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 temperatu res (500-200K), but fails at temperature below 200K. Single activation ener gy TY was found in the low temperature range (100-20K), which is approximat ely equal to the value of k(B)T(W similar to 1-3k(B)T). It is in good agree ment with the characteristics of hopping conduction in amorphous semiconduc tor, In this paper we modified the HQD model. We consider two distinct tran sport mechanisms, thermal-assisted tunneling and electrons hopping through the local states near the Fermi level exist simultaneously. At high tempera ture tunneling transport is the main process. At low temperature transport is governed by electron hopping. On this basis, a complete analytic functio n of the conductivity is proposed. The function successfully explains the c onductivity of intrinsic and P-doped nanocrystalline silicon films in the w hole temperature range.