Interface interaction between thin films of transition metal compounds and silicon substrates across the native SiO2 layer

FeSi films deposited on the native oxide layer on silicon substrates have been shown to undergo a metal-like to insulator-like transition around the temperature of 250 K. Near room temperature the current was carried through the silicon substrate as a result of carriers tunneling across the film–substrate interface. This was facilitated by the formation of an ohmic contact to the silicon substrate across the SiO2 layer. Rapid increase in the film–substrate interface resistance near 250 K switched the current to the film giving rise to a more than three orders of magnitude change in resistance. CoSi and Fe2O3 films deposited on silicon substrates also showed a similar transition in resistance near 250 K while resistance increased monotonically without any sign of a transition for TiSi and TiO2 films. However, TiO2 films doped with 6% Co behaved similar to films of Fe and Co compounds. These results conclude that the transition metal ions with multiple valences are important for the formation of an ohmic contact and the subsequent resistive transition. The magnitude of the transition was seen to depend on the energy of the depositing species during film growth. Ablation at high laser fluencies produced highly excited and ionized species. High density of interface states produced by energetic transition metal ions increased the hopping probability of carriers leading to a lower interface resistance. Formation of an ohmic contact between a metal electrode and the silicon substrate across the native SiO2 layer in Metal/FeSi/SiO2/Si structures has been demonstrated.