Quantum size effects on the conductivity in porous silicon

The quantum confinement effect was examined by measuring dark conductivity and optical transmittance of free-standing porous silicon films of different porosities. With increasing porosity from 40 to 80%, the transmission spectrum shows a blue shift and the activation energy of the conductivity increases from 0.3 to 1.0 eV. Using the activation energies, confinement energies are estimated with respect to the crystallite size, determined from the given porosity, and the results are compared with previous works. Good agreement is obtained.