Girjesh Dubey

PhD Student

Université du Québec
Institut national de la recherche scientifique
Énergie, Matériaux et Télécommunications
1650, boulevard Lionel-Boulet
Varennes, Québec, Canada
J3X 1S2

Telephone: +1 (450) 929-8246
Fax: +1 (450) 929-8102
dubey@emt.inrs.ca
www.emt.inrs.ca

Girjesh Dubey Curriculum Vitae (11/2005)

* * * * *
I am primarily interested in studying the electronic properties of organically modified semiconductor surfaces with view to exploring the potential of these surfaces for molecular sensing applications. Molecular monolayers covalently attached to silicon can be used as simple passivating layers, stabilizing the electronic properties of the surface. Attachment of organic functional groups can create active surfaces for the immobilization of chemical and biomolecular species. Charge re-arrangment at the semiconductor surface can alter the conductivity of the substrate through long-range field effects, facilitating the monitoring of adsorption and reaction events at these surfaces. The surface chemistries for monolayer formation are relatively well developed but the electronic properties have received comparatively less attention.
Experimental techniques to be employed include four point probe measurements in the Van der Pauw geometry to measure the conductivity of modified Si and silicon on insulator (SOI) substrates. Time dependent conductivity measurements are useful for monitoring changes in majority charge carrier concentration induced by band bending phenomena arising from growth of surface state charge traps or local external electric fields induced by adsorbed species. SOI substrates, where the thickness of the top silicon layer is less than or equal to the thickness of the depletion layer, are particularly sensitive to these effects. These substrates also facilitate systematic studies as the thickness of the top layer is reduced into the quantum regime. Band bending effects are also studied by surface photovoltage measurements- measuring the difference in surface potential in the dark versus under illumination (flat band condition) using a Kelvin Probe. Other surface science probes such as ellipsometry, contact angle, high resolution electron energy loss spectroscopy, X-ray photoemission and scanned probe microscopies are used to verify the structure and chemical composition of the modified surfaces.
Some key questions to be answered in our investigations include;
How well do alkyl monolayers passivate the electronic properties of the surface?
What is the sensitivity of these modified surfaces to ionic solutions, pH?
Can immobilization of biomolecular species on functionalized monolayers be monitored through surface conductivity measurements? With what sensitivity?
Can molecular modification be used to controllably alter the conductivity of silicon by functionalization with electron donating/withdrawing species?
As the thickness of the silicon substrate is reduced at what point do classical band-bending models breakdown? Can we observe the transition to quantum behavior in ultrathin SOI substrates?