gen- erally, porous silicon sensing properties observed are changes of electrical capacitance in presence of gases and the quenching of photoluminescence [1,2].A high sensitivity of the PS layer was observed for organic vapors with high dipole moments [3,4]. How- ever, the electrical response of the PS layer for the organic vapors can lead to remarkable differences depending on the PS layer for the oxidation of the PS surface. Recently, we have fabricated a gas sensing device based on hydrocarbons (CH x )/porous silicon structure. We found that heterojunction fabricated from thin CH x layer shows a good rectifying behavior. With the porous silicon sensitivity to the gas environments, the last property has been used to gas sensor devices whose electrical characteristics were modified by the gas reactivity on the PS surface. In addition FT-IR measurements in ethylene, ethane or propane environment [5] show a reversible free- carrier detraping in the IR region of the spectra. In this work, we performed current–voltage (I–V), capaci- tance–voltage (C–V) and conductance–voltage (G–V) measurements (at different frequencies) on CH x /PS/p- Si diodes. Generally, chemical sensors based on PS layers are used to examine chemical concentrations in the liquid or gas phase by observing a variation of conductance of capacitance of these devices. Applied Surface Science 238 (2004) 495–500 * Corresponding author. Tel.: þ213 21 43 35 11; fax: þ213 21 43 35 11. E-mail address: ngabouze@caramail.com (N. Gabouze). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.05.249