The increase of activation energy with deceasing film thickness can be understood from the island structure theory based on tunneling of charged carriers between islands separated by short distance .
The temperature co-efficient of resistance (TCR) studies of the above set of five NiO films of thickness 100, 130, 200, 250 and
300 nm, respectively were done in the temperature range of 292–382 K.
The TCR of all five films exhibits a negative value which indicates that the material NiO is a semiconducting one.