Out-of-plane interface dipoles and anti-hysteresis in graphene-strontium titanate hybrid transistor

Abstract

The out-of-plane electric polarization at the surface of SrTiO 3 (STO), an archetypal perovskite oxide, may stabilize new electronic states and/or host novel device functionality. This is particularly significant in proximity to atomically thin membranes, such as graphene, although a quantitative understanding of the polarization across graphene-STO interface remains experimentally elusive. Here, we report direct observation and measurement of a large intrinsic out-of-plane polarization at the interface of singlelayer graphene and TiO 2-terminated STO (100) crystal. Using a unique temperature dependence of anti-hysteretic gate-transfer characteristics in dual-gated graphene-on-STO field-effect transistors, we estimate the polarization to be as large as ≈12 μC cm −2 , which is also supported by the density functional theory calculations and low-frequency noise measurements. The anti-hysteretic transfer characteristics is quantitatively shown to arise from an interplay of band bending at the STO surface and electrostatic potential due to interface polarization, which may be a generic feature in hybrid electronic devices from two-dimensional materials and perovskite oxides.

Resistance hysteresis correlated with synchrotron radiation surface studies in atomic sp2 layers of carbon synthesized on ferroelectric (001) lead zirconate titanate in an ultrahigh vacuum

“…19 In the rst case, this transition was explained by electrolyte insertion between graphene and the ferroelectric "compensating for anti-ferroelectric effects", while in the second it was "attributed to the dynamic response of interface screening charges that are activated by the combined effects of electric eld and temperature". It was then recognized that working in cleaner conditions is needed and a few years ago experiments were reported in vacuum in the range of 10 À3 to 10 À4 Pa. [20][21][22] Other precautions in terms of cleanness were undertaken, including thermal treatment. 1,23,24 However, the results were not concluding in all cases and it was acknowledged that even working in the above vacuum conditions, the inuence of chemisorbed OH À and H + cannot be ruled out.…”

“…1,23,24 However, the results were not concluding in all cases and it was acknowledged that even working in the above vacuum conditions, the inuence of chemisorbed OH À and H + cannot be ruled out. 22 The charge carrier density in 1 ML graphene is insufficient to screen a polarization exceeding a few tenths of C m À2 , 2,14 see also the evaluation a few paragraphs below. In addition to the above mentioned hypotheses, other extrinsic compensation mechanisms were proposed, such as charge transfer driven by electronegativity differences between outermost atoms from ferroelectrics and carbon, 25 direct interaction of graphene with defects, which modify carbon hybridization from sp 2 to sp 3 or charge injection into interfacial traps, 1 dynamic accumulation of oxygen vacancies near the interface, forming a layer with different dielectric constant, 26 charge trapping prevailing over ferroelectric effects, 6 "intrinsic bulk ferroelectric hysteresis in combination of an oxygen-decient surface layer", 20 O 2 /H 2 O redox couple intermediated by graphene charging.…”

Unveiling Temperature-Induced Structural Domains and Movement of Oxygen Vacancies in SrTiO3 with Graphene

“…Further, antihysteresis in graphene square resistance, when back gated through STO has been reported by several groups and is an active area of research. 17 , 19 , 21 …”

Temperature and Electric Field Dependence of Spin Relaxation in Graphene on SrTiO3

“…The surface of STO has a broken inversion symmetry and is found to harbor surface dipoles where the oxygen atoms are displaced outwards . The strength of these surface dipole moments is calculated to be which increases to with the graphene layer . This electric field, pointing outwards from the substrate plane, originates from the surface dipoles in STO.…”

“…Further, distinct from most other substrates on which charge and spin transport in graphene has been studied, the broken inversion symmetry at the surface of STO leads to Rashba spin orbit fields that can be tuned by an electric field . Recently it was demonstrated that electric dipoles, formed at the surface of STO, results in a large out of plane electric polarization that influences the charge transport in graphene . STO undergoes a ferroelastic transition changing from cubic ( a = 3.905 Å) to tetragonal symmetry () at T = 105 K .…”