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.

Magnetism and transport in transparent high-mobility BaSnO3 films doped with La, Pr, Nd, and Gd

“…We also notice that the onset of absorption in BaSnO 3 occurs at higher energies than for SrTiO 3 , indicating that BaSnO 3 has a larger band gap than the substrate. This is consistent with the literature, where SrTiO 3 is reported to have a band gap of approximately 3.2 eV and BaSnO 3 is reported to have a band gap in the range of 3-4 eV [6,43,[69][70][71]. Since the substrate is more strongly absorbing than the film in this system and also has more features, it is useful to derive the transmittance from reflection measurements (as with ellipsometry) rather than from transmission measurements (as with uv-vis spectroscopy).…”

Oxygen diffusion in oxide thin films grown on SrTiO3

“…If there is a dynamic exchange of oxygen taking place as it will be for any ion conductor [37], this will influence locally the chemistry as well as lattice parameters of the substrate-film interface and the expected strain state for the film to grow is not automatically correct [43]. In addition, these depth profile measurements also show why additional background oxygen is needed to supplement the lost oxygen of the substrate during a heating cycle that would otherwise lead to an electrically conducting SrTiO 3−x [47,48].…”

Nature of the surface space charge layer on undoped SrTiO3(001)

“…27,49 On the other hand, the UHV annealing process, reducing condition for most of the metal oxide system, is expected to create oxygen defect states, as reported in many previous SrTiO 3 studies. 2,22,25 Until the temperature below 500 1C, no significant change in Sr 3d spectra is found across all depth ranges. However, when the temperature reaches 600 1C under UHV, a chemically stable SrO 1+x surface oxide is formed on the topmost surface as shown in Sr 3d spectra in Fig.…”

“…12,23 On the other hand, the creation of Sr vacancies (V Sr ) is also known to occur under oxygen rich PLD conditions. 2,24,25 Under the presence of oxygen species on the SrTiO 3 surface, Sr atoms make surface migration to form SrO oxide at a cost of electrons in the subsurface region, i.e., formation of an electron depletion layer near the surface. 2,24,26,27 In the case of V Sr formation, the surface resistance increases, affecting the electrical properties of the interfacial layer.…”

“…In fact, both types of V O or V Sr can occur simultaneously during the PLD process in which an oxygen environment and elevated temperature are required. 2,25 Thus, understanding the roles of these vacancies (V O and V Sr ), socalled ''defect chemistry'', has become very important to achieve reliable functionality of SrTiO 3 heterostructure systems.…”