Metallicity in SrTiO3 substrates induced by pulsed laser deposition

Abstract

Oxygen deficiency has been known to induce metallic conduction in bulk and thin film SrTiO3 (STO). Here, we report on the metallicity of STO substrates induced by the pulsed laser deposition (PLD) process of STO films under various oxygen-poor growth conditions. Depositions as short as 2 min result in conduction through the STO substrate. Films grown on other substrates are insulating, and STO substrates annealed under the same growth conditions without laser ablation remain insulating. By varying background gas composition during deposition, we find that the transport behavior transitions from metallic to insulating behavior at progressively higher ambient pressures for O2, 99% N2/1% O2, N2, and Ar. Metallic behavior persists to deposition pressures as high as 10−2 Torr in Ar. These results suggest that, during the PLD process, the deposition kinetics and plume energy are a dominant factor in the formation of oxygen vacancies which then diffuse into the substrate. Understanding these mechanisms is crucial to prevent STO substrate reduction during PLD of films which require low O2 partial pressures during growth.