Nanoscale physics

Simulation of field effect in porous silicon nanostructures 
L. Monastyrskii, I. Olenych, B. Sokolovskii
Ivan Franko National University of Lviv, 50 Dragomanov Str., Lviv-79005, Ukraine. E-mail: iolenych@gmail.com

In recent years, much attention is paid to the study of sensory properties of porous silicon (PS) nanostructures because of high surface to volume ratio [1, 2]. The sponge-like geometrical structure of the PS grants significant sensitivity of its electrical parameters to external environmental influences. A common feature of most gas sensors based on the PS is that they use adsorption-electric effects resulting in changes in conductivity and capacity of the porous layer. Besides, it was found that the large curvature of the pore surface affects the non-uniform spatial distribution of electrostatic potential in the PS with spherical topology [3]. However, a model with cylindrical pores corresponds better to the real PS structure. Therefore, the purpose of our work was to study the field effect features in the PS with a cylindrical pore shape. 
The spatial distribution of the potential was obtained by computer simulation of the nonlinear Poisson’s equation. The coordinate dependences of the electrostatic potential were analyzed for different values of the pore radius and the distance between pores. On the basis of the obtained dependences, it has been established that an increase in the surface curvature causes a decrease in the Debye screening length and a reduction in surface potential. The carrier redistribution which accompanies the field effect can not only give rise to changing the electrical conductivity of the porous layer but also to conductivity inversion. The inversion depth depends on the magnitude of the surface charge. The obtained results can be used to improve the functional characteristics of gas adsorption sensors based on the porous silicon.

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