Special features of the electrical conductivity in doped α-Si:H films with silicon nanocrystals

The electrical properties of undoped and phosphorus-doped α-Si:H films with Si nanocrystals are studied. The silicon nanocrystals are formed by a solid-solid phase transition resulting from the nanosecond effect of a XeCl excimer laser on an amorphous film. The formation of the nanocrystals in the undoped films is accompanied by an increase in the electrical conductivity by two to three orders of magnitude and a simultaneous decrease in the effective activation energy of the conductivity from 0.7 to 0.14 eV. The nanocrystal sizes range from 2 to 10 nm for various laser treatment modes and are determined from Raman scattering data and high-resolution electron microscopy. The temperature dependence of the Fermi level is obtained by calculating the energies of the localized states of electrons and holes in the nanocrystals. It is shown that, as the temperature decreases, the Fermi level tends to the energy of the states in the Si nanocrystals for a wide concentration range of the dopant. The Fermi level’s location close to the states in the nanocrystals is a consequence of the fact that these states are multicharged. It is found that phosphorus effectively transforms into an electrically active state during laser treatment of the doped amorphous Si films, which is an important consideration in the fabrication of shallow p-n junctions and contacts for amorphous Si films.