Effect of thickness on metal-to-semiconductor transition in 2-dimensional TiN thin films

Abstract

Titanium nitride thin films have been grown on c-plane sapphire substrates using a pulsed laser deposition technique in the thickness range of 6–45 nm. X-ray diffraction (XRD) analysis has demonstrated TiN (111) as the preferred orientation of growth on the sapphire substrates. The XRD measurements have also indicated that orientational alignment between the TiN and the sapphire improved with an increase in the TiN film thickness. A change in the resistivity behavior of the TiN thin films from metallic to semiconducting has been observed as the TiN film thickness is reduced below 15 nm. Analyzing and fitting of TiN films’ conductivity data have shown that while the Arrhenius law governs their conductivity in the temperature range of 300–350 K, conductivity values of the films follow the variable range hopping mechanism below 300 K.

Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation

“…This behavior is attributed to the size effect of islands in an almost non-continuous thin-film structure. Applying the idea of the density of states and the Fermi function in region I, it can be shown that E normalg ∝ N E D 3 and normalΔ E ∝ 1 D 3 . , As shown schematically in Figure b, the separation between energy states (Δ E ) and the separation between the valence and conduction band (i.e., bandgap, E g ) increase with a reduction in the island dimension ( D ). If Δ E is more than E g , the excitation of an electron from the valence band to the conduction band is restricted and unoxidized TiN films, which should have ideally behaved metallic, start exhibiting high resistivity and semiconductor characteristics…”