Tunable Carrier Type and Density in Graphene/PbZr_0.2Ti_0.8O₃ Hybrid Structures through Ferroelectric Switching

Abstract

Bidirectional interdependency between graphene doping level and ferroelectric polarization is demonstrated in graphene/PbZr0.2Ti0.8O3 hybrid structures. The polarization of the PbZr0.2Ti0.8O3 can be effectively switched with graphene electrodes and can in turn alter carrier type and density in the graphene. A complete reversal of the current-voltage hysteresis direction is observed in the graphene when external environmental factors are minimized, converting p-type graphene into n-type with an estimated carrier density change as large as ~10(13) cm(-2). Nonvolatility and reversibility are also demonstrated.

Extrinsic and Intrinsic Charge Trapping at the Graphene/Ferroelectric Interface

“…Compared to what was previously reported in literature 10 , which demonstrated devices changing from anti-hysteretic to ferroelectric hysteretic behavior by increasing the gate voltage ramping rate from 0.0187 V/sec to 1.0 V/sec, the charge-trapping process associated with the observed anti-hysteresis in this case is much faster. In these devices, changing the sweeping rate of the back-gate voltage within the conventional time-scales of sub-Hz, does not appear to influence the strength of the anti-hysteresis (Figure 4b), similar to the ferroelectric-hysteresis samples (Figure 2c).…”

“…The robust nature of this antihysteresis was attributed to water molecules 8 and large densities of H + and OH -ions 9 , which screen the polarization between the graphene/PZT interface. More recently it was shown that the cleanliness of the graphene/PZT interface could be maintained by the transfer of graphene in deionized water instead of exposed to air 10 . In this work, the gating of graphene showed proper ferroelectric hysteresis, although the observation of the ferroelectric hysteresis strongly depended on ramping speed of the gate voltage.…”

Ferroelectrically driven spatial carrier density modulation in graphene

“…Graphene sheets grown via chemical vapour deposition were transferred to commercially available periodically poled and single-domain LiNbO 3 substrates (Asylum Research), using an established wet transfer process 15 . High-resolution Raman spectroscopy 21 was used to probe the graphene/LiNbO 3 structures and map the domain structure of the LiNbO 3 by measuring the shift in the frequency of the E(TO8) band that occurs near domain boundaries 22,23 (Fig.…”

“…1a, inset). On the basis of the intuitive picture described previously 15,19,20 (b) Graphene G-band frequency map. Spectra were collected simultaneously to the map in a.…”

“…Devices based on this concept have demonstrated non-volatile resistance hysteresis [13][14][15] and transparent conductivity in flexible electronics 16,17 . Initial experimental studies, however, achieved charge density changes in graphene much smaller than anticipated from full compensation of the polarization 18 , since the electrostatic coupling can be limited by extrinsic effects caused by adsorbed molecules 15,19,20 . The atomistic details and interfacial chemistry governing the interaction and the resulting charge density changes in graphene remain elusive.…”