Parallel Band and Hopping Electron Transport in SrTiO₃

Abstract

SrTiO3 (STO) is a model system for studying oxide electronic devices. This work examines the electronic transport through a heterostructure comprising an acceptor (Fe)‐doped STO layer on a donor (Nb)‐doped STO substrate. This is done by fitting the steady‐state current–voltage (I–V) curve measured at ambient temperature to numerical solutions of the drift‐diffusion equations of itinerant (i.e., free) electrons and holes (band conduction) and localized electrons hopping through defect states within the bandgap (hopping conduction). The analysis shows that at reverse bias and small forward bias the current is carried mostly by hopping electrons that give rise to unexpectedly high currents. At forward bias above 1 V, most of the current is due to electron transport through the conduction band. The transition from hopping to band conduction occurs when the quasi Fermi levels of electrons and holes depart from the energy level of the defect states through which the electrons hop. These observations shed new light on the transport properties of STO‐based devices at ambient temperatures wherein ionic defects such as oxygen vacancies are immobile and holes are trapped, for the most part.

Compromising Between Phase Stability and Electrical Performance: SrVO3–SrTiO3 Solid Solutions as Solid Oxide Fuel Cell Anode Components

“…Therefore, the contribution of electron hopping between V 4+ /V 3+ couple to total electronic conductivity is likely to be limited. Instead, electronic transport is expected to occur mainly by either itinerant electrons in the conduction band formed by Ti cations, or by hopping of localized electrons between Ti 4+ /Ti 3+ couples, or by a combination of mechanisms . Reducing the oxygen partial pressure results in an increasing fraction of Ti 3+ cations (i.e., charge carriers associated with Ti cations); even if [Ti 3+ ] is still lower or comparable to [V 4+ ], this is accompanied by a smooth increase of the conductivity for compositions with y ≥0.7 (Figure ).…”

Heterogeneous Doping to Improve the Performance of Thin-Film Hematite Photoanodes for Solar Water Splitting

“…A similar p-type to n-type inversion was observed in Fe-doped SrTiO3 thin films on Nb-doped SrTiO3 (n-type) substrates, as reported elsewhere. 27 Domen et al reported a similar effect in La5Ti2CuS5O7 photoelectrodes that displayed ambipolar photocurrents depending on the current collector electrode on which they were deposited. 28 Of all the photoelectrodes in this study, the Zn-doped one (red curve) displayed the lowest onset potential, but also the lowest plateau photocurrent at high potentials (> 1.4 VRHE).…”

Thermally stimulated relaxation and behaviors of oxygen vacancies in SrTiO3 single crystals with (100), (110) and (111) orientations

“…The oxygen vacancies with relatively low formation energies can also play a critical role in determining the surface and electronic properties of SrTiO 3 . Experimental and theoretical studies have proved that the lowest energy charge state for oxygen vacancies with chemical stability is +2 in the vast majority of conditions [5,14,15]. Based on the assumption that oxygen vacancies in SrTiO 3 carry positive charges, Chiang et al proposed that oxygen vacancies provide the dominant contribution to tilting grain boundaries by the positive core charge in SrTiO 3 [13].…”

“…The correlation barrier hopping has been found to be prevailing in the conduction mechanism of crystals [10]. The analysis of Fe:STO/Nb:STO heterostructure shows that electron hopping through localized defect states such as oxygen vacancies within the band gap is dominant at reverse and low forward bias [14]. Using anelastic relaxation measurements, two main relaxation mechanisms in oxygen deficient SrTiO 3 are identified with hopping of isolated oxygen vacancies over a barrier of 0.60 eV and reorientation of pairs of vacancies involving a barrier of 0.97 eV [15].…”