  Si doped ZnO thin films with Si concentrations ranging from 0.4 to 10 % have
been grown by sequential pulsed laser deposition on sapphire substrates. The
resistivity of the films first decreased from ~ 6.6x10-3 to 4.7x10-4 ohm-cm as
the Si concentration was increased from ~ 0.4 to 2% and then it increased with
further increase in Si concentration. The electron concentrations in the films
were in the range from 3x1019 to 4x1020 cm-3 showing their degenerate nature.
However, temperature dependent resistivity measurements in the range from 300
to 4.2 K revealed negative temperature coefficient of resistivity (TCR) for the
0.4, 6 and 10% Si doped ZnO films in the entire measurement temperature range.
The 0.6, 0.9 and 2% Si doped films showed a transition from negative to
positive TCR with increasing temperature. The negative magnetoresistance found
in the films at low temperatures and 0.5 T magnetic field pointed to weak
localization as the dominant contributor towards negative TCR. A quantitative
fit of the temperature dependent resistivity data for all the films could be
obtained by considering the quantum correction to conductivity arising due to
disorder induced weak localization effect.

Materials Science