The transport mechanism in nanocrystalline silicon films at low temperature

In a wide temperature range (500-20 K), we studied the electrical transport mechanism in intrinsic and P-doped nanocrystalline silicon films. We find that the HQD model successfully explains the conductivity at high temperatures (500-200K), but fails at temperature below 200K. Single activation energy W was found in the low temperature range (100-20K), which is approximately equal to the value of kBT(W [similar to] 1-3kBT). It is in good agreement with the characteristics of hopping conduction in amorphous semiconductor, In this paper we modified the HQD model. We consider two distinct transport mechanisms, thermal-assisted tunneling and electrons hopping through the local states near the Fermi level exist simultaneously. At high temperature tunneling transport is the main process. At low temperature transport is governed by electron hopping. On this basis, a complete analytic function of the conductivity is proposed. The function successfully explains the conductivity of intrinsic and P-doped nanocrystalline silicon films in the whole temperature range.