| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Thursday Sessions |
| Session TF+EM+SS-ThA |
| Session: | Applications of Self Assembled Monolayers |
| Presenter: | Girjesh Dubey, NRC-SIMS, Canada |
| Authors: | G. Dubey, NRC-SIMS, Canada F. Rosei, INRS-EMT, Canada G.P. Lopinski, NRC-SIMS, Canada |
| Correspondent: | Click to Email |
Adsorption of charged or polar species on semiconductor surfaces can modulate the electrical properties through long-range field effects. Hydrogen-terminated silicon-on-insulator ( SOI-H) is an interesting model system for investigating this sensitivity to surface processes [1,2]. Accumulation mode SOI-H pseudo-MOSFETs [3] have been used to probe molecular adsorption and reaction events. Current-voltage characteristics of such n-channel devices are found to be sensitive to the environment, with the accumulation threshold voltage, or flat-band voltage (VFB), exhibiting large reversible changes upon cycling between ambient atmosphere, high vacuum (<10-5 Torr) and exposure to water and pyridine vapour at pressures in the torr range. Both these adsorbates act as effective electron donors, shifting the flat band potential to more negative values. The field-effect mobility is found to be comparatively less affected through these transitions. Adsorption of the well known electron acceptor tetracyanoethylene (TCNE), is shown to cause depletion, with ppm levels of TCNE vapour in ambient atmosphere found to rapidly decrease the saturation current by over two orders of magnitude. The effect is only partially reversible on the hydrogen terminated surface, due to the accumulation of strongly bound TCNE molecules on the surface. In addition, oxidation of the H-terminated surface is seen to result in irreversible shifts in both the flat-band voltage and field-effect mobility. In order to passivate the surface from these irreversible processes, a photochemical gas phase reaction [4] with decene was used to form a decyl monolayer on the SOI(100)-H surface. Formation of this monolayer is found to result in a relatively small shift of threshold voltage and only a slight degradation of the field effect mobility. Decyl passivation only slightly decreases the response of the FET to TCNE adsorption while significantly improving the reversibility of the response. These results suggest that alkyl monolayer dielectrics formed by the gas phase photochemical method can function as good passivating dielectrics in field effect sensing applications.
[1] G. Dubey, G.P. Lopinski, and F. Rosei, Appl. Phys. Lett. 91, 232111 (2007).
[2] G. Dubey, F. Rosei, and G.P. Lopinski,. Small 6, 2892 (2010).
[3] S. Cristoloveanu, and S. Williams, IEEE Elec. Dev. Lett. 13, 102 (1992).
[4] B.J. Eves, and G.P. Lopinski, Langmuir 22, 3180 (2006).